Spring warmth coming to Pacific Northwest next week
Astronomical Spring begins on March 20 in the Northern Hemisphere and the first glimpse of warmth will come shortly afterward to the Pacific Northwest. A strong upper level ridge is forecast to develop in the Western United States and Canada, bringing warm weather Monday through Wednesday.
This warm spell will be the first shot at 70ºF (21ºC) temperatures for many lowland locations in Washington and Oregon. Somewhere in the Portland metro may even tap 80ºF (26ºC) on Tuesday. A few inland locations in British Columbia could reach 20ºC (68ºF) but most areas will be slightly below that.
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The first “heat wave” of the season will be preceded by very active weather conditions. Rain and mountain snow are likely Thursday through the weekend with the storm track aimed near Washington.
Most precipitation will fall in and west of the Cascades but the Columbia Basin will see isolated rain showers for the entire period. The best chance of rain in the Tri-Cities is on Friday.
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The storm track shifts toward the northern end of Vancouver Island early next week. Leftover showers may be observed around and north of Seattle on Monday as it moves northward. Since it will only move to around Port Hardy, communities like Prince George will largely miss out on the heat wave.
Annotated 850 mb temperature and wind for midday Tuesday. (Windy)
Under the upper level ridge, warm air will be pulled northward into the Pacific Northwest from Arizona and Southern California. This will raise temperatures aloft allowing surface temperatures to climb Monday through Wednesday. Mostly sunny skies can be expected south of the storm track.
An active weather pattern continues afterward so that this first taste of Spring warmth will be short lived. Current indications are that the next regional system will move into the region Thursday as the ridge moves eastward and an upper level low takes its place.
Weak thunderstorms are common in the Northwest because while surface temperatures are warming this is actually the coldest time of year in the upper levels. That combination of warm surface temperatures and cold temperatures aloft enhances upward movement, allowing more moisture to be transported upward to form thunderstorms.
850 mb temperatures and surface precipitation on the ECMWF ensemble for Pasco, Washington. (Wetterzentrale)
There isn’t a strong signal for another early-season “heat wave” within the next 15 days. Frontal passages followed by weak thunderstorms before the following front appear to be the primary weather pattern other than the first half of next week.
Thanks to the Cascade rain shadow, most of the Columbia Basin will likely be dry with sunshine in between fronts. That said, that area will see several windy days as well as weather patterns work their way across the mountains.
Senter Falls, Lyndeborough NH
