March 14, 2020 – Cold weather system will bring widespread rain and mountain snow this weekend into next week with mountain travel impacts and low snow levels. Below average temperatures continue through next week.
A strong, cool upper low will bring heavy mountain snow this weekend into early next week, as well as widespread rain in the Valley and foothills. Mountain snow developed overnight, heaviest from around Highway 50 southward. Chains controls are currently in effect for Highway 50, Highway 88, Highway 4. I-80 has seen snow showers since around midnight east of Blue Canyon, with accumulations from around Kingvale eastