The Climate of the Central and Northern Interior of B.C.

Clifford RaphaelDepartment of GeographyCollege of New CaledoniaPrince George, British Columbia V2N 1P8

The climate of central and northern interior BritishColumbia is examined. Although physiographicallydiverse with a variety of sub-regional and local climates,sufficient unifying influences exist to support thenotion of a regional climate. Variations in temperatureand precipitation across the region are related to lati-tude, elevation, and other local conditions. The greatestvariability in temperature occurs in winter. Variationsin temperature at Fort St. James are shown to be repre-sentative of variations at many other locations. Springis the driest season over most of the region. Extremes intemperature and precipitation are related to anticy-clonic blocking in the westerly flow. The alignment,location, intensity, and duration of the block are signifi-cant influences on the resulting temperature and pre-cipitation. Analyses of trends in temperature and pre-cipitation reveal changes that need to be assessed in thecontext of large scale causal mechanisms and in the con-text of CO2-induced climate change.

Introduction

Climate is the collective expression of weather conditions char-acteristic of a particular place in the long term. It is most oftendescribed using averages of the various weather elements.However, a complete description of the climate of a locality mustalso include the probabilities of conditions such as departures fromlong-term averages, variations, and extremes.

The purpose of this paper is to provide an overview of someaspects of the climate of the central and northern interior of BritishColumbia. There is a dearth of information on the regional climate

Western Geography, 12 (2002), pp. 230–289©Western Division, Canadian Association of Geographers

and sub-regional variations in the climate for this area. The majorfocus here will be on the mean patterns of temperature and precip-itation although consideration will be given to other climate ele-ments. Temperature and precipitation are the two key climate ele-ments influencing vegetation, soils and human activities. Toidentify sub-regional variations, spatial and temporal trends intemperature and precipitation will be considered.

For the purposes of this paper, the “region” defined as the cen-tral and northern interior of British Columbia covers an area ofapproximately 7° latitude by 7° longitude. The boundaries of theregion have been defined to correspond to the locations of existingclimate stations (Figure 1). This is a convenient definition. It can beassumed that the data recorded at a particular station are represen-tative of some surrounding district. This means that the “trueboundaries” of the region can be extended somewhat beyond theperimeter defined by the stations themselves. The region is physio-graphically diverse and contains sections of the Interior Plateau, theNorthern and Central Plateaux and Mountains, and the Great Plainsphysiographic regions of British Columbia (after Holland 1964).

The diverse nature of the region suggests that a variety of sub-regional and local climates can be expected and has been recog-nized in various climate schema for British Columbia (Chapman,1952; Kerr, 1952; Chilton, 1981; and Tuller, 1986). This varietynotwithstanding, a number of factors combine to give credence tothe notion of a regional climate. These include: the influence ofArctic airstreams on temperature and precipitation; location in thelee of the Coast Mountains and, in the case of the Great Plains sec-tion of the region, in the lee of the Rockies; influence of summerstorms because of the northward shift of cyclone tracks, and thereduced to non-existent influence of the Pacific anticyclone in sum-mer. Kerr (1952) suggested that, in spite of the variations across theregion, there is more uniformity than diversity in climate through-out the area.

Data from twelve stations located within the various physio-graphic regions are used in this discussion. These data wereobtained from the Scientific Services Division, AtmosphericEnvironment Service, Pacific Region, and the AES publications—Monthly Meteorological Summary, Canadian Climate Normals1951–1980, and Canadian Climate Normals 1961–1990. The length ofthe climate record utilized is variable. Two stations, Barkerville andFort St. James, cover 100 years of record with all other stations inthe range covering 30–60 years except Ootsa Lake with a record of22 years (Table 1, see Appendix). This discussion differs from the

The Clinate of the Central & Northern Interior of BC 231

Figure 1 Map of the study region showing station location

earlier climate studies in its specific focus on the climate of centraland northern interior British Columbia.

General Climate Controls

Climate controls refer to those large-scale factors which influ-ence the climate of a given location. For British Columbia as awhole, and for the study region in particular, several of these large-scale controls can be identified.

232 Raphael

Latitude

Latitude influences the angle of incidence of the sun’s rays(solar altitude) and day length. Together, these influence the tem-perature of a given location. The study region spans approximately7° degrees of latitude (Williams Lake 52° 11′ N, Fort Nelson 58° 50″N). Some of the variations in temperature across the region will bethe result of variations in latitude.

Latitude also influences a location’s prevailing winds. BritishColumbia’s latitude places it within the belt of the Northern hemi-sphere westerlies. The dominant airflow is west to east across theprovince. Due to the presence of the Pacific Ocean upwind of BC,maritime influences are advected onto the coast, significantly influ-encing both the thermal and moisture regimes. For central andnorthern interior British Columbia, this maritime influence,although still important, is sharply reduced because of mountainbarriers.

Mountain Barriers

The topographic profile of British Columbia is dominated byNW to SE trending mountain chains (the Western cordillera). Thestudy region is bounded by the Coast Mountains to the west andthe Rockies to the east, except for the Great Plains portion of theregion which lies to the east of the Rockies. Location in the lee ofthe Coast mountains means that stations in the region receivegreatly reduced precipitation compared to coastal stations and aremore continental in their thermal regimes. The Rockies, on theother hand, restrict the penetration of cold Arctic air into major sec-tions of the region in winter (Tuller, 1986). Cold air access is usuallylimited to the wide low passes north of 54° such as Monkman Pass,the Peace River Gap and Pine Pass (Tyner, 1957). However, in latewinter Arctic air may be deep enough to spill over the tops of themountains (Bryson and Hare 1974).

Air Masses, Fronts and Synoptic Scale Disturbances

Air masses (immense bodies of air with distinctive tempera-ture and humidity characteristics) play a crucial role in the climateof British Columbia as a whole. The temperature and humiditycharacteristics that an air mass brings to a given region are deter-mined by the characteristics of the source region and the modifica-tions that occur in transit. Fronts form the boundaries between airmasses with contrasting properties. Chapman (1952) proposed a

The Clinate of the Central & Northern Interior of BC 233

three-front model for British Columbia: the Arctic Front, separatingcontinental Arctic air from Maritime polar air, the Maritime (Arctic)Front separating Maritime Arctic air from Maritime polar air, andthe Pacific Polar front separating Maritime Polar air from MaritimeTropical air (Figure 2).

Figure 2 Three front model for British Columbia (modified afterChapman, 1952)

Air masses with either Pacific or Arctic origins vie for domi-nance in central and northern interior British Columbia. In themean for the study region, Pacific air masses dominate the circula-tion for 6–9 months (nine months in western and southern sectionssix months in north and northeast sections). Arctic air masses dom-inate for the remainder of the time. The relative dominance of theseair masses, their latitudes and their characteristics change with theseasons (Bryson and Hare, 1974). The frequency, intensity, durationand areal extent of each air mass determine the changeability of theweather for the region and also the long-term climate.

The central and western Pacific regions upwind from theBritish Columbia coast are important source areas for synoptic-

234 Raphael

scale disturbances—the familiar migratory cyclones and anticy-clones that cause large day-to-day variations in the weather (Klein,1957; Reitan, 1974; Hare and Hay, 1974). The bulk of precipitationover British Columbia is a result of the eastward movement ofthese cyclones and their accompanying frontal systems. These dis-turbances affect the region in all seasons. They are, therefore,important in determining mean patterns of temperature and pre-cipitation.

Large scale breakdowns in the normal succession of transientdisturbances determine the extremes in climate experienced acrossthe region. These breakdowns are usually associated with thedevelopment of blocking anticyclones—strong, warm-cored ridgesoccurring in the westerly flow. Anticyclones can develop in all sea-sons but especially in spring and summer. They may be centredover the Gulf of Alaska, the northern interior of British Columbia,the interior plateaux of the northwest United States, and thePacific, west of the BC coast. These blocking systems disrupt theregular west-to-east progress of migratory systems and can pro-duce anomalous weather conditions over long periods of time andlarge areas (Hare and Hay, 1974; Knox and Hay, 1984). The impactsof blocking anticyclones on temperature and precipitation patternswill be more fully developed in a subsequent section.

Semi-Permanent Pressure Centres

Three semi-permanent pressure centres influence the weatherand long term climate of British Columbia. They are the AleutianLow, the Hawaiian High (Pacific anticyclone), and the CanadianHigh (associated with the Arctic front). The influence of theHawaiian High is seen mainly in the summer in coastal and interi-or regions of southern British Columbia. It results in periods ofclear, settled weather in this part of the province but its influencerarely extends to affect the study area. Winter and spring thermaland precipitation regimes, especially over the northern parts of theregion, are significantly affected by the cold, dry conditions associ-ated with the Canadian High. Cyclonic disturbances in the wintertime over all of British Columbia, and in the summer time overnorthern British Columbia, are related to the activities of theAleutian Low.

Local Controls

Sub-regional and local variations in climate are influenced byvariations in relief across the physiographic regions included in the

The Clinate of the Central & Northern Interior of BC 235

area, elevation, local relief (valley-bottom versus valley sides),aspect (north versus south facing slopes), and urban influences.

Climate Elements

Climate elements are influenced primarily by the large scaleand local controls just outlined. A seasonal description and expla-nation of various climate elements will be the topic of this section.The standard divisions for the seasons (meteorological seasons) areas follows:

Winter: December–FebruarySpring: March–MaySummer: June–AugustFall: September–NovemberThe meteorological seasons change about three weeks ahead of

the conventional “solar” seasons. Unless otherwise noted, the“meteorological seasons” will be utilized.

Solar and Net Radiation

Temporal and spatial variations in solar radiation are keydeterminants of the variations in many other climate elements andprocesses. Variations in net radiation often mirror variations insolar radiation. The amount of solar radiation received is influ-enced by a location’s latitude and elevation, the time of year, thetime of day, and the state of the atmosphere (especially cloudcover). In addition to the factors noted for solar radiation, net radi-ation is also influenced by the albedo of the surface, air tempera-ture, and surface temperature.

Mean monthly global solar radiation values and mean month-ly net radiation values for two stations, Prince George, latitude 53°53′, and Fort Nelson, latitude 58° 50′, are depicted in Figures 3 and4. The typical patterns of solar radiation expected for middle tohigh latitude locations in the Northern Hemisphere are seen atthese two stations; radiation values are at a minimum in December(the time of the winter solstice) and at a maximum in June (the timeof the summer solstice). With the exception of April and May radi-ation values are higher at Prince George than at Fort Nelson. Thesehigher values can largely be attributed to the difference in latitudebetween the two stations.

Mean monthly net radiation values at both locations (Tuller,1986) essentially mirror the pattern of mean global solar radiationvalues. Summertime net radiation values are higher at Fort Nelson.

