March 18, 2020 – Cool and unsettled weather will continue much of the week. Another strong winter storm will be possible early next week.
Discussion
Large trough continues to evolve along the West Coast with multiple low centers moving about. NorCal is presently between a closed low over northwest Nevada and a vort dropping quickly southward off the coast. Radar shows scattered, mainly light, showers continuing across the region mainly to the north of I-80. Current temperatures range from the 20s and 30s in the mountains to the upper 30s to mid 40s across the Central Valley.
Cool, showery weather will continue the next 24 hours as the NW Nevada low wobbles back into NorCal. QPF will be generally light, and mainly over the mountains. The winter weather advisories have been trimmed back to just the extreme southern Cascade Range, though it’s possible some accumulating snow will develop further south into the northern Sierra during the day and into this evening.
Gradually milder, and less unsettled weather is expected for the second half of the week. Precip chances will taper with any additional QPF forecast to be light and mainly confined to the mountains.
Extended discussion (Sunday through Wednesday)
Lowered confidence in forecast over the latter part of the weekend as model differences exist with handling of closed upper low off the CA coast. Models however start to come into better agreement early next week as another large low pressure system drops slowly down the PacNW coast Monday into Tuesday. Widespread precipitation is expected over interior NorCal during this period with significant mountain snow possible. ECMWF opens low to trough and swings it inland Tuesday night into Wednesday, while GFS-20 keeps digging the low off the CA Coast. This solution looks better given recent lows and their track. GEFS/GEPS support a similar solution, but weaken low to trough as it digs offshore. Therefore, expecting widespread precip threat to continue Wednesday as snow levels lower into the foothills.