March 26, 2020 – Threat of showers or isolated afternoon thunderstorms continues today over mainly the Motherlode and Sierra Nevada, otherwise drier weather into Friday. Showers with mountains snow showers returns this weekend, then drier and warmer weather expected early next week.
Discussion
Upper trough axis continues to slowly shift south through NorCal today, pushing south of the CWA this afternoon. Models keep a threat of associated showers today over southern portions of the forecast area with best chances over the Motherlode and Sierra Nevada. Enough model CAPE and instability depicted in these areas this afternoon to include a slight chance of isolated thunderstorms. Snow levels rise from the foothills this morning to around 4000 feet this afternoon. Light additional snow accumulations expected. Drier weather develops over the northern half of the CWA as upper ridging from the EPAC begins to build inland.
Shower threat expected to end this evening. Clearing skies with colder AMS in place will result in some areas in the Central Valley near freezing overnight with patchy morning frost. Colder mountain valleys could see the mercury drop into the teens and single digits overnight.
Drier weather forecast across interior NorCal Friday under upper level ridging. This is short-lived though as models indicate next Pacific low approaching NW CA Friday afternoon into evening. Widespread shower threat with mountain snow returns this weekend as upper low weakens to trough, moving inland late Saturday. Another upper trough progged to follow it Sunday. Overall weekend QPF looks light with locally moderate precipitation possible over the mountains. Snow levels begin around 3000 to 4000 feet Saturday morning, rising to 4000 to 5000 feet Saturday afternoon into evening with little change into Sunday.
Upper troughing shifts south and east of the area Sunday evening with shower threat ending. EPAC upper ridging then begins to build inland returning drier weather with warming temperatures early next week.
Extended discussion (Monday through Thursday)
Overall quiet weather is expected for the extended period. A trough will be pushing into BC on Monday/Tuesday and that will push a cold front south through the PacNW. There is model disagreement on how far south this trough and cold front make it. Both EC and GEFS ensembles are further north with it than the deterministic runs but the EC ensemble is further north then the GEFS ensemble. The 12z WPC clusters are showing a trend of higher heights over NorCal. This would support a drier forecast but some light showers still look to be possible in the coastal range and northern Shasta County mountains Monday and Tuesday. Weak ridging builds in Wednesday and continues into the end of the period. Highs will be near average to begin the week but will warm to above average by Wednesday.