Another strong winter storm will bring multiple feet of snow with major impacts expected once again over the foothills and mountains into early next week. Showery pattern will continue into the end of the week with several more inches of mountain snow possible. A warmer weather system is possible late week and into next weekend, but confidence is low on details and impacts.
Discussion
Main precip band is pushing through the Valley early this morning and will reach the Sierra and major highways by 3am with a period of very heavy snow and near zero vis with 2-4 inch snowfall rates possible. Near impossible mountain travel can be expected from 3am-11am. Snow is likely to taper off to snow showers overnight.
Somewhat unstable airmass will promote scattered showers and isolated thunderstorms to develop this afternoon, small hail will be the main impact. A persistent, nearly stationary upper level low will remain just offshore the Oregon/Washington coast through Tuesday.
Multiple lobes of vorticity will pivot underneath the main low center with the strongest today as the westerly Pacific jet over northern California reaches 150+ kts. This has led to a favorable overlap of height falls, PVA, and left exit diffluence to provide a large area of synoptic support for widespread precipitation over central and northern CA.
Snow levels generally remain below 2000ft through Tuesday. Additional snow probabilities are high for 8-12″+ over the Sierra Nevada with localized amounts of two feet likely in the High Sierra through through early Sunday.
A reinforcing trough rounding the offshore low will focus instability and orographics favoring a shower pattern with some dry periods Monday through Wednesday with high probabilities for >6″ over the Sierra Nevada above 5000 feet.
A few thunderstorms still look possible for Monday afternoon. Precipitation amounts for Monday and Tuesday generally look to be under a quarter inch for the valley and range from one quarter to around three quarters of an inch for the foothills and a third of an inch to around an inch for the mountains.
Extended Discussion (Thursday through Sunday)
Clusters keep trough over the area Thursday then transition to a flat ridge by Friday. Models are good agreement through next Wednesday with a relatively weak but cold system moving through the area that would continue low elevation snow for the foothills.
After Thursday the models differ greatly giving a wide range of uncertainty. GFS is building a ridge while the European favors more storms Friday and next weekend.