236 Raphael

Figure 3 Mean global solar radiation and net radiation for PrinceGeorge

Figure 4 Mean global solar radiation and net radiation for FortNelson

The Clinate of the Central & Northern Interior of BC 237

Solar Net

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

-5

0

5

10

15

20

25

Solar Net

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

-5

0

5

10

15

20

25

Negative values of net radiation occur from October throughFebruary at Fort Nelson and November through February at PrinceGeorge. These negative values probably occur as a result of a com-bination of low solar and long wave radiation inputs and high sur-face albedos as a result of snow. January albedos are estimated tobe approximately 45% at Prince George and 55% at Fort Nelson(Hay and Hare, 1974; Tuller, 1986). Temporal variations in solar andnet radiation values observed for Prince George and Fort Nelsonare believed to be representative of patterns across the region.

Temperature (Air Temperature at Screen Level)

The thermal regime of a location is controlled primarily by theavailable net radiation, air mass advection, and the storage andrelease of heat energy which are a function of surface type. Landabsorbs and releases heat energy quickly whereas water absorbsand releases heat energy slowly. As a result, air temperatures forlocations surrounded by land are more extreme than for locationsin proximity to bodies of water.

Stations in the region experience greater extremes in tempera-tures (continentality) compared to their coastal counterparts. Theseextremes result from their interior location and their location in thelee of the Coast Mountain Range which acts as a barrier to the mod-erating influence of the ocean (maritime influence). For example,the normal mean January temperatures for Prince Rupert andPrince George (at approximately the same latitude) are 0.8° C and -9.9° C respectively. The normal mean temperatures for August(Prince Rupert) and July (Prince George), the warmest months, are13.3° C and 15.3° C respectively. Temperature range for PrinceRupert is 12.5° C and for Prince George it is 25.2° C.

Annual TemperaturesTemperature data for stations in the central and northern inte-

rior B.C. are presented in Tables 2–13 (see Appendix) and Figures5–16. Data are the normals for the period 1961–1990. Mean annualtemperature generally decreases with increasing latitude and ele-vation. At Fort Nelson (most northerly location) it is -1.1° C. ForWilliams Lake (most southerly location) it is 4.1° C, and atBarkerville (highest elevation) it is 1.7° C. In addition to the latitudefactor, lower temperatures in the northern part of the region are aresult of the longer duration of Arctic air over this area. On anannual basis, Dease Lake, Fort Nelson, and Barkerville rank as thethree coldest locations. Quesnel (4.9° C) is typically the warmestlocation. This reflects a combination of lower latitude, lower eleva-

238 Raphael

tion, and other local site factors. (Note: the Williams Lake station,though further south, is approximately 400m higher than theQuesnel station.)

The timing of the occurrence of extremes in mean annual tem-peratures across the region is very consistent. For most locationsthe three coldest years on record were 1950, 1951, and 1955. Thecoldest year on record at Fort St. James was 1900 when the meanannual temperature was -1.0° C.

As will be demonstrated in a later section, temperature varia-tions at Fort St. James are highly correlated with variations at theother stations. This fact would imply that 1900 was a cold yearacross the region. The two warmest years on record at most loca-tions were 1981 and 1987. In addition, mean annual temperaturesgenerally tend to be higher in the 1980s and early 1990s.

Winter (December–February). Seasonal variations in meantemperatures generally reflect the patterns of solar and net radia-tion. Winter is the coldest season, with January typically being thecoldest month. (The lowest temperature lags the time of lowestradiation inputs). January temperatures are lowest in the northeastsector of the region (Fort Nelson -22° C) and highest in the south(Williams Lake -8.7° C) for a range of 13.3° C across the region.Similar mean January temperatures occur for stations on a west toeast line between Smithers and Prince George. Mean January tem-perature at Barkerville (-9.2° C) is comparable to that of stations atmuch lower elevations. A possible explanation is that Barkerville

The Clinate of the Central & Northern Interior of BC 239

Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec0

10

20

30

40

50

60

70

80

90

100

110

120

Precipitation (m

m)Te

mpe

ratu

re (

C)

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 5 Climograph for Williams Lake

lies above the bulk of the cold Arctic air usually occupying the val-leys at this time resulting in a milder than expected January mean.

The role of advection in influencing mean winter temperatureson time scales of days to decades cannot be underestimated.Analyses of monthly temperatures at Prince George demonstratethat the occurrence of the lowest mean monthly temperature in agiven year is determined largely by the timing, intensity and dura-tion of Arctic air incursions and not necessarily by the time of low-est radiation inputs. These cold air incursions are related to thenorthwest to southeast migration of cold anticyclones developedover the Mackenzie-Yukon-Beaufort sea region during the winter(Bryson and Hare, 1974). For Prince George, January was the cold-est month 50% of the time with November, December, andFebruary making up the other 50%. Hare and Thomas (1979) andBryson and Hare (1974) have suggested that the changing domi-nance of Arctic and Pacific air masses over the region is an impor-tant controlling influence on the winter climate. Several scenariosbased on this drama of air mass frequencies can be identified:

1. Arctic air lies over the northern parts of the region for mostof the winter (winters are cold in the north and “warm” in thesouth, e.g., winter of 1976–1977).

2. Arctic air covers the entire region reaching down intosouthern and coastal B.C. associated with outflow winds in coastalareas. Winters are bitterly cold throughout the region (e.g., wintersof 1949–50, 1968–69, and 1995–96).

240 Raphael

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

0

10

20

30

40

50

60

70

80

90

100

110

120

Precipitation (m

m)Te

mpe

ratu

re (

C)

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 6 Climograph for Quesnel

3. Several advances and retreats of Arctic air occur alternat-ing with air of Pacific origin. Winters are characterized by alternat-ing periods of relative warmth and bitter cold (e.g., winter of1981–82).

4. On other occasions Pacific air dominates a substantial por-tion of the region for most of the winter so that winter temperaturesare well above normal (winters of 1976–77, 1991–92, and 1997–98).

Extremes in temperature are also associated with this changingair mass dominance. The lowest extreme minimum temperaturesoccur in the northern part of the region (Fort Nelson - 51.7° C) buttemperatures as low as -42.2° C have been recorded at WilliamsLake, the most southerly location. The lowest extreme minimumtemperatures at the other locations lie between these two values.These minimum temperature extremes are associated with Arcticair incursions. In addition, intense radiative cooling as a conse-quence of clear skies and low humidity associated with Arctic airmasses helps to depress further the extreme minimum temperatures.

Extreme maximum temperatures in January are associatedwith air of Pacific (or southerly) origins. Lower values tend to beassociated with stations at high elevation, high latitude or both.The lowest extreme maximum value occurs at Dease Lake (8.9° C)and the highest value (15.6° C) occurs at Smithers. Walker (1961)has shown that high minimum temperatures in winter are associat-ed with southerly flow at the 700 mb level.

The Clinate of the Central & Northern Interior of BC 241

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

0

20

40

60

80

100

120

140

160

180

200

Precipitation (m

m)Te

mpe

ratu

re (

C)

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 7 Climograph for Barkerville

Summer (June–August): Summer is the warmest season withJuly being the warmest month. The occurrence of the highest meantemperatures in July illustrates the lag in air temperatures thatoccurs with respect to the time of maximum radiation inputs. Thisis typical for interior locations. Variations are apparent in meanJuly temperatures across the region. Highest mean July tempera-tures are observed at Fort Nelson (16.7° C), Quesnel (16.6° C), andFort St. John (15.8° C). Lowest mean July temperatures areobserved at Barkerville (12.2° C), Dease Lake (12.6° C), andGermansen Landing (13.8° C). Lower temperatures are affected bythe latitude and elevation of a location. Williams Lake, the mostsoutherly location, has a mean July temperature of 15.5° C. Thislower than expected value is directly related to its elevation of 940m above sea level.

High mean July temperatures at Fort Nelson are a consequenceof several factors: protection from the maritime influence by twointervening mountain ranges and longer days with greater num-bers of sunshine hours (Chapman, 1952; Chilton, 1981). The coinci-dence of highest mean July temperature and lowest mean Januarytemperature gives Fort Nelson the distinction of being the locationwith the most continental thermal regime. The temperature rangeis 38.7° C. Mean July temperatures at the other stations lie betweenthe extremes mentioned above and may incorporate other influ-ences such as the presence of local water bodies (e.g., Fort St.James).

242 Raphael

Precipitation (m

m)Te

mpe

ratu

re (

C)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 8 Climograph for Prince George

The range in mean July temperatures across the region is 4.5°C, substantially less than the 13.3° C value noted for winter. Thereduced variability is a result of the fact that summer temperaturesare predominantly radiatively driven and are therefore more con-servative in contrast to the advectively driven temperatures of win-ter.

The temporal and spatial distribution of record extrememonthly maximum temperatures is noteworthy. The extremesappear to be independent of both latitude and elevation. The high-est value, 37.7° C, occurs at Fort Nelson, Quesnel, and Fort St.James. The lowest value, 33.6° C, occurs at Fort St. John. In addi-tion, the extremes are not limited to the summer months. Recordextreme maximum temperatures occur in July at four locations, inAugust at two locations, in May at five locations, and in Septemberat one location.

The spatial pattern of extreme summer minimum temperaturesis rather chaotic. The lowest value, (-7.8° C), occurs at Barkervilleand Fort St. James. The highest value, (-1.2° C), occurs at Fort St.John. The extreme minimum temperature value (-3.3° C) at Fort Nelson is higher than the value at five moresoutherly locations in the region. Extreme summer minimum tem-peratures exhibit a bimodal temporal distribution. Stations in thewest and south of the region (Smithers, Burns Lake, Ootsa Lake,Quesnel, and Williams Lake) experience their extreme values in

The Clinate of the Central & Northern Interior of BC 243

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec0

10

20

30

40

50

60

70

80

90

100

110

120

Precipitation (m

m)Te

mpe

ratu

re (

C)

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 9 Climograph for Fort St. James

June. Stations to the north and east record their extreme values inAugust.

In addition to the role played by local site factors, (e.g., aspect,exposure, cold air drainage) several other explanations are possibleto help clarify the observed temporal and spatial distributions. Theoccurrence of extreme minimum temperatures in June may berelated to the late departure of Arctic air from the region in someyears. It is instructive to note that all of the June extremes occurwithin the first two weeks of the month. The August observationsare related to the early incursion of Arctic air into the region. Again,it is instructive to note that all of the August extremes are recordedin the last two weeks of the month. The northeast sector is mostsusceptible to these early outbreaks. According to Chapman (1952),summer frost is a hazard in the northeast sector as a result of theseearly outbreaks. The higher extreme minimum values in the FortSt. John–Fort Nelson region may result from strong summer sur-face heating which is intense enough to modify significantly thelower levels of the invading air mass thus producing the higherthan expected values observed.

Spring (March–May) and Fall (September–November): Meantemperatures in spring and fall are intermediate between the win-ter and summer values. Temperatures for April and October (mid-season months) are lowest at Dease Lake, Barkerville, and FortNelson. Lower temperatures in the north are a function of the dom-inance of Arctic air over this part of the region during these months

244 Raphael

Precipitation (m

m)Te

mpe

ratu

re (

C)

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

0

10

20

30

40

50

60

70

80

90

100

110

120

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 10 Climograph for Burns Lake

(Bryson and Hare, 1974) and high albedo surfaces (lingering snowcover or early snowfall) significantly reducing the net radiation.Quesnel is the warmest location in both seasons: 5.8° C in April and5.7° C in October. Mean April temperature across the region (3.2° C)is slightly lower than the mean October value of 3.9° C. The rangein mean April temperatures (5.4° C) and mean October tempera-tures (4.7° C) is slightly higher than the range for July but againsignificantly lower than the 13.3° C value for January. Winter(January) then emerges as the season of greatest variability in meantemperatures.

