Cool and unsettled weather with showers, mountain snow, breezy winds, and isolated thunderstorm chances for the first part of this week followed by dry and seasonably warm temperatures late-week into the weekend.
Discussion
Current GOES-West infrared satellite imagery shows the passage of some mid to high level clouds over portions of interior northern California early this morning. Temperatures are generally in the 50s in the Valley, 40s in the foothills and 30s in the mountains as of 0200 PDT this Monday morning.
A quick-hitting weather system will approach the area today, bringing along the return of cooler and unsettled weather through mid-week. Showers and mountain snow are forecast for Monday afternoon into Tuesday, with lingering mountain showers into Wednesday. Current storm total snow amounts are generally 4 to 10 inches from this afternoon through Wednesday, with the heavier amounts falling mainly above 4500 feet. Locally higher amounts will be possible over higher elevations such as at Lassen National Park.
A Winter Weather Advisory remains in effect for Lassen/western Plumas and the west slope northern Sierra Nevada from 5 PM this evening through 10 AM Tuesday morning.
Breezy to locally gusty southwest winds will accompany this system this afternoon into Tuesday, with the strongest over the mountains where gusts of 35 to 45 mph will be possible.
Snow levels will start off around 4000 – 5000 feet Monday and will lower to around 2000 – 3500 feet Tuesday. Up to a few hundredths of an inch of rain are expected in portions of the Valley, with up to a few tenths of an inch in the foothills, mainly late Monday into early Tuesday. Periods of slick roads will be possible.
In addition, this weather system will bring along chances for isolated thunderstorms this afternoon and evening. The best chances are in the northern Sacramento Valley and surrounding terrain, where the National Blend of Models (NBM) offers probabilities of 15 – 26 percent probability of thunderstorm development during that timeframe. Lightning, gusty winds, heavy rain and small accumulating hail will be possible with any thunderstorms that develop. Dry and warmer weather builds back in for Thursday.
Extended Discussion (Friday through Monday)
Ensemble guidance and cluster analysis indicate upper level ridging to build into the region late week and into the weekend, suggesting dry weather and a warming trend through Saturday. Models slightly diverge late weekend into early next week, but at this point a slight cooling trend looks better for Sunday and Monday as the the upper level ridge looks to flatten. Either way, temperatures are trending warmer for the extended forecast period compared to the next few days, with above normal temperatures for Saturday.