Dry weather returns today, with chilly lows this morning and again Friday morning. Another storm system spreads in Friday afternoon and continues into early Sunday with periods of heavy mountain snow and mountain travel impacts.
Discussion
Dry weather returns today as the storm system exits to the southeast with dry northwest flow and upper level ridging. Temperatures this morning will be cold, with Valley lows near freezing. North winds around 5-12 mph should keep temperatures from getting colder, with coldest temperatures in wind sheltered locations.
Skies will be mostly sunny over the Valley and Delta, with some clouds lingering over the mountains into the afternoon. Friday morning again is expected to have Valley lows near freezing. Winds will be lighter, but increased cloud cover ahead of the next system should limit radiational cooling to some extent.
The next storm begins to spread in Friday morning over Shasta County and then spreads southward throughout the afternoon and evening. Snow levels with entrenched cold air over Shasta County will be fairly low at 1500-2500 feet Friday, then rising to 3000-4000 feet Saturday, then 4500-5500 feet Saturday night. Expect snow accumulations in that area above 3000 feet around 6 to 12 inches, locally higher over peaks, and with 1 to 3 inches along I-5. A Winter Weather Advisory may be needed.
Heavy snow is projected over the northern Sierra and the southern Cascades from Friday afternoon into early Sunday, with 6-18″ possible along the Sierra above 4500 feet, and up to 2 feet at higher peaks. Probabilities of greater than 12 inches snowfall from Friday afternoon through Sunday morning across the I-80 and Hwy 50 corridors have grown and are now 60-90%.
This system will be different from the last one with in having higher snow levels, starting around 3500 feet Friday, then rising to 4000-5000 feet Saturday morning, then 5000-6000 feet Saturday night.
Confidence continues to grow that we will see travel impacts from periods of heavy snow and reduced visibility, with winds along higher elevations 40 to 50 mph over the Sierra crest. As a result, we have issued a Winter Storm Watch for Western Plumas/Lassen Park and the West Slope of the Northern Sierra Nevada areas from 4 pm Friday through 4 am Sunday for heavy snow and winds gusting as high as 50 mph.
Travel may be very difficult with delays, likely chain controls, reduced visibility with snow covered roads and possible road closures. Snow showers are expected to taper off through Sunday morning. Anyone planning on traveling into the mountains over the weekend is urged to monitor the forecast and adjust their schedule accordingly.
Rain impacts will be more significant with the weekend system with moderate rain at times, with totals of 0.33″-1.25″ of rainfall in the Valley expected, 1.25″-2.50″ in the foothills. Local ponding on roads and low lying areas is possible at times.
Extended Discussion (Monday through Thursday)
Dry weather expected Monday into Tuesday as strong upper levelridge in EPAC builds inland. Some morning valley fog will be possible and forecast high temperatures expected near normal.
Model solutions diverge Wednesday leading to some forecast uncertainty. NBM/EC bring another round of precip into the CWA Wednesday/Wednesday night, while GFS maintains upper ridging through midweek. Ensembles/clusters lean toward drier upper ridging solution.