Extreme maximum temperatures in spring occur in May andrange between 31.5° C at Barkerville to 36.5° C at Quesnel.Extremes in the Fall occur in September and vary between 28.9° Cat Dease Lake to 36.1° C at Quesnel. Extreme temperature minimain spring (March) and Fall (November), and to some extent Apriland October in the north of the region, more closely resemble theextremes of the winter months lending credence to the suggestionof a natural winter season for the region extending from Novemberthrough March. Minima in the spring (March) range from a low of-42.8° C at Dease Lake to a high of -31.7° C at Williams Lake with amean value across the region of -37.7° C. Minima in the Fall(November) range from a low of -42.5° C at Dease Lake to a high of-32.4° C at Smithers with a mean value across the region of -39.1° C.Lower minima in both seasons tend to occur in the north of the

The Clinate of the Central & Northern Interior of BC 245

Precipitation (m

m)Te

mpe

ratu

re (

C)

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

0

10

20

30

40

50

60

70

80

90

100

110

120

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 11 Climograph for Ootsa lake

region and at higher elevations. The role of Arctic air in influencingthe observed distribution has already been alluded to.

Precipitation

Precipitation requires the presence of water vapour in the aircolumn and condensation mechanisms to produce raindrops orsnowflakes large enough to fall to the surface. Several factors influ-ence the availability of water vapour in the air column and the inci-dence of precipitation at the surface over British Columbia as awhole and the central and northern interior region in particular.The vapour flux over the area (derived mainly from the PacificOcean) results from zonal inflow which is stronger in the winterbecause the westerly flow is stronger at this time of the year.Precipitable water—the amount of moisture in the air columnavailable to fall as precipitation—decreases in a west to east direc-tion and is lower in January than in July (Hare and Hay, 1974). Thismeans that more moisture is available over coastal locations thanover interior locations and more moisture is available in July thanin January. However, the key to the incidence and distribution ofprecipitation over British Columbia and its subregion is not theavailability of water vapour or the flux of that vapour but ratherthe operation of uplift from the scale of the local thunderstorm tothe frontal/cyclonic complex.

Over a region dominated by mountains such as is the case forBritish Columbia, orographic uplift functions mainly to enhance

246 Raphael

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

0

10

20

30

40

50

60

70

80

90

100

110

120

130

Precipitation (m

m)Te

mpe

ratu

re (

C)

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 12 Climograph for Smithers

frontal/cyclonic precipitation or enhance local convective uplift inconstricted terrain (Hare and Hay, 1974). Augmentation of precipi-tation occurs on the windward slopes with substantial reduction onthe lee side of the mountain range. The rain shadow effect increas-es with distance downwind of the mountain range. This drasticreduction in precipitation is seen in the contrast amongst meanannual precipitation totals for four locations: Prince George (609.8mm) and Prince Rupert (2414.5 mm); Williams Lake (401.6 mm)and Bella Coola (1530.2 mm). Values at the interior locales are 25%and 26% of their coastal counterparts. Although most locations inthe Central and Northern Interior show this reduction, appreciablevariations in the temporal and spatial distribution in precipitationexist for the region. In addition to variations produced by the oper-ation of different precipitation mechanisms, the overall pattern ofprecipitation across the region is conditioned further by local sitefactors such as elevation, aspect and exposure. The data portrayedin Figures 5–16 and contained in Tables 2–13 (see Appendix) cap-ture these variations.

Annual PrecipitationMean annual precipitation ranges from a high of 1042 mm at

Barkerville to a low of 416.6 mm at Ootsa Lake. Dease Lake (421.6mm) and Williams Lake (426 mm) also have low annual totals. Atmost of the other stations mean annual precipitation is less than520 mm with the exception of Quesnel (538.5 mm) and Prince

The Clinate of the Central & Northern Interior of BC 247

Precipitation (m

m)Te

mpe

ratu

re (

C)

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-50

-40

-30

-20

-10

0

10

20

30

0

10

20

30

40

50

60

70

80

90

100

110

120

130

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 13 Climograph for Germansen Landing

George (614.7 mm). Across the region, rainfall is from 50%–70% ofthe annual precipitation, being generally less important as latitudeand elevation increase. Barkerville’s high annual precipitation isrelated to its location in the Quesnel Highland (CaribooMountains), at 1265 m a.s.l., and illustrates the impact of orograph-ic lifting on precipitation enhancement. The effects of convergenceand uplift occurring in the airstream as it encounters topographicbarriers such as the Quesnel Highland can also be seen in theincreased precipitation at Quesnel and Prince George (Chilton,1981). The low annual total at Dease Lake reflect a combination ofdry Arctic air in the winter and spring months, isolation withrespect to the southerly flow of moist air in the winter (Tuller,1986), and reduced summer convective activity as a result of higherelevation (cooler temperatures).

Barkerville (1860.7 mm, 1948) and Prince George (843.7 mm,1967) record the highest maximum annual precipitation. WilliamsLake (232.9 mm, 1970) and Fort St. John (251.3, 1945) record thelowest minimum annual precipitation (Table 14, see Appendix).Although the timing of the occurrence of extremes varies across theregion, two patterns emerge when the annual data for all locationsare examined: 1) the general tendency for record wet years to bewet across most of the region (e.g. 1959 and 1962) and for recorddry years to be dry across most of the region (e.g. 1943 and 1970); 2)opposite patterns in northern and southern sections; that is, wet inthe south dry in the north, or the reverse.

248 Raphael

Precipitation (m

m)Te

mpe

ratu

re (

C)

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

0

10

20

30

40

50

60

70

80

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 14 Climograph for Dease Lake

The seasonal cycle of precipitation in the central and northerninterior region shows a distinct minimum in spring at all stationsexcept Fort Nelson where winter is the season of minimum precip-itation. This dry period actually extends from February throughMay with April being the driest month at most locations (Figures5–16). Precipitation distribution across the rest of the year is morespatially variable.

A distinct summer maximum is apparent at stations in thesouthern and northern parts of the region. At Williams Lake andQuesnel, total summer precipitation is 33.5% and 32% of the totalannual precipitation respectively. For Dease Lake, Fort St. John andFort Nelson, values range between 37.1% and 47.1% of the annualtotals. A weak summer maximum exists at three other locations:Fort St. James, Prince George, and Germansen Landing. For loca-tions with a summer maximum in precipitation, June and July areusually the two wettest months. At the four remaining locations,maximum precipitation occurs in the fall (as at Smithers 32.8% ofthe annual total) or precipitation is fairly evenly distributed acrossthe summer-fall-winter period. This even distribution is best exem-plified by the seasonal precipitation percentages for Barkerville:summer (26.3%); fall (25.7%) and winter (27.9%). Except for per-haps the two stations in the northeast, the preceding observationssupport the conclusion that precipitation falling in the colder sea-sons determines the annual precipitation pattern across the region(Walker, 1961).

The Clinate of the Central & Northern Interior of BC 249

Precipitation (m

m)Te

mpe

ratu

re (

C)

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

0

10

20

30

40

50

60

70

80

90

100

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 15 Climograph for Fort St. John

Winter (December–February): Precipitation in the winter ispredominantly in the form of snow with December and Januarybeing equally represented as the snowiest month. However, rain-fall in some winters can be a significant fraction of the overall win-ter total. For example, at Quesnel on December 10, 1980, 22 mm ofrain was recorded. This represents 17.1% of the normal total winterprecipitation. The importance of rainfall to total precipitationamounts (both absolute and relative) increases with decreasing lat-itude and altitude. At the three northern stations rainfall is lessthan 1 % of the normal winter total. At Barkerville, rainfall is 6.5%and, at Quesnel, 16% of total winter precipitation.

Air temperature and ground surface conditions (cold or snow-covered or both) in winter, render convective air motions essential-ly impossible. The absence of convective activity is replaced by anincrease in frontal/cyclonic activity. Winter precipitation is almostexclusively frontal/cyclonic in origin (Walker, 1961). Winter is theseason of the strongest westerly flow and the season of maximumintensity and frequency for cyclogenesis off the coast of BritishColumbia. Although the main storm tracks are centred far to thesouth at around 45° N, the central and northern interior region stillexperiences significant frontal activity (Bryson and Hare, 1974).The percentage of precipitation falling at Prince George whenfronts are present is: January, 100%; April, 75%; July, 41%; andOctober, 95% (Walker, 1961).

250 Raphael

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec-45

-35

-25

-15

-5

5

15

25

0

10

20

30

40

50

60

70

80

90

100

110

Precipitation (m

m)Te

mpe

ratu

re (

C)

Mean monthly precip.Mean max. temp. Mean min. temp.

Figure 16 Climograph for Fort Nelson

Mean winter precipitation values are highest at Barkerville(290.2 mm), Prince George (143.2 mm), and Smithers (135.1 mm).The lowest mean winter precipitation occurs at Fort Nelson (56.7mm), Fort St. John (83.7 mm), and Dease Lake (85.5 mm). The sup-pression of winter precipitation in the north and northeastern sec-tions of the region is of note. As mentioned earlier, this is primarilya result of the presence of cold, dry, stable Arctic air over theseareas. In years (for example, winters of 1968–69 and 1949–50) whenthe Arctic air extends to cover most if not all of the region, low val-ues of precipitation are also recorded at other locations for theduration of the outbreak event. Heavy precipitation can resultwhen a change in circulation causes the Arctic air to be replaced bya southerly flow of Pacific origin. The type and amount of precipi-tation depend on factors such as the stability, temperature andmoisture content of the new air mass, elevation and exposure of thelocation, and the temperature of the cold air trapped at the surface.

Extreme maxima and minima in winter season precipitationacross the region are presented in Table 14 (see Appendix). The dri-est winter on record (22.9 mm) occurred at Dease Lake in 1968–69.With the exclusion of Barkerville, the wettest winter on record(313.2 mm) occurred at Smithers in 1946–47. Anomalously wet ordry winters tend to occur on a region-wide basis. For example, thewinter of 1981–82 was one of record precipitation at both Fort St.James and Prince George with very wet/snowy conditions every-where else. The winter of 1986–87 was one of record dry conditionsat Quesnel, with dry conditions occurring throughout the region.

Spring (March–May): Spring is the season of transitionbetween the cyclonic storms regime of winter and the instability ofsummer. Dry Arctic air still dominates most of the region north of53° N while at the same time there is a decrease in the strength ofthe westerlies. Frontal/cyclonic activity still plays an important butdiminished role in the precipitation occurring across the region(Walker, 1961; Bryson and Hare, 1974; Tuller, 1986). Precipitation inthe spring is a mixture of snow and rain. Rainfall makes up thegreater percentage (up to 79.8% at Quesnel) of spring precipitationat all stations except Barkerville (38.6%), Dease Lake (43.1%) andFort St. John (49.2%).

