April 24, 2021 – Light scattered showers mainly north of I-80 through this afternoon. A winter storm will bring widespread rain and impactful mountain snow tonight through Sunday with mountain showers lingering into Monday. Significant mountain travel impacts expected. Thunderstorms possible Sunday afternoon and evening. Warm and dry weather returning Tuesday through next week.
Discussion
The initial upper trough has begun to move across Northern California this evening. Radar shows light reflectivity across much of the CWA, although low level dry air is hindering much precipitation making it to the ground. Main area for light QPF through the morning will be in Shasta County, and the foothills/mountains north of I-80, although some Valley showers in the northern portion of the forecast area cannot be ruled out.
Snow levels remain above 5500 feet through the overnight hours, increasing again with daytime warming. Primarily dry weather this afternoon although some additional isolated to scattered showers will be possible north of I-80. Onshore flow is bringing some gusts from 20-30 mph to interior NorCal this morning, with breezy winds expected to continue today.
Main trough axis approaches California late tonight with impacts from this weather system continuing through Monday. Precipitation will spread from north to south during the overnight hours, becoming widespread by Sunday morning and afternoon. The forecast appears to be on track for snow and rain amounts with only minor changes made in the overnight package.
The Winter Storm Warning continues for above 4500 feet beginning tonight and continuing through Monday morning. Minor snow accumulations will be possible down to 3500-4000 feet both Sunday and Monday mornings. The heaviest mountain snow and Valley precipitation are expected on Sunday. Along with the wet weather, gusty onshore are expected again tomorrow which may lead to reduced visibilities especially in the mountains with falling snow. Mountain travel delays and chain controls are expected Sunday.
Thunderstorms will be possible Sunday afternoon and evening across the CWA, although they will greatly depend on how much instability can be reached as cloudy skies are anticipated much of the day.
The best chances remain in the western portion of the Sacramento and northern San Joaquin valleys, although some foothill/mountain storms cannot be ruled out. Hodographs indicate favorable conditions for rotating storms if they do manifest, and funnel clouds or a brief tornado would be possible.
The other threats with any storm would be small accumulating hail, gusty winds, and periods of heavy rain. Keep an eye on the forecast as details about storm potential become more clear.
Precipitation becomes much more showery early Monday morning with lingering mountain travel impacts possible as light precipitation continues through the day. The trough finally moves east of the area Monday night with ridging building in on Tuesday. Cool weekend and Monday temperatures warm back up to near average by Tuesday afternoon.
Extended discussion (Wednesday through Saturday)
Warm and dry weather expected later next week as strong high pressure covers the region. Highs will warm to around 10-15 degrees above average by Thursday and Friday with mid 80s to lower 90s possible across the Central Valley.
Ensembles indicate slight weakening of the ridge next weekend as a series of short- waves pass to our north through the PacNW potentially leading to slight cooling.