Thu Nov 23 12GMT… OVER ALBERTA... MOST OF RGN ENTRENCHED IN ARCTIC AIRMASS WITH FNT EXPECTED TO MEANDER VICINITY THE US BORDER FOR NEXT 36 HRS. DEPTH OF COLD AIR OVR CENTRAL ALBERTA BETWEEN 850 AND 700MB.

MODELS FCSTG INVERTED TROF OVER CENTRAL AND EASTERN AREAS WITHWATER EQUIVALENT AMOUNTS OF 5 TO 8 WHICH GIVEN THE COLD TEMPERATURES OUGHT TO TRANSLATE TO 8-12 CM WORTH OF SNOW. THIS SEEMS REASONABLE AND CONSIDERING WINTER STORM WATCH FOR RGNS JUST EAST OF EDMNONTON.

• deep saturated stable layer• wind shear

Stony Plain 12Z Thurs 23 Nov. 2006

Nov. 24: Weather discussion …Thurs 23rd into Fri 24th

MST T Td

13:00 Light Snow -17 -20

12:00 Light Snow -17 -20

11:00 Light Snow -17 -19

10:00 Light Snow -17 -19

09:00 Light Snow -17 -19

08:00 Light Snow -17 -19

07:00 Cloudy -17 -19

06:00 Light Snow -17 -19

05:00 Cloudy -15 -19

04:00 Cloudy -15 -18

03:00 Cloudy -15 -19

02:00 Light Snow -16 -18

01:00 Cloudy -15 -18

00:00 Cloudy -15 -18

12Z Thurs 23 Nov.

Max available 0.2 – 0.4 inches water 0.5 – 1 cm waterSnow equivalent is 10-15 times deeper, so (taking 15x)we could get a max of 15 cm or (taking 10x) a min of 5 cm(… this assumes 100% conversion to snow on ground)

Thu Nov 23 19Z 2006 GMT.. SNOW FALLING ACROSS CENTRAL ALBERTA COURTESY OF AN UPPER LOW WITH LOTS OF INSTABILITY**. AMOUNTS SO FAR SEEM TO BE IN THE 4 TO 8 CMRANGE ALTHOUGH AS THE SYSTEM MOVES NORTH AND UPPER LOW DEVELOPS, THE SPEED OF THE SYSTEM WILL DIMINISH AND LARGER AMOUNTS ARE EXPECTED. SO FAR SEEMS TO BE A 15 TO 1 SWE.

GEM 36 hr prog from 12Z Wed giving 12 hr cumulative precip (mm water equiv). Thus GEM predicted about 1-3 mm SWE (snow water equivalent) ie. 1.5-4.5 cm snow for 05-17 MST Thurs

** let’s see what this refers to…

x by 15 to convert to snow: 1.5 cm… seems too low

• on first sight, we noted the deep saturated stable layer

• so where’s the “lots of instability”?

Stony Plain 12Z Thurs 23 Nov. 2006

This little nose of colder air above ground?

Note lapse rate is (roughly) dry adiabatic in thin layer on ground…

Kelowna (B.C.)

Peaks about 3 km ASL

inversion

MST T Td

18:00 Light Snow -17 -20

17:00 Light Snow -17 -19

16:00 Light Snow -17 -20

15:00 Light Snow -17 -20

14:00 Cloudy -17 -20

13:00 Light Snow -17 -20

12:00 Light Snow -17 -20

11:00 Light Snow -17 -19

10:00 Light Snow -17 -19

09:00 Light Snow -17 -19

08:00 Light Snow -17 -19

07:00 Cloudy -17 -19

06:00 Light Snow -17 -19

05:00 Cloudy -15 -19

04:00 Cloudy -15 -18

03:00 Cloudy -15 -19

02:00 Light Snow -16 -18

01:00 Cloudy -15 -18

00:00 Cloudy -15 -18

MST T Td

18:00 Light Snow -17 -20

17:00 Light Snow -17 -19

16:00 Light Snow -17 -20

15:00 Light Snow -17 -20

14:00 Cloudy -17 -20

13:00 Light Snow -17 -20

12:00 Light Snow -17 -20

11:00 Light Snow -17 -19

10:00 Light Snow -17 -19

09:00 Light Snow -17 -19

08:00 Light Snow -17 -19

07:00 Cloudy -17 -19

06:00 Light Snow -17 -19

05:00 Cloudy -15 -19

04:00 Cloudy -15 -18

03:00 Cloudy -15 -19

02:00 Light Snow -16 -18

01:00 Cloudy -15 -18

00:00 Cloudy -15 -18

12 hr fcst valid 00Z Friday givingfcst snow accumulation for 21Z Thurs - 00Z Fri [ x by 2.5 to get cm](Edmonton in the 0.5 – 1 inch band, ie. about 1-3 cm)

3 hr fcst valid 15Z Thurs giving fcst snow accumulation for 12Z Thurs - 15Z Thurs Did not predict snow for Edmonton

http://www.weather.unisys.com/nam/winter.html

24 hr prog from 12Z Wed

CMC 500 mb analysis 12Z Thurs 23 Nov. 2006

48 hr prog from 12Z Tues

• 24 hr prog excellent• 48 hr prog v.g. too

CMC 500 mb analysis 12Z Thurs 23 Nov. 2006

• GOES seeing high (cold) cloud tops in Ab.• red arrows show wind above 500 mb level (where it was

more southerly than at 500 mb – see sounding)• upper wind orientation backing to S through morning• Edmonton thickness 522 dam

400 – 100 mb level700 – 400 mb level1000 – 700 mb level

GOES satellite winds12Z Thurs 23 Nov.

GOES satellite winds18Z Thurs 23 Nov.

CMC 850 mb analysis 12Z Thurs 23 Nov. 2006

• strong T-gradient against mountains

CMC sfc analysis 12Z Fri 24 Nov.

• sfc ridge through C. Ab., p rising• sfc temps rather uniform• mid morning, only partial cover of light cloud• windy – trees moving, snow blowing off rooves• reasonably strong sfc p-gradient

CMC 850 mb analysis 12Z Fri 24 Nov.

• deep inversion • baroclinic zone remains against mntns

CMC 500 mb analysis 12Z Fri 24 Nov.

• closed upper low (meriodional flow)• main stream far to south• setting is a broad longwave trough over W North Am.• cold thickness advection• erroneous wind direction!• Edmonton thickness 510 dam (down 12 dam = 6 degrees since 12Z Thurs)

GEM 0hr prog valid 12Z Fri

GEM 48hr prog valid 12Z Sunday

• Edmonton thickness 494 dam

• ie. 8 degrees colder yet

Extended forecasts for Sunday Monday and Tuesday for central and northern Alberta issued by Environment Canada at 10.30 AM MST Friday 24 November 2006.

City of Edmonton…

Sunday..Cloudy with 60 percent chance of flurries. Low minus 28. High minus 24.

Monday..Cloudy with 60 percent chance of flurries. Low minus 26. High minus 24.

Tuesday..Sunny. Low minus 27. High minus 21.

Normals for the period..Low minus 13. High minus 3.