The dryness of spring has already been noted. Ootsa Lake andDease Lake are by far the driest locations with a mean total springprecipitation of 60.5 mm and 63.5 mm respectively. Barkerville isthe wettest location with a mean spring precipitation of 209.1 mm.Fort Nelson (85.1 mm) and Fort St. John (85.8 mm) are both wetterin the spring than stations in the western and southern parts of the

The Clinate of the Central & Northern Interior of BC 251

region (e.g., Smithers and Williams Lake). The unexpectedly higherspring precipitation at these two northeast locations is influencedby the dramatic increase in precipitation in the month of May espe-cially evident at Fort Nelson (Figure 16). This sharp increase in pre-cipitation in May could be the result of decreased influence ofArctic air combined with an increase in convective activity relatedto increased solar radiation inputs.

Spring precipitation extrema are given in Table 14 (seeAppendix). The lowest spring precipitation value among the sta-tions (16.8 mm) was recorded at Dease Lake in 1945. Dease Lakealso has the distinction of being the location with the lowestextreme maximum spring precipitation total (114.4 mm in 1981).These data indicate that Dease Lake, in addition to being one of thecoldest locations, is also one of the driest locations in the region.Barkerville (449 mm, 1948) and Fort Nelson (182.7 mm, 1988) arethe locations with the highest record maximum spring precipita-tion.

The spring precipitation distribution is more spatially variablethan the winter pattern—more sub-regional variations are appar-ent (Table 14, see Appendix). For example, dry springs occur in thewest and northwest with wet conditions elsewhere, or wet springsoccur in the northeast and west with dry conditions in other partsof the region. The influence of local conditions may help to explainsome of this variation. Exceptions to the above would be theregion-wide very wet springs of 1981 and 1988 and the very drysprings of 1956 and 1991.

Summer (June–August): Summer is the season of maximumprecipitation at many stations across the region. Precipitation ismainly in the form of rain although most stations have recordedsmall amounts of snow in at least one of the summer months. Meanvalues for total summer precipitation range between 119.7 mm and274.3 mm. Ootsa Lake and Smithers are the two driest locationswith Barkerville being the wettest. (Barkerville’s elevation andlocation make it the wettest station in the region in all seasons.)High values of mean summer precipitation are recorded for theFort Nelson–Fort St. John area.

A number of factors combine to explain the incidence of pre-cipitation across the region in the summer. Increased solar radia-tion input coupled with late spring surges of cool, unstable air giverise to strong convective activity leading to increases in precipita-tion in June (Schaefer, 1978). Impacts of convective activity on sum-mer precipitation are best exemplified by the precipitation patternsat Fort Nelson and Fort St. John. The strong summer maximum in

252 Raphael

precipitation is typical of the convectional precipitation regime oftrue continental climates. Results from Tuller (1986) indicated thatthe Peace River region has the highest values for high intensity con-vectional rainfall—15-minute rainfall totals with a 10-year returnperiod—for all of British Columbia.

In addition to strengthened convective activity, a series of coldlows—pools of cold air aloft which become “cut off” from theupper-level westerly flow—with their inherent instability normallycross the province in late spring and early summer giving rise tofrequent showers and thundershowers (Schaefer, 1978; Oke andHay 1994). Analyses of summer data for the period 1947–1955showed that Cold Lows tracked through the study region about39% of the time (Hage, 1947 in Walker, 1961). Some estimates sug-gest that precipitation associated with Cold Lows might reach 51mm in the summer season, a large percentage of total summer pre-cipitation for many locations in the central and northern interiorregion (Walker, 1961).

A third factor influencing summer precipitation is the majorchanges that occur in the atmospheric circulation. The HawaiianHigh (Pacific anticyclone) extends northward in the upper tropo-sphere and at lower elevations usually around mid-June, althoughthe timing may vary from year to year (Bryson and Hare, 1974). Asthe Hawaiian High develops the Cold Lows are displaced(Schaefer, 1978). There is also a concomitant northward shift in themain storm tracks which are now centred around 54° N. Adecreased latitudinal temperature gradient means that the westerlyflow is weak. Although Pacific cyclones are less frequent and lessvigorous than in winter as a result, they still track through theregion and play an important role in summer precipitation (Brysonand Hare, 1974; Hare and Hay, 1974; Walker, 1961).

Extreme maximum summer precipitation values range from620.3 mm at Barkerville to 203.7 mm at Ootsa Lake. Fort Nelson(450.8 mm), Fort St. John (361.5 mm), and Dease Lake (339.2 mm)also record high maximum values (Table 14, see Appendix). Recordlow summer precipitation values range from 33.1 mm at Fort St.James to 98.1 mm at Barkerville. Williams Lake (33.3 mm) andOotsa Lake (47.2 mm) are the locations with the next lowest recordminimum summer precipitation.

Although the timing of minima and maxima varies from onelocation to the next, extreme minimum precipitation at one locationtends to occur in the context of regional dryness (e.g., summers of1967 and 1992). Record wet summers tend to follow a similar pat-tern (e.g., the summers of 1957, 1962, and 1993). Very wet summers

The Clinate of the Central & Northern Interior of BC 253

may result from a combination of enhanced frontal activity,enhanced cold low activity and enhanced convective activity.

Fall (September–October): Fall, like spring, is a transitionalseason between the regimes of summer and winter. Severalchanges important to fall precipitation patterns occur in the circula-tion in early to mid fall. The Aleutian Low, which had weakenedand been displaced north and west as the Hawaiian High shiftednorth, reappears dramatically in August (Walker, 1961) as if to sig-nal the end of summer. The westerlies strengthen, expand anddevelop a very zonal (west to east) flow pattern. The main stormtracks shift to be centred on 48° N (Bryson and Hare, 1974). Anincrease occurs in the frequency and intensity of travelling cyclonesand anticyclones and the Arctic regime establishes itself over thenorthern sections of the region by late November (Hare and Hay,1974). The sum of these changes determines the nature and magni-tude of fall precipitation.

Fall precipitation across the region is a mix of snow and rainwith rainfall greater than 55% at all locations except Fort Nelson(49.7%), and up to 77% at Smithers. Snow begins to dominate themix late in the season. For example, the normal snowfall forNovember at Prince George is 68.5% of the total precipitation. Themain causal mechanisms for precipitation in early fall arefrontal/cyclonic systems and late season convective activity. ByOctober, frontal/cyclonic systems dominate. (Walker, 1961). Theincreased frequency and intensity of these frontal/cyclonic systemsis shown by the continued high precipitation amounts in the fall(compared to summer) at locations such as Prince George and bythe increased totals over summer at locations such as Smithers(Figures 8 and 12).

Mean total precipitation value is, again, highest at Barkerville(268.3 mm). Across the rest of the area, high values occur at PrinceGeorge (171.4 mm) and Smithers (170.5 mm). Lowest mean totalprecipitation values occur at Fort Nelson (95.4 mm), Fort St. John(99.8 mm), and Williams Lake (101.4 mm). Reduction in solarinputs suppressing convective activity, increasing isolation fromthe southerly flow of moist air and the onset of the cold, dry, stableArctic regime produce a marked decrease in fall precipitation forthe Fort Nelson–Fort St. John region (northeast sector). TheWilliams Lake value probably results from a decrease in convectiveactivity and less impact of the increased frontal/cyclonic activitythat characterizes the fall.

Not surprisingly, extreme minimum Fall precipitation totals(Table14, see Appendix) are lowest in the northeast. Fort St. John,

254 Raphael

27.4 mm; Fort Nelson, 34.8 mm. Williams Lake in the south has arecord minimum of 37 mm. Barkerville (455 mm) and Smithers(287.9 mm) have the highest extreme maximum values. Althoughthere are sub-regional variations in some years, extreme dry-ness/wetness at any location tends to occur in the context ofregional dryness/wetness. For example, the fall of 1943 was thedriest fall on record at four widely spaced location: Fort Nelson,Fort St. John, Prince George, and Smithers. The fall of 1986 was thewettest fall on record at both Dease Lake and Germansen Landingwith above normal precipitation everywhere else across the region.

Anomalies in Temperature and Precipitation

The extremes in temperature and precipitation for all seasonsdescribed in earlier sections represent substantial departures fromthe long-term mean values at any location within the study area.These anomalies can usually be related to the development ofblocking anticyclones in the westerly circulation. The associationbetween blocking and unusual weather has been well documented(Andrews, 1955; Baudat and Wright, 1969; Namias, 1969; Knox andHay, 1984). Blocking anticyclones are associated with positiveanomalies in the mean pressure field at the surface and variousother levels in the atmosphere. The strength, duration, location,and alignment of the blocking ridge are all important componentsaffecting the resulting weather. Several examples of blocking anti-cyclones and their impacts on extremes in weather for the studyregion are presented in this section.

Figures 17–23 are maps of the 500 mb level, showing the meanpressure field and anomalies for the periods indicated. Four peri-ods from the winters of 1968–69 and 1997–98 are depicted onFigures 17–20. Of note for the winter of 1968–69 (Figures 17 and 18)is the strong ridge positioned off the coast of British Columbiaaligned southeast to northwest and the deep trough over westernCanada. This alignment interrupts the normal west-to-east pro-gression of migratory systems and allows cold Arctic air to bepulled down in the trough behind the ridge covering all of thestudy region. Record low temperatures and below normal precipi-tation were reported for a number oflocations throughout BritishColumbia, including five locations in the study region, duringthese two events (Baudat and Wright, 1969). In contrast, for thewinter of 1997–98, ridging at the 500 mb level was less intense withthe blocking ridge centered on two different locations. In earlyJanuary 1998 (Figure 19), the ridge was centred off the coast of

The Clinate of the Central & Northern Interior of BC 255

256 Raphael

Figure 17 Map of the 500 mb level showing the mean pressure fieldand anomalies for December 25–31, 1968

Figure 18 Map of the 500 mb level showing the mean pressure fieldand anomalies for January 23–30, 1969

The Clinate of the Central & Northern Interior of BC 257

Figure 19 Map of the 500 mb level showing the mean pressure fieldand anomalies for January 8–11, 1998

Figure 20 Map of the 500 mb level showing the mean pressure fieldand anomalies for January 25–31, 1998

258 Raphael

Figure 21 Map of the 500 mb level showing the mean pressure fieldand anomalies for May 27–31, 1983

Figure 22 Map of the 500 mb level showing the mean pressure fieldand anomalies for September 1–5, 1988

Figure 23 Map of the 500 mb level showing the mean pressure fieldand anomalies for July 9–12, 1990

British Columbia allowing, cold air to invade the trough over west-ern Canada; temperatures were below normal but substantiallywarmer than in 1968–69. In the latter part of January 1998 (Figure20), the ridge was centred over western Canada. The southwest-to-northeast alignment of the isobars favoured advection of warm airfrom the southwest at middle and upper levels. Temperatures weresubstantially above normal during the period.

