seasonal climate forecast verification: april-june · pdf filenanalog years varied from cool...

Contact: Pete Parsons, ODF Meteorologist503-945-7448 or peter.gj.parsons@oregon.gov

Oregon Dept. of Agriculture (ODA) - Oregon Dept. of Forestry (ODF).ODA Production support from Diana Walker, Jacob Cruser, and Andy Zimmerman

Seasonal Climate Forecast VerificationJanuary – March 2018

Issued: April 11, 2018

Format and Purpose:n A side-by-side comparison of the “Seasonal Climate Forecast” vs. what (Actually Occurred) is done for both the 1-month & 3-month forecasts.*n The accuracy of each forecast is reviewed, and the need for analog-year updates is examined.n This is part of an ongoing assessment of the utility of this forecast method.**

*Utilizes 1981-2010 long-term averages

**See “Forecasting Methods…” at:https://oda.direct/Weather

January 2018(Forecast Issued December 22, 2017)/(Actual)

Forecast Upper-Air Anomalies Actual Upper-Air Anomalies

n Both the predicted upper-air pattern (left) and the observed pattern (right) showed a highly anomalous jet stream configuration (typical of La Niña). However, their respective patterns were out-of-phase with each other. Mostly a forecast “miss,”

Actual Temperatures

Data courtesy of the National Centers for Environmental Information (NCEI)

Forecast Temperatures

January 2018(Forecast Issued December 22, 2017)/(Actual)

Forecast Precipitation Actual Precipitation

Data courtesy of the National Centers for Environmental Information (NCEI)

January 2018(Forecast Issued December 22, 2017)/(Actual)

n Near or below-average temperatures, due to a greater-than-average chance of cold spells. (Persistent upper-level ridging kept cold Arctic air masses east of the Rockies. As a result, temperatures were quite mild, ranging from 2-3°F above average west to more than 5°F above average east.) A forecast “miss.”

n A continuation of drier-than-average conditions was favored, with below-average mountain snowfall. (The same upper-level ridging that sent cold air dumps east of the Rockies also weakened and deflected storms, as they approached the west coast. Precipitation and mountain snowfall was below average.) A forecast “hit.”

January 2018(Forecast Issued December 22, 2017)/(Actual)

February 2018(Forecast Issued January 19, 2018)/(Actual)

Forecast Upper-Air Anomalies Actual Upper-Air Anomalies

n A highly anomalous pattern was accurately predicted. The persistent west coast ridge retrograded (moved westward), into the Gulf of Alaska, for the second half of the month...bringing quite cold temperatures and valley snow. Mostly a forecast “hit.”

February 2018(Forecast Issued January 19, 2018)/(Actual)

Forecast Temperatures Actual Temperatures

Data courtesy of the National Centers for Environmental Information (NCEI)

Forecast Precipitation Actual Precipitation

Data courtesy of the National Centers for Environmental Information (NCEI)

February 2018(Forecast Issued January 19, 2018)/(Actual)

n The forecast graphics skewed cool and wet due to a very cold 1963 and very wet 1996, but many flavors of highly anomalous weather were possible. (Highly anomalous weather dominated the month…the first half was very warm and dry, and the second half was very cold with significant mountain snow.) The forecast accurately predicted “highly anomalous” conditions but struggled with specifics.

n Some recovery in mountain snowpacks, although likely staying below average, due to a slow start… (The second half of the month brought very low snow levels, down to sea level at times, and some recovery to mountain snowpacks, especially north. However, precipitation was slightly below average.) Mostly a forecast “hit.”

February 2018(Forecast Issued January 19, 2018)/(Actual)

March 2018(Forecast Issued February 16, 2018)/(Actual)

Forecast Upper-Air Anomalies Actual Upper-Air Anomalies

n Colder-than-average air aloft over the Pacific Northwest was both predicted (left panel) and observed (right panel). The large positive (warm) anomaly in the western Gulf of Alaska was also accurately predicted. A forecast “hit.”

Forecast Temperatures Actual Temperatures

Data courtesy of the National Centers for Environmental Information (NCEI)

March 2018(Forecast Issued February 16, 2018)/(Actual)

Forecast Precipitation Actual Precipitation

Data courtesy of the National Centers for Environmental Information (NCEI)

March 2018(Forecast Issued February 16, 2018)/(Actual)

n Below-average temperatures expected. (Temperatures ranged from 1.2°F to 2.1°F below average statewide.) A forecast hit.

n Slightly-below-average precipitation... (Precipitation was near or slightly below average.) A forecast hit.

n Some recovery of mountain snowpacks expected, relative to average. (Mountain snowpacks generally showed a 5-10 % recovery, relative to average, but remained below average for the season.) A forecast hit.

March 2018(Forecast Issued February 16, 2018)/(Actual)

January – March 2018(Forecast Issued December 22, 2017)/(Actual)

Forecast Upper-Air Anomalies Actual Upper-Air Anomalies

n A strong positive anomaly was both predicted (left panel) and observed (right panel), in the western Gulf of Alaska, which is typical of La Niña. Weak anomalous troughing was also accurately depicted over the Pacific Northwest. A “forecast hit.”

Forecast Temperatures Actual Temperatures

Data courtesy of the National Centers for Environmental Information (NCEI)

January – March 2018(Forecast Issued December 22, 2017)/(Actual)

Forecast Precipitation Actual Precipitation

Data courtesy of the National Centers for Environmental Information (NCEI)

January – March 2018(Forecast Issued December 22, 2017)/(Actual)

n Although La Niña winters tend to be relatively cool and damp for Oregon, this year’s analogs showed more-average conditions. (Month-to-month weather was highly anomalous and variable. The 3-month period displayed slightly-below-average temperatures west and slightly-above-average temperatures east. Precipitation ranged from near to slightly-below average. Mountain snowpacks started out well-below average but recovered later in the period…see next few slides.) Monthly forecasts struggled with the highly-anomalous and variable conditions experienced in January and February, before turning quite accurate in March. A general forecast “hit” for the 3-month period.

January – March 2018(Forecast Issued December 22, 2017)/(Actual)

Contact: Pete Parsons, ODF Meteorologistat 503-945-7448 or peter.gj.parsons@oregon.gov

Updated Mid-Month

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