Dry weather through Monday with chilly nights and above normal high temperatures. Colder unsettled weather expected Tuesday into Saturday. Continued unsettled weather next weekend with more rain/snow opportunities, break on Saturday.
Discussion
EPAC upper ridging continues to build inland today with warming air mass. High temperatures expected in the mid to upper 60s this afternoon in the Central Valley with 40s to lower 60s in the foothills and mountains.
Increasing northerly flow aloft, along with tightening N-S surface pressure gradient, will result in some gusty north to east wind today, lingering in portions of the northern and eastern foothills/mountains into early Monday.
Additional warming Monday with highs in the upper 60s to lower 70s in the Central Valley, max temps warmest in the Northern Sacramento Valley. EPAC high retrogrades Tuesday as cold deep troughing sets up along the West Coast.
Models showing shower possibilities beginning Tuesday afternoon and continuing Tuesday night. Best chances over the mountains, mainly northern and eastern portions, with highest QPF over the Sierra Nevada.
Much colder air begins to be ushered in Tuesday with highs 5 to 15 degrees lower than Monday. Snow levels begin around 4000 to 5000 feet Tuesday afternoon, lowering into the foothills Tuesday night.
Wind increases Tuesday with advisory speeds possible in portions of the Central Valley.
Cold deep troughing modeled over interior NorCal Wednesday. Snow levels Wednesday morning could be down to around 500 feet, however available moisture will be limited with main shower chances over the foothills and mountains.
Snow levels increase above 1000 feet by Wednesday afternoon. Snow ratios will be large due to cold nature and potential for significant snow amounts over higher elevations of the Sierra Nevada.
Low 50s forecast for highs in the Central Valley Wednesday with 20s to 40s in the mountains and foothills.
Extended Discussion (Thursday through Sunday)
Ensembles continue to show a second cold trough from western Canada pushing southward along the coast Thursday into Friday. This system will bring another surge of cold air. 850 mb temperatures early Thursday are projected to be around -9 C over the northern Sacramento Valley, with morning lows around freezing to just below. The Valley will be fairly shadowed, though, so there should be limited precipitation there, generally a few hundredths of an inch.
There is a slight chance of a mix of rain and snow flakes could be seen early Thursday and again early Friday, most likely with no accumulation. The potential for impactful snow is over the mountains and foothills.
Foothill towns such as Paradise, Grass Valley, and Sonora could potentially see several inches of additional snow with the second system. There remains a large range of uncertainty over exact amounts at this point, though.
Snow levels are also low enough that light accumulations are possible into some lower foothills towns, which could bring travel impacts.
The mountains are forecast to see another foot or so of snow, though this will be high ratio (~17:1) fluffy snow, with liquid equivalency around generally less than an inch.
The period with the highest impact to mountain travel is Thursday afternoon and evening, with the best upslope flow and amounts now being projected for the I-80 corridor. Some additional snow is possible through the day Friday.
Shower activity winds down Friday evening, with dry weather returning Saturday.