Examples of anticyclonic blocking in spring, summer and fallare shown on Figures 21–23. Although there are some differences inthe intensity, location, and alignment of the blocking ridge, in eachinstance, the ridge configuration facilitates the flow of warmer airinto the region. In May 1983 and September 1988, record or abovenormal temperatures were observed at all locations in the studyregion.

Anomalously dry conditions can generally be linked to block-ing systems. Anomalously wet conditions can conceivably occur inconjunction with blocking (the location of the anticyclonic centrewould be important) but may result from a variety of different fac-tors. For example, due to the strong zonality in the westerly flow inthe fall, extreme or above normal fall wetness across the region

The Clinate of the Central & Northern Interior of BC 259

may be related to more frequent and intense frontal/cyclonic sys-tems crossing the region.

Climate Trends, Variability and Change

Variability

Several aspects of the temporal and spatial variability in tem-perature and precipitation across the region have already been dis-cussed. Some further comments on variability will be the topic ofthis section.

The difference in mean temperature from year to year (theinterannual variation), can be used as a measure of temporal andspatial variability in the temperature field. Time series of interan-nual variations in seasonal and annual temperatures were derivedfor several locations: Prince George, Smithers, Quesnel, WilliamsLake, Fort Nelson, Dease Lake, and Fort St. James. Interannualvariations at the other locations were compared to the Fort St.James data (Fort St. James is the location with the longest, most reli-able, complete record for temperature and precipitation in theregion). Results for two locations, Prince George and Fort Nelson,for the winter season are shown on Figures 24 and 25. It is quiteclear from the data presented that a high degree of correspondenceexists between interannual variations at Fort St. James and thesetwo locations in winter.

The correlation between interannual variations at Fort St.James and the six other locations was assessed for seasonal andannual values. Figure 26 shows the correlation coefficients plottedagainst straight line distance of the station from Fort St. James.Even though mean winter temperatures show the greatest rangeacross the region, interannual variations in seasonal temperaturesacross the region tend to be most conservative in winter and mostvariable in spring. Correlation coefficients in all seasons are statisti-cally significant: highest at Prince George and lowest at FortNelson. Some directionality is apparent; that is, Smithers to thewest, has lower correlations than Quesnel, to the south, eventhough it is closer to Fort St. James. This may be related to the factthat stations are in different physiographic regions. Results alsoindicate that data at Fort St. James can be used to represent temper-ature variations over large sections of the study region and wouldtherefore be useful for additional analyses of the climate of theregion. The spatial patterns are indicative of similar forcing factors

260 Raphael

for temperature across the area and further support the regionaldesignation assumed herein. The consistently lower correlationsfor Fort Nelson suggest that this location should be treated sepa-rately.

Variations in precipitation were assessed using the coefficientof variation (standard deviation/mean), a relative measure of thedispersion in a data set (see Table 14, Appendix). In all seasons andat all locations, the year to year variation in precipitation is high.Greatest variability at a given locale and across the region tends tooccur in the summer. This is a reflection in part of the role of local-scale convectional precipitation in influencing summer totals. Theleast variability exists for annual precipitation totals. The greatestvariability in precipitation across the seasons occurs for WilliamsLake and Fort St. John. The least variability occurs for Burns Lakeand Prince George.

Figure 24 Comparison of interannual variations in winter tempera-tures for Fort St. James and Prince George

The Clinate of the Central & Northern Interior of BC 261

Tem

pera

ture

Var

iatio

ns (

C)

Fort St. James Prince George

1944 1950 1960 1970 1980 1990

-10

-8

-6

-4

-2

0

2

4

6

8

10

Figure 25 Comparison of interannual variations in winter tempera-tures for Fort St. James and Fort Nelson

Figure 26 Interannual temperature correlation: Variation with dis-tance

262 Raphael

Tem

pera

ture

Var

iatio

ns (

C)

Fort St. James Fort Nelson

1944 1950 1960 1970 1980 1990

-10

-8

-6

-4

-2

0

2

4

6

8

10

Co

rre

latio

n C

oe

ffic

ien

t (%

)

121(Prince George)

194(Smithers)

206(Quesnel)

303(Williams Lake)

509(Fort Nelson)

582(Dease Lake)

60

65

70

75

80

85

90

95

100

Distance (km) from Fort St. James

Climate Trends and Change

The concern over climate change as a result of CO2-inducedgreenhouse warming is an issue for this region. Climate change,typically indicated by changes in temperature, would affect severalspheres of human activity (e.g., energy utilization and forestrypractices) (Raphael, 1993). Change, if any, must be assessed in thecontext of the historical climate record for a region. Ideally, trendsin the existing record must be identified, analyzed and explainedbefore anything definitive can be said about CO2-induced warm-ing. A recent study, (Raphael, 1993), assessed the temperaturetrends at Prince George for the period 1943–1991. Results indicatedsignificant increases in winter, spring, summer and annual meantemperatures at this location over the 49-year period. Changes inwinter and spring were the most important. Temperature trendswere similar to Canadian, northern hemisphere, and global trendsfor the same period (Berry,1991). Similar trends were also observedat other locations in the region (e.g., Smithers).

In addition to the Raphael (1993) study, trends in temperaturefor the region were assessed using data at Fort St. James. Decadalmeans were derived for annual and seasonal mean minimum andmean maximum temperatures. Ten decades are represented in thedata. Decades were chosen to coincide with the 10-year periods ofthe Canadian Climate Normals. For example, the period 1971through 1980 constitutes the decade of the 1970s. The period1895–1900 is used to represent the decade of the 1890s. The devia-tions of the decadal means from the 1961–1990 climate normalswere calculated and are depicted on Figures 27 and 28. Thesegraphs indicate that: 1) all decades are colder than the 1961–1990normals except the 1980s; 2) there is a warming trend in mean min-imum temperature with the 1980s being the warmest decade, and 3) the most recent climate normals represent a warmer (at leastwith respect to mean minimum temperatures) sequence in the cli-mate of the region. Results for mean maximum temperatures (notshown) are more variable but also show the 1980s as one of thewarmest decades.

Cumulative deviations from the long-term mean were also cal-culated for annual and seasonal mean minimum temperatures. Thecumulative deviation is the difference between the elementvalue(in this case mean minimum temperature) for a particularyear and the long-term mean for the data set, plus the sum of thedeviations from all preceding years. Decreasing values of thecumulative deviations are associated with years in which element

The Clinate of the Central & Northern Interior of BC 263

Figure 27 Fort St. James: Mean minimum temperature (annual values); deviation from the 1961–1990 normal

Figure 28 Fort St. James: Mean minimum temperature (seasonal values); deviation from the 1961–1990 normal

values are below the long-term mean. Increasing values are associ-ated with years in which element values are above the long-termmean. Cumulative deviations can be used to identify the timing

264 Raphael

Dev

iatio

n (C

)

1890s 1910s 1930s 1950s 1970s-5

-4

-3

-2

-1

0

1

Decade

Dev

iatio

n (C

)

1890s 1910s 1930s 1950s 1970s

Decade

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

Winter Spring Summer Fall

and nature of climate variations at a particular location (Linacre,1992 and Raphael, 1993). Figure 29 shows cumulative deviationsfor annual and winter mean minimum temperatures. The annualvalues fall into three distinct periods: a period of below averagemean minimum temperatures from 1895–1922; a transitional peri-od (with values close to the long-term mean) from 1922–1950; and aperiod of above average mean minimum temperatures from1951–1990. Winter values are much more variable. The period ofbelow average values from 1895–1922 is largely present; subse-quent to this, several periods alternating between above/belowaverage temperatures are evident.

Analyses of long term precipitation data for Fort St. Jamesusing cumulative deviations (Figures 30 and 31) reveal importanttrends in annual and seasonal precipitation: the period prior to themid-1940s being characterized by below average precipitation andthe period until about the early 1980s characterized by above aver-age precipitation. Large scale causal mechanisms (e.g., El Nino, air-mass frequency changes) are implicated in these temperature andprecipitation trends. The role of these mechanisms needs to beresolved definitively before any understanding of the impacts ofCO2-induced climate change on the region can be fully realized.

Figure 29 Fort St. James: Mean minimum temperature; deviationfrom the 1895–1990 mean

The Clinate of the Central & Northern Interior of BC 265

Cum

ulat

ive

Dev

iatio

n (C

)

Annual

1895 1900 1920 1940 1960 1980-60

-50

-40

-30

-20

-10

0

10

Year

Winter

Figure 30 Fort St. James annual precipitation: deviation from the1900–1990 mean

Figure 31 Fort St. James winter precipitation: deviation from the1900–1991 mean

266 Raphael

Cum

ulat

ive

Dev

iatio

n (m

m)

Year

1900 1920 1940 1960 1980

-2500

-2000

-1500

-1000

-500

0

500

Cum

ulat

ive

Dev

iatio

n (m

m)

1900

Year

1920 1940 1960 1980

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

100

Conclusion

The aim of this paper has been to provide an overview of someaspects of the climate of the central and northern interior of BritishColumbia. Local scale variations dictate that there be several sub-regional variants in climate over such a large area. However, theperspective adopted in this paper is that there are enough unifyingfactors (e.g., the role of Arctic airmasses) to view the climate of thisregion as a single entity, distinct from coastal climates or climates ofthe southern interior of British Columbia.

The climate of the central and northern interior of BritishColumbia region is, in essence, a climate of austerity. It is character-ized by long, cold and sometimes very severe winters especially inthe northern sections and cool to warm (occasionally hot), and inmost instances, wet summers. Every season can be given toextremes in temperature and precipitation. The inhabitants of thisregion must be commended for their adaptability and resilience inthe face of a harsh and sometimes unforgiving climate.

Acknowledgements

Data for this study were courtesy of Environment Canada. I amgrateful to the many College of New Caledonia students whoassisted as work-study students at various stages of this project.The efforts of Jason Gilkes, Jennifer Hay, D’arcy Henderson, andCarell James are especially noteworthy. Brendan Murphy’s assis-tance in producing a number of the figures is worthy of note. I amalso grateful to Drs. Michael Church, Marilyn Raphael, and StanTuller who reviewed the manuscript and provided many helpfulcomments. Finally, I give thanks to God for his enabling grace.

References

Andrews, J. F. (1955). The Weather and Circulation ofDecember 1955. Monthly Weather Review, 83 (12), 327–335.

Baudat, C. and Wright, J.B. (1969). The Unusual Winter1968–1969 in British Columbia. Canada. Department of Transport,Meteorological Branch, Technical Memoranda 730.

Berry, M.O. (1991). Recent temperature trends in Canada. TheOperational Geographer, 9(1), 9–13.

Bryson, R.A. and Hare, F.K. (Eds) (1974). Climates of NorthAmerica. Amsterdam-London–New York: Elsevier ScientificPublishing Company.

The Clinate of the Central & Northern Interior of BC 267

Canada (1982). Canadian Climate Normals, Volume I, SolarRadiation, 1951–1980. Ottawa: Environment Canada, Atmospheric EnvironmentService.

Canada, (1993) Canadian Climate Normals, British Columbia,Volume I 1961-1990. Toronto: Environment Canada, AtmosphericEnvironment Service.

