A brief period of dry weather is expected through this morning before some valley rain and mountain snow returns. Another more potent weather system will bring heavy precipitation and strong winds late Friday through Sunday creating major mountain travel impacts.
Discussion
Active weather is expected through the weekend with multiple weather systems moving through the region. Clouds have already begun to fill in across the northern Sacramento Valley in response to an approaching upper-level trough.
This will keep things a bit warmer this morning and should limit fog potential to mainly the Northern San Joaquin Valley and portions of the Southern Sacramento Valley this morning, where dense fog has already spread from Modesto to Stockton. Based on latest hires guidance and cloud cover trends, decided to issue a Dense Fog Advisory til 10am this morning for this region.
The upper-level trough and cold front will push into the region as early as late morning today, first reaching Northern Shasta County and the Coastal Range.
This system will bring shower chances to the area starting this afternoon in the northern part of the area with showers continuing and spreading south during the evening and overnight. The better forcing will still be over northern areas and which is where we can expect the highest QPF with this system.
Snow levels will be lower in the 2500 to 4000 foot range with most of the accumulation above 3500 feet. Generally looking at 6-12″ from about I-80 north with some locally higher amounts on the higher peaks.
Flow will become more zonal on Friday and we should see a break in precip mid-morning into the afternoon.
Then a deeper trough will dig into the region, which will bring more impactful weather for the weekend with widespread rain, heavy mountain snow, and strong winds.
Warm air advection precip will develop during the evening and overnight ahead of the approaching trough. Precipitation will become heavier on Saturday as the cold front slowly pushes south.
Snow levels will be starting out 3000-4000 feet and will rise up to 4000-5500 feet Saturday before falling back down to 2500-3500 feet Sunday.
Low-level winds will amp up substantially ahead of the approaching trough on Saturday with a strong low-level 850-700 mb jet bringing winds of 50-70+ knots. This will bring strong southerly winds starting overnight Friday with the strongest winds Saturday morning through Saturday night. Widespread gusts 35-45 mph can be expected in the Valley with some localized gusts around 50 mph across the Northern Sacramento Valley, and 45-60 mph in the mountains.
These strong winds along with heavy snow will bring whiteout conditions and near impossible travel on Saturday over the mountains.
Cold front will be south of the area on Sunday with the trough axis slowly pushing east through the region. This will keep showers in the forecast for lower elevations and widespread snow over the Sierra.
Snow levels will be lowering on Sunday falling to 2500-3500 feet. Some weak instability may build in on Sunday and that will bring an isolated chance for thunderstorms.
Extended Discussion (Monday through Thursday)
A few showers will linger mainly into early Monday but they will be low impact. A potentially brief, upper-level ridge then builds in bringing quiet weather on Tuesday.
Cluster Analysis and the latest ensembles are advertising another trough may impact the region sometime mid to late week, but the timing, strength, and impacts with this system are still unclear.