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March 10, 2021 – Winter storm to bring mountain and foothill snow, Valley rain, and thunderstorms through today. Dry and milder weather expected to return by the end of the week. Next chance for precipitation may be Sunday into Monday.

Discussion

Satellite imagery this morning shows the closed low just off of the northwest coast of CA this morning. Stratiform rain is pushing eastwards and into the the foothills and mountains of the Sierra. Snow levels have fallen to roughly 3000 to 3500 feet this morning and may drop down to 2500 feet at some locations. Behind the stratiform rain, satellite and radar imagery shows precip in the form of showers. The low is still forecast to move onshore near central CA which will keep showers in the area through the afternoon and evening hours. CAMS still favor some thunderstorm development today for the Valley and foothills, with guidance favoring areas south of Red Bluff and Chico. Stronger cells may produce small hail and perhaps even some funnel clouds or a brief weak tornado. Shear profiles don’t look as favorable today for tornado activity, but there is still a small chance. PWATS still favor low moisture, with values generally less than a half inch which limit any potential for debris flow issues with recent burn scars.

Tonight, as the low drops south, skies should begin to clear. Behind it high pressure will start to nudge into NorCal. This should allow for light north winds to develop. Current thinking is that the winds will stretch from Redding down to Sacramento and Solano counties. This should limit fog and stratus development; however, south of there winds may remain light enough to support low cloud and patchy fog to develop. HREF guidance and NAM soundings support low cloud development, but suppress fog formation. Should clouds form overnight they’ll be short lived as north winds will become more widespread. Most areas will remain dry for Thursday with the exception being over the Sierra where showers could develop. Dry weather then continues into Friday for all of interior NorCal.

Colder morning lows in the 30s in the Valley and 20s to 30s in the foothills expected Thursday and Friday mornings as skies clear. The exception may be where any low cloud forms and limits radiational cooling. High temperatures return to the 60s across the Valley.

Extended discussion (Sunday through Wednesday)

Ensembles continue to struggle with the timing and strength of the next trough early next week (Sunday-Monday), though cluster analysis hints at potential for another colder system with widespread showers (nearly 50% of the members now indicate a deeper trough over NorCal on Monday).

Drier weather expected Tuesday, then showers potentially return Wednesday (though very low confidence currently on another trough approaching). Temperatures forecast to be a little below average with the coolest day on Monday.