Chapman, J.D. (1952). The Climate of British Columbia. Paperpresented to the Fifth British Columbia Natural ResourcesConference. 47 pp.

Chilton, R.R. H. (1981). A Summary of Climatic Regimes of BritishColumbia. Victoria: British Columbia, Ministry of Environment,Assessment and Planning Division.

Hage, K.D. (1957). On Summer Cyclogenesis in Western Canadaassociated with Upper Cold Lows. University of Chicago, Departmentof Meteorology, Scientific Report No. I, Contract AF 19(604) 2179.

Hare, F.D.K. and Hay, J.E. (1974). The Climates of Canada andAlaska. In R.A. Bryson and F.K. Hare (Eds.), Climates of NorthAmerica. Amsterdam-London-New York: Elsevier ScientificPublishing Company.

________, and Thomas, M.K. (1979). Climate Canada. Toronto:Wiley Publishers of Canada Limited.

Holland, S.S. (1964). Landforms of British Columbia: APhysiographic Outline. Victoria: British Columbia, Department ofMines and Petroleum Resources, Bulletin No. 48.

Kerr, D. (1952). The Climate of British Columbia. CanadianGeographical Journal, 45, 143–158.

Knox, J.L. and Hay, J.E. (1984). Blocking Signatures in theNorthern Hemisphere: Rationale and Identification. Atmosphere-Ocean, 22(1), 36–47.

Linacre, E. (1992). Climate Data and Resources: A reference andguide. London and New York: Routledge.

Namias, J. (1969). Seasonal Interactions between the NorthPacific Ocean and the Atmosphere during the 1960’s. MonthlyWeather Review, 97(3), 173–192.

Oke, T. And Hay, J. (1994). The Climate of Vancouver. 2nd Edition.Vancouver: B.C. Geographical Series, Number 50, Department ofGeography University of British Columbia.

Raphael, C. (1993). Temperature Trends at Prince George,British Columbia (1943–1991). Western Geography, 3, 71-83.

Reitan, C.H. (1974). Frequencies of Cyclones and Cyclogenesisfor North America, 1951–1970. Monthly Weather Review, 102,861–868.

268 Raphael

Schaefer, D.G. (1978). Climate. In K.W.G. Valentine, P.N.Sprout, T.E. Baker and L.M. Lavkulich (Eds.), The Soil Landscapes ofBritish Columbia (pp. 3-10). Victoria: British Columbia, Ministry ofthe Environment, Resource Analysis Branch.

Tuller, S.E. (1987). Climate. In C.N. Forward (Ed.), BritishColumbia: Its Resources and People. Victoria: Western GeographicalSeries Volume 22, Department of Geography, University ofVictoria.

Tyner, R.V. (1951). Paths taken by the Cold Air in Polar Outbreaksin British Columbia. Canada, Department of Transport, Meteo-rological Division, Local Forecast Study No. 14, Vancouver District.

Walker, E.R. (1961). A Synoptic Climatology for Parts of the WesternCordillera. Montreal: Arctic Meteorology Research Group, McGill Uni-versity, Publication in Meteorology No. 35.

The Clinate of the Central & Northern Interior of BC 269

270 Raphael

Appendix

The Clinate of the Central & Northern Interior of BC 271

272 Raphael

The Clinate of the Central & Northern Interior of BC 273

Tab

le 1

Loc

atio

n, p

erio

d o

f rec

ord

and

leng

th o

f rec

ord

for

clim

ate

stat

ions

in th

e st

udy

regi

on.

Stat

ion

Nam

eE

leva

tion

Per

iod

Leng

th o

f N

ame

Lati

tude

Long

itud

e(m

.a.s

.l.)

of

Rec

ord

Rec

ord

(Yea

rs)

Bar

kerv

ille

53°

04′

121°

31′

1265

1888

-199

210

4

Bur

ns L

ake

54°

14′

125°

46′

704

1969

-199

022

Dea

se L

ake

58°

25′

130°

00′

816

1947

-199

448

Fort

St.

Jam

es54

°27

′12

4°15

′69

518

95-1

994

100

Fort

St.

John

56°

14′

120°

44′

695

1942

-199

453

Fort

Nel

son

58°

50′

122°

35′

382

1938

-199

457

Ger

man

sen

Lan

din

g55

°47

′12

4°42

′74

719

52-1

992

43

Oot

sa L

ake

53°

46′

125°

58′

861

1956

-199

237

Prin

ce G

eorg

e53

°53

′12

2°40

′67

619

42-1

994

53

Que

snel

53°

02′

122°

31′

545

1946

-199

247

Smit

hers

53°

49′

127°

11′

523

1942

-199

453

Will

iam

s L

ake

52°

11′

122°

04′

940

1961

-199

434

274 Raphael

Tab

le 2

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r W

illia

ms

Lak

e (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

od 1

961-

1990

)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

3.0

-9.3

-5.1

-1.4

2.8

6.7

8.8

8.3

3.9

-0.1

-6.4

-11.

7-1

.4

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-4

.50.

65.

110

.515

.419

.422

.221

.916

.710

.31.

1-3

.99.

6

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-8.7

-4.3

-0.3

4.6

9.1

13.1

15.5

15.1

10.3

5.1

-2.6

-.7.7

4.1

Ext

rem

e m

onth

ly

min

imum

tem

pera

ture

(°C

)-4

2.2

-34.

6-3

1.7

-16.

7-5

.8-2

.20.

0-1

.7-8

.9-2

8.6

-41.

6-4

2.8

-42.

8

Dat

e19

6919

8919

7619

6619

8619

7319

7119

7319

7219

8419

8519

68/

28/

2/

3/

11/

14/

2/

2/

19/

27/

31/

27/

30

Ext

rem

e m

onth

ly

max

imum

tem

pera

ture

(°C

)12

.812

.817

.128

.834

.532

.234

.433

.335

.827

.116

.711

.235

.8

Dat

e19

6819

6319

9019

7719

8319

6919

7119

8119

8819

8719

7519

80/

20/

6/

29/

25/

29/

18/

31/

11/

4/

1/

4/

15

Mea

n m

onth

ly r

ainf

all (

mm

)3.

52.

83.

811

.333

.646

.351

.444

.635

.225

.58.

72.

026

8.8

Mea

n m

onth

ly s

now

fall

(cm

)44

.525

.918

.311

.12.

60.

30.

00.

0T1.

08.

131

.849

.119

2.8

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)38

.523

.219

.521

.536

.446

.751

.444

.636

.232

.935

.439

.942

6.0

The Clinate of the Central & Northern Interior of BC 275

Tab

le 3

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r Q

uesn

el (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

od19

61-1

990)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

3.6

-9.5

-5.3

-1.3

3.2

6.9

9.1

8.5

4.6

0.1

-5.7

-11.

5-1

.2

Mea

n m

onth

ly

max

imum

tem

pera

ture

(°C

)-4

.70.

96.

612

.917

.921

.524

.023

.518

.011

.12.

0-3

.610

.8

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-9.1

-4.2

0.7

5.8

10.5

14.2

16.6

16.1

11.3

5.7

-1.8

-7.5

4.9

Ext

rem

e m

onth

ly

min

imum

tem

pera

ture

(°C

)-4

6.7

-42.

2-3

8.9

-20.

0-1

0.0

-3.3

0.6

-1.7

-8.9

-28.

4-3

7.8

-41.

1-4

6.7

Dat

e 19

5019

5619

5519

5419

5419

5519

4919

4719

5119

8419

5519

68/

24/

15/

4/

4/

1/

7/

2/

20/

26/

31/

26/

30

Ext

rem

e m

onth

ly

max

imum

tem

pera

ture

(°C

)13

.915

.119

.431

.036

.535

.636

.736

.236

.126

.817

.212

.236

.7

Dat

e19

6819

8619

6019

7719

8319

6919

6119

9019

8819

8819

4919

52/

20/

25/

25/

25/

29/

18/

13/

5/

4/

4/

2/

13

Mea

n m

onth

ly r

ainf

all (

mm

)6.

17.

514

.118

.442

.056

.759

.056

.349

.044

.017

.36.

937

7.2

Mea

n m

onth

ly s

now

fall

(cm

)55

.825

.415

.34.

30.

40.

00.

00.

00.

35.

731

.950

.618

9.4

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)50

.528

.728

.222

.642

.556

.759

.056

.349

.349

.646

.049

.353

8.5

276 Raphael

Tab

le 4

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r B

arke

rvill

e (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

-od

196

1-19

90)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um te

mpe

ratu

re (°

C)-

14.0

-11.

3-9

.4-5

.0-0

.63.

15.

35.

11.

7-2

.3-9

.0-1

3.1

-4.1

Mea

n m

onth

ly m

axim

um te

mpe

ratu

re (°

C)-

4.5

-0.3

2.5

6.9

11.9

16.5

19.1

18.9

14.1

7.9

0.0

-4.2

7.4

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-9.2

-5.7

-3.3

1.0

5.7

9.8

12.2

12.1

7.9

2.9

-4.4

-8.6

1.7

Ext

rem

e m

onth

ly m

inim

um te

mpe

ratu

re (°

C)

-46.

7-4

3.3

-37.

2-2

6.1

-15.

0-6

.7-3

.9-7

.8-1

3.3

-30.

5-4

2.0

-41.

7-4

6.7

Dat

e19

4718

9319

5519

5419

4519

4519

4519

4719

2619

8419

8519

68/

31/

2/

4/

2/

1/

12/

4/

20/

23/

31/

27/

28

Ext

rem

e m

onth

ly m

axim

um te

mpe

ratu

re (°

C)

10.0

15.0

17.2

27.8

31.5

32.2

35.6

33.9

32.5

26.7

18.9

14.4

35.6

Dat

e19

8619

5419

3019

2619

8319

7819

4118

9719

8819

3518

9219

07/

13/

7/

28/

28/

29/

3/

17/

20/

4/

3/

3/

4

Mea

n m

onth

ly r

ainf

all (

mm

)6.

75.

77.

015

.158

.691

.194

.487

.982

.257

.313

.86.

652

6.4

Mea

n m

onth

ly s

now

fall

(cm

)97

.776

.169

.145

.713

.71.

00.

00.

03.

426

.285

.397

.351

5.5

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)10

4.6

81.8

76.0

60.8

72.3

92.0

94.4

87.9

85.6

83.6

99.1

103.

810

13.8

The Clinate of the Central & Northern Interior of BC 277

Tab

le 5

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r Pr

ince

Geo

rge

(All

dat

a ar

e th

e of

fici

al c

limat

e no

rmal

s fo

r th

epe

riod

196

1-19

90)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

4.1

-10.

3-6

.0-1

.42.

86.

48.

47.

73.

6-0

.1-6

.8-1

2.5

-1.9

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-5

.8-0

.74.

610

.816

.019

.722

.121

.416

.09.

80.

6-4

.59.

2

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-9.9

-5.4

-0.7

4.7

9.4

13.1

15.3

14.6

9.8

4.8

-3.1

-8.4

3.7

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-5

0.0

-45.

0-3

7.8

-25.

6-8

.3-2

.8-1

.7-3

.9-1

2.2

-26.

5-4

1.7

-45.

