Periods of light to moderate snow, rain, and breezy winds expected today through Friday with moderate mountain travel impacts. Northern CA remains in an active weather pattern at the end of this week into early next week.
Discussion
Satellite and observations show increasing clouds over the Valley ahead of the weather system impacting Northern CA later today. Precipitation makes its way over the Coastal Range this morning, spreading down the Sierra and into the Central Valley. This will be the first of several periods of precipitation through Friday night, heaviest this morning as the cold front sweep through the Northern Sacramento Valley and the mountains. Gusty winds also accompany today with gusts over the northeastern foothills 20-35 MPH, strongest this early afternoon before tapering off this evening.
Rain probabilities of an inch or greater for the mountains and Northern Sacramento Valley is 65-95% chance with a 30-60% chance for an half inch or greater for the Northern San Joaquin and Southern Sacramento Valleys. Overall, the Valley south of Red Bluff will see lesser rain totals with the heaviest amounts over the mountains and Northern San Joaquin as rain gets shadowed by the mountains.
Between now and Friday night, the Valley will see around 0.10-0.50″ with 0.50-1.50″, up to 2.25″ over the mountains/Northern Sac. Valley including Redding. Additionally, this system will bring isolated thunder chances today north of HWy. 32 and Thursday north of I-80 (10-20% chance). This does cross the Park Fire Burn Scar bringing the threat of debris flow concerns which will be closely monitored as convection develops throughout the day.
Periods of light to moderate mountain snow will also accompany this weather system, beginning early this afternoon through Friday night. Snow levels will be 5500-6500 feet when snow initially starts, dropping to 4500-5500 feet Thursday night, and 4000-5000 feet Friday morning.
A Winter Weather Advisory has been issued for the Western Slope Northern Sierra/Western Plumas/Lassen Park Counties above 5500 feet for snow accumulations of 6 to 12 inches and gusts up to 45 MPH from 10 AM Today to 10 PM Friday. Snow will be heaviest this late morning to early afternoon with another heavier periods Thursday night into Friday morning. NBM probabilities for amounts greater than 12 inches is 60-80% between today and Friday night, peaking south of Interstate 80. The peaks of Lassen National Park area may see to 2-3 feet of snow, with 12-18 inches across the higher peak of the Sierra.
Conditions begin to taper off on Friday outside of lingering snow showers across the Sierra through the evening hours. Northern CA remains in active pattern after another brief lull in weather on Saturday with more rain and mountain snow incoming Sunday into early next week. Afternoon high swill be relatively unchanged during this stretch, coolest Friday into Saturday morning.
Extended Discussion (Sunday through Wednesday)
Upper ridging moves through interior NorCal early Sunday followed by another short wave trough Sunday night into Monday. Widespread showers and mountain snow showers expected. Snow levels are forecast to be around 5000 to 6000 feet initially, lowering to 3500 to 5500 feet Monday morning. WPC advertising snow amounts up to around 7 inches, locally higher amounts over highest elevations. Liquid totals range from a few hundredths in the N San Joaquin Valley increasing to around 2 tenths in the N Sac Valley. In the foothills and mountains, QPF ranges from a tenth to around an inch.
Drier weather expected Monday night into midweek with some locally gusty north to east wind as upper ridging builds inland. Temperatures trend up through the extended forecast period, returning to near normal Wednesday.