A few light showers will be possible over the mountains today as a weather system moves through. Cool and dry weather Tuesday and Wednesday with near freezing minimum temperatures in the Central Valley. Widespread precipitation returns Wednesday night through the weekend.
Discussion
Quick hitting, mainly dry, system is moving south into NorCal early this morning. Satellite shows mid and high clouds spreading into the region as a cold front enters far northern California, and radar is indicating a few showers already across northwest California. Further to the south, some light fog has begun to form over the northern San Joaquin Valley. System will brush by the area today bringing cooler temperatures and a few light showers over the mountains.
Some areas of fog will be possible early this morning in the Central Valley as winds diminish and RH nears saturation.
Dry weather expected Tuesday into midday Wednesday ahead of the next system. This will set the stage for a couple of cold mornings with near freezing temperatures likely across the valley and areas of frost. Lows are expected to be in the upper 20s to mid 30s.
Pretty consistent ensemble multi-run trends for QPF lend confidence that a more impactful system will begin to move into the region Wednesday afternoon and night bringing significant precipitation along with gusty winds.
Travel impacts from accumulating snow may begin as early as Wednesday evening across the northern mountains, but will likely hold off until late Wednesday night and early Thursday morning over the northern Sierra. If these trends hold, we’ll likely be issuing Winter Storm Watches for the NorCal mountains for late-week sometime during the next 24 hours.
Clusters are in overall good agreement with position of the trough on Thursday, and weak to moderate atmospheric river indicated via GEFS IVT supports continuing precipitation across the region with heavy snow in the mountains. Snow levels lower to around 2500-3500 ft in the northern mountains, and to 4000-5000 ft across the northern Sierra. 1-2 ft of snowfall accumulation will be possible over the higher elevations by sunrise Friday.
Extended Discussion (Friday through Monday)
A period of cold and unsettled weather is likely across the region late this week through the weekend. First system will be winding down Friday with lingering showers continuing to provide lighter snowfall accumulations over the mountains.
A second system will affect the region Saturday and Sunday bringing a second round of precipitation to NorCal. Clusters indicate greater uncertainty in the timing and location of this second trough, so confidence is not quite as high as the Wed-Fri system. GEFS also indicates a weaker IVT plume with the second system. Nevertheless, impactful snow will be possible over the mountains for the second half of the weekend.
Behind that, drier weather returns early next week with potential for more near-freezing temperatures in the valley Monday and Tuesday mornings.