6-5

0.0

Dat

e 19

5019

5619

5519

5419

5419

4919

5019

7319

5119

8419

5519

64/

2/

15/

24/

4/

1/

26/

31/

19/

26/

31/

26/

16

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)12

.812

.817

.829

.736

.033

.934

.433

.431

.425

.217

.411

.736

.0

Dat

e19

8119

8619

6019

7719

8319

5819

6119

8119

8819

8719

8119

52/

22/

27/

20/

25/

29/

24/

13/

9/

4/

1/

11/

13

Mea

n m

onth

ly r

ainf

all (

mm

)5.

38.

212

.019

.549

.264

.560

.061

.258

.651

.416

.68.

741

5.2

Mea

n m

onth

ly s

now

fall

(cm

)60

.131

.625

.28.

82.

50.

00.

00.

00.

88.

0 42

.754

.123

3.8

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)54

.435

.034

.328

.351

.764

.560

.061

.259

.359

.452

.753

.861

4.7

278 Raphael

Tab

le 6

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r Fo

rt S

t. Ja

mes

(A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

od 1

961-

1990

)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

6.3

-12.

7-8

.5-2

.81.

96.

18.

27.

63.

5-0

.3-7

.1-1

4.1

-2.9

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-7

.2-2

.13.

49.

214

.919

.221

.821

.215

.89.

30.

1-5

.58.

3

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-11.

7-7

.3-2

.53.

38.

412

.715

.014

.49.

74.

5-3

.4-9

.72.

8

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-4

9.4

-49.

4-3

9.4

-29.

4-1

1.7

-6.1

-5.6

-7.8

-13.

3-2

3.0

-37.

8-4

7.2

-49.

4

Dat

e 19

2819

0719

0219

1119

5418

9519

3319

0019

2619

8418

9619

27/

1/

3/

15/

4/

1/

5/

29/

26/

23/

31/

20/

31

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)12

.013

.016

.724

.435

.033

.936

.735

.629

.626

.516

.111

.036

.7

Dat

e19

811

1986

1928

1934

1983

1950

1941

1939

1946

1987

1907

1980

/2

/27

/20

/25

/29

/18

/17

/9

/1

/1

/30

/15

Mea

n m

onth

ly r

ainf

all (

mm

)2.

63.

04.

913

.133

.944

.245

.944

.343

.232

.210

.53.

628

1.4

Mea

n m

onth

ly s

now

fall

(cm

)48

.026

.123

.46.

71.

10

00

0.5

7.5

33.0

48.8

195.

0

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)50

.629

.128

.319

.835

.044

.245

.944

.343

.739

.643

.652

.447

6.4

The Clinate of the Central & Northern Interior of BC 279

Tab

le 7

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r B

urns

Lak

e (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

-od

196

1-19

90)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)15

.4-1

3.3

-8.4

-2.8

2.0

5.5

7.5

7.0

3.8

0.1

-6.5

-14.

0-2

.9

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-5

.9-1

.24.

59.

714

.618

.420

.920

.515

.99.

60.

3-5

.28.

5

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-10.

6-7

.2-1

.93.

58.

312

.014

.213

.89.

94.

9-3

.0-9

.62.

9

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-4

6.7

-40.

0-4

0.0

-18.

9-7

.0-2

.2-0

.6-0

.8-8

.9-2

1.5

-37.

3-4

2.7

-46.

7

Dat

e 19

7219

7919

7619

7519

8619

7319

7319

8519

7219

8419

8519

84/

24/

14/

2/

5/

14/

10/

22/

25/

27/

31/

27/

31

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)11

.010

.315

.427

.334

.033

.332

.833

.430

.925

.614

.511

.334

.0

Dat

e19

811

1988

1979

1979

1983

1969

1971

1981

/9

1988

1987

1978

1980

/2

/20

/22

/28

/29

/11

/31

/9

/4

/1

/1

/15

Mea

n m

onth

ly r

ainf

all (

mm

)4.

82.

13.

511

.134

.148

.042

.641

.643

.136

.316

.63.

728

7.5

Mea

n m

onth

ly s

now

fall

(cm

)42

.527

.723

.15.

51.

10

00

0.6

7.4

34.4

44.7

187.

0

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)41

.126

.125

.416

.935

.148

.042

.641

.644

.043

.348

.643

.245

5.9

280 Raphael

Tab

le 8

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r O

otsa

Lak

e (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

-od

196

1-19

90)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

3.5

-11.

5-7

.9-2

.91.

45.

28.

08.

14.

61.

1-5

.0-1

0.6

-1.9

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-5

.0-0

.93.

37.

812

.816

.719

.719

.915

.69.

51.

4-3

.18.

1

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-9.2

-6.1

-2.3

2.4

7.1

11.0

13.9

14.0

10.1

5.3

-1.7

-6.8

3.1

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-4

2.2

-39.

0-3

4.4

-22.

2-6

.1-1

.7-1

.00.

6-5

.0-2

.1-3

6.0

-40.

0-4

2.2

Dat

e 19

7219

7919

6219

6319

5719

7719

8419

6919

6119

8419

8519

68/

25/

14/

3/

1/

22/

3/

6/

22/

26/

31/

27/

29

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)12

.212

.215

.024

.434

.031

.132

.833

.329

.025

.016

.711

.134

.0

Dat

e19

6819

6819

6219

7719

8319

6919

7119

6019

8819

8719

7819

56/

21/

27/

30/

24/

29/

17/

27/

9/

4/

1/

1/

26

Mea

n m

onth

ly r

ainf

all (

mm

)5.

43.

92.

59.

723

.638

.642

.738

.433

.331

.014

.16.

224

9.4

Mea

n m

onth

ly s

now

fall

(cm

)40

.522

.617

.76.

10.

80

00

0.4

5.3

31.8

41.3

166.

5

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)46

.026

.520

.215

.824

.538

.642

.738

.433

.836

.446

.347

.541

6.6

The Clinate of the Central & Northern Interior of BC 281

Tab

le 9

Tem

pera

ture

and

pre

cipi

tati

on s

tati

stic

s fo

r Sm

ithe

rs (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

od19

61-1

990)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

3.0

-9.6

-5.7

-1.5

2.6

5.9

8.3

7.8

4.0

0.3

-5.7

-11.

7-1

.5

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-5

.2-0

.14.

810

.315

.319

.021

.421

.015

.79.

00.

6-4

.49.

0

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-9.0

-4.8

-0.4

4.4

9.0

12.5

14.9

14.4

9.8

4.7

-2.5

-8.0

3.8

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-4

3.9

-35.

6-3

3.3

-18.

3-7

.2-4

.1-1

.1-2

.2-6

.7-2

2.0

-32.

4-3

6.7

-43.

9

Dat

e 19

5019

5619

5519

4819

5419

8819

4719

4819

4819

841

1985

1968

/13

/15

/3

/4

/1

/2

/2

/28

/23

/3

/27

/29

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)15

.611

.916

.024

.335

.833

.934

.435

.231

.124

.415

.611

.535

.8

Dat

e19

6319

9019

8619

7919

8319

6919

7119

9019

8819

8719

6719

80/

6/

22/

20/

28/

30/

11/

30/

12/

3/

1/

21/

15

Mea

n m

onth

ly r

ainf

all (

mm

)11

.66.

35.

812

.132

.742

.245

.742

.153

.555

.522

.37.

533

7.4

Mea

n m

onth

ly s

now

fall

(cm

)60

.729

.719

.76.

90.

90.

00.

00.

00.

27.

339

.251

.921

6.4

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)57

.829

.322

.318

.033

.542

.245

.742

.153

.762

.354

.548

.050

9.5

282 Raphael

Tab

le 1

0Te

mpe

ratu

re a

nd p

reci

pita

tion

sta

tist

ics

for

Ger

man

sen

Lan

din

g (A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

od 1

961-

1990

)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-2

0.3

-15.

5-1

1.0

-4.3

0.3

4.6

6.8

5.8

1.9

-2.1

-10.

9-1

8.7

-5.3

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-1

0.6

-3.9

2.7

8.6

14.1

18.4

20.8

20.0

14.5

6.6

-3.5

-9.8

6.5

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-15.

3-9

.7-4

.12.

27.

211

.513

.812

.98.

22.

3-7

.2-1

4.1

0.6

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-4

8.8

-44.

4-4

1.1

-26.

1-1

2.8

-3.3

-2.2

-3.9

-12.

5-3

0.0

-39.

5-4

5.8

-48.

8

Dat

e 19

7919

5619

7619

5419

5419

7419

6319

6919

8319

5119

8519

78/

15/

15/

2/

4/

1/

4/

27/

23/

28/

31/

27/

31

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)11

.711

.115

.627

.034

.532

.232

.833

.029

.523

.011

.79.

734

.5

Dat

e19

6319

5419

6519

7719

8319

6919

7119

9019

8819

8719

6919

80/

6/

2/

10/

25/

29/

16/

30/

12/

4/

1/

2/

15

Mea

n m

onth

ly r

ainf

all (

mm

)1.

81.

42.

513

.338

.558

.155

.946

.345

.632

.66.

01.

330

3.3

Mea

n m

onth

ly s

now

fall

(cm

)52

.334

.929

.112

.02.

20.

30.

00.

02.

015

.949

.555

.225

3.4

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)43

.829

.125

.522

.840

.558

.455

.946

.346

.946

.945

.446

.450

7.9

The Clinate of the Central & Northern Interior of BC 283

Tab

le 1

1Te

mpe

ratu

re a

nd p

reci

pita

tion

sta

tist

ics

for

Dea

se L

ake

(All

dat

a ar

e th

e of

fici

al c

limat

e no

rmal

s fo

r th

e pe

ri-

od 1

961-

1990

)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-2

2.5

-18.

5-1

3.1

-5.8

-0.8

3.3

5.8

4.9

1.2

-3.2

-14.

0-2

0.4

-6.9

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-1

3.1

-6.9

0.0

6.6

12.7

17.2

19.2

18.1

12.8

5.7

-5.2

-11.

74.

6

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-17.

7-1

2.6

-6.5

0.4

6.0

10.3

12.6

11.5

7.0

1.3

-9.5

-16.

0-1

.1

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-5

1.2

-48.

3-4

2.8

-31.

7-1

1.1

-5.6

-2.2

-6.1

-15.

0-2

7.3

-42.

5-4

6.1

-51.

2

Dat

e 19

4719

6819

5519

4819

7219

5219

7619

5019

5119

8419

8519

49/

31/

2/

3/

2/

1/

15/

17/

15/

26/

29/

26/

29

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)8.

911

.712

.822

.235

.333

.931

.732

.228

.920

.614

.47.

835

.3

Dat

e19

5819

6819

6219

7619

8319

5019

5119

7119

6719

4819

4919

85/

6/

27/

30/

30/

30/

18/

10/

1/

17/

1/

2/20

Mea

n m

onth

ly r

ainf

all (

mm

)0.

80.

00.

32.

025

.142

.559

.752

.848

.719

.92.

60.

525

5.0

Mea

n m

onth

ly s

now

fall

(cm

)41

.232

.327

.714

.65.

60.

31.

00.

01.

417

.940

.844

.222

7.1

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)29

.823

.319

.713

.630

.242

.960

.752

.950

.035

.630

.932

.142

1.6

284 Raphael

Tab

le 1

2Te

mpe

ratu

re a

nd p

reci

pita

tion

sta

tist

ics

for

Fort

St.

John

(A

ll d

ata

are

the

offi

cial

clim

ate

norm

als

for

the

peri

od 1

961-

1990

)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-1

9.4

-15.

6-1

0.4

-1.9

3.8

8.0

10.1

9.0

4.3

-0.1

-11.

0-1

7.4

-3.4

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-1

0.8

-6.5

-0.6

8.8

15.5

19.4

21.5

20.3

14.8

8.7

-3.3

-9.1

6.6

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-15.

0-1

1.0

-5.5

3.5

9.7

13.7

15.8

14.7

9.6

4.3

-7.1

-13.

21.

6

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-4

7.2

-42.

2-3

6.7

-28.

9-1

0.6

-0.6

2.2

-1.2

-12.

8-2

5.0

-39.

2-4

0.6

-47.

2

Dat

e 19

4719

4719

5519

5419

5919

5119

7519

7719

7419

8419

8519

48/

30/

1/

3/

1/

1/

25/

30/

31/

30/

31/

26/

8

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)10

.612

.813

.927

.931

.831

.733

.333

.630

.025

.618

.311

.433

.6

Dat

e19

6519

6819

6619

7719

8319

7019

4419

8119

4419

4319

4919

80/

15/

27/

28/

25/

29/

3/

19/

9/

9/

2/

3/

15

Mea

n m

onth

ly r

ainf

all (

mm

)0.

70.

20.

87.

334

.166

.573

.756

.739

.712

.82.

60.

729

5.9

Mea

n m

onth

ly s

now

fall

(cm

)35

.928

.428

.314

.06.

60.

40

0.8

4.3

15.1

29.6

34.8

198.

2

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)30

.823

.524

.120

.840

.967

.073

.757

.543

.927

.128

.829

.446

7.5

The Clinate of the Central & Northern Interior of BC 285

Tab

le 1

3Te

mpe

ratu

re a

nd p

reci

pita

tion

sta

tist

ics

for

Fort

Nel

son

(All

dat

a ar

e th

e of

fici

al c

limat

e no

rmal

s fo

r th

e pe

ri-

od 1

961-

1990

)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

.N

ovD

ecA

nnua

l

Mea

n m

onth

ly m

inim

um

tem

pera

ture

(°C

)-2

6.5

-22.

3-1

5.4

-4.2

2.9

8.3

10.4

8.6

2.7

-4.0

-17.

6-2

4.5

-6.8

Mea

n m

onth

ly m

axim

um

tem

pera

ture

(°C

)-1

7.7

-11.

0-2

.38.

516

.221

.223

.021

.214

.96.

0-9

.2-1

7.6

4.5

Mea

n m

onth

ly te

mpe

ratu

re (°

C)

-22.

0-1

6.5

-8.8

2.2

9.6

14.8

16.7

14.9

8.8

1.0

-13.

3-2

0.3

-1.1

Ext

rem

e m

onth

ly m

inim

um

tem

pera

ture

(°C

)-5

1.7

-48.

3-3

9.4

-34.

4-1

5.0

-1.1

1.1

-3.3

-16.

7-2

8.6

-41.

1-4

7.8

-51.

7

Dat

e 19

4719

4719

5519

5419

7419

5719

5319

8219

7419

8419

6319

38/

30/

2/

3/

2/

2/

10/

28/

26/

30/

30/

22/

29

Ext

rem

e m

onth

ly m

axim

um

tem

pera

ture

(°C

)10

.715

.017

.827

.332

.133

.936

.734

.432

.825

.618

.310

.736

.7

Dat

e19

8119

6819

6619

7719

8319

6919

4219

8119

3819

4319

6919

85/

19/

29/

29/

24/

29/

15/

1/

8/

2/

6/

2/

25

Mea

n m

onth

ly r

ainf

all (

mm

)0.

30.

20.

35.

241

.164

.283

.763

.138

.48.

01.

00.

230

5.7

Mea

n m

onth

ly s

now

fall

(cm

)29

.721

.824

.919

.57.

70.

10.

00.

25.

025

.729

.627

.019

1.2

Mea

n m

onth

ly to

tal p

reci

pita

tion

(mm

)21

.816

.217

.220

.247

.764

.383

.763

.343

.130

.821

.518

.744

8.5

286 Raphael

Tab

le 1

4Pr

ecip

itat

ion

extr

emes

and

oth

er s

tati

stic

s fo

r th

e tw

elve

sta

tion

s in

the

stu

dy

regi

on. (

All

valu

es i

n (m

m)

exce

pt fo

r th

e co

effi

cien

t of v

aria

tion

.)

Stat

ion

Per

iod

Coe

ffici

ent o

fSt

anda

rdM

ean

Rec

ord

Year

Rec

ord

Year

Var

iati

onD

evia

tion

Low

Hig

h

Bar

ker

vill

eA

nnua

l0.

1919

3.7

1028

.252

3.6

1896

1860

.719

48

Spri

ng0.

2959

.520

6.1

90.9

1895

449

1948

Sum

mer

0.3

83.6

277

98.1

1896

620.

319

48

Fall

0.25

68.6

270.

111

6.1

1976

455

1947

Win

ter

0.39

106.

627

5.1

85.4

1903

612.

219

47

Fort

St.

Jam

esA

nnua

l0.

2190

.743

5.8

266.

719

1673

8.5

1959

Spri

ng0.

3727

73.3

18.6

1909

163.

619

60

Sum

mer

0.36

45.6

127.

833

.119

2227

2.3

1957

Fall

0.3

35.8

118.

451

.319

0022

6.3

1959

Win

ter

0.35

40.3

116.

242

.119

1623

8.7

1982

Bu

rns

Lak

eA

nnua

l0.

1360

.45

5.5

334.

319

8560

8.8

1971

Spri

ng0.

2619

.977

.329

.519

8311

8.8

1986

Sum

mer

0.28

37.5

132.

159

.919

7422

119

76

Fall

0.21

2813

5.8

66.2

1979

204.

519

75

Win

ter

0.35

3911

0.3

43.2

1991

211.

119

72

The Clinate of the Central & Northern Interior of BC 287

Tab

le 1

4co

ntin

ued

Stat

ion

Per

iod

Coe

ffici

ent o

fSt

anda

rdM

ean

Rec

ord

Year

Rec

ord

Year

Var

iati

onD

evia

tion

Low

Hig

h

Dea

se L

ake

Ann

ual

0.17

68.3

411.

829

6.5

1951

574

1962

Spri

ng0.

3621

.459

16.8

1945

111.

419

81

Sum

mer

0.29

44.8

152.

759

.219

9232

9.2

1962

Fall

0.31

35.7

115.

260

.519

5723

9.9

1986

Win

ter

0.32

27.2

84.8

22.9

1969

145.

819

67

Ger

man

sen

Lan

din

gA

nnua

l0.

1680

.951

3.4

334.

819

7068

3.4

1987

Spri

ng0.

434

.787

.133

.519

9117

3.4

1988

Sum

mer

0.32

50.8

159

76.7

1967

291.

119

57

Fall

0.2

27.1

137.

883

.818

7019

3.5

1986

Win

ter

0.27

35.2

129.

460

.519

7819

7.6

1959

Fort

St.

Joh

nA

nnua

l0.

2194

.145

5.5

251.

319

4562

0.7

1972

Spri

ng0.

432

.281

.520

.619

4515

0.8

1964

Sum

mer

0.38

7319

2.6

88.4

1945

361.

519

87

Fall

0.36

34.3

95.6

27.4

1943

204.

319

57

Win

ter

0.38

3385

.929

.919

8714

4.7

1963

288 Raphael

Tab

le 1

4co

ntin

ued

Stat

ion

Per

iod

Coe

ffici

ent o

fSt

anda

rdM

ean

Rec

ord

Year

Rec

ord

Year

Var

iati

onD

evia

tion

Low

Hig

h

Dea

se L

ake

Ann

ual

0.17

68.3

411.

829

6.5

1951

574

1962

Fort

Nel

son

Ann

ual

0.19

84.1

438.

729

9.2

1938

682.

819

62

Spri

ng0.

4234

.583

23.3

1985

182.

719

88

Sum

mer

0.37

73.1

198.

677

.219

3945

0.8

1976

Fall

0.3

2893

.434

.819

4318

8.2

1944

Win

ter

0.45

28.5

63.7

30.6

1984

148.

319

47

Oot

sa L

ake

Ann

ual

0.19

80.8

423.

525

4.5

1986

588.

319

57

Spri

ng0.

2421

.664

21.6

1973

120.

719

57

Sum

mer

0.4

4912

2.2

47.2

1970

203.

719

57

Fall

0.28

32.2

115.

458

.319

7921

7.6

1975

Win

ter

0.33

39.8

121.

977

.319

7524

4.1

1958

Pri

nce

Geo

rge

Ann

ual

0.15

92.9

609.

844

3.6

1943

843.

719

64

Spri

ng0.

2425

.910

7.2

67.3

1983

153.

219

84

Sum

mer

0.3

5718

8.7

9519

6731

8.1

1983

Fall

0.26

43.5

166.

681

.819

4326

619

92

Win

ter

0.28

40.9

147.

379

.819

8325

6.3

1982

The Clinate of the Central & Northern Interior of BC 289

Tab

le 1

4co

ntin

ued

Stat

ion

Per

iod

Coe

ffici

ent o

fSt

anda

rdM

ean

Rec

ord

Year

Rec

ord

Year

Var

iati

onD

evia

tion

Low

Hig

h

Dea

se L

ake

Ann

ual

0.17

68.3

411.

829

6.5

1951

574

1962

Qu

esn

elA

nnua

l0.

1686

.153

6.4

283.

519

8772

4.1

1948

Spri

ng0.

2723

.688

.335

.819

8513

5.3

1980

Sum

mer

0.33

57.8

177.

763

.519

5131

0.9

1948

Fall

0.32

43.9

137.

460

.419

8724

6.4

1961

Win

ter

0.32

42.9

133

48.1

1987

223.

219

72

Sm

ith

ers

Ann

ual

0.16

82.3

513

311.

219

4475

919

47

Spri

ng0.

3123

.977

.737

1956

149.

619

93

Sum

mer

0.32

41.6

130.

452

.919

9224

6.5

1993

Fall

0.25

41.5

168.

269

.919

4328

7.9

1991

Win

ter

0.35

47.8

136.

764

.319

7031

3.2

1947

Wil

liam

s L

ake

Ann

ual

0.21

89.8

424.

123

2.9

1970

633.

419

82

Spri

ng0.

3627

.676

.839

.919

7014

8.9

1980

Sum

mer

0.43

61.6

144.

533

.319

6129

1.1

1982

Fall

0.35

36.1

103.

137

1987

199.

319

85

Win

ter

0.37

36.8

99.7

44.2

1983

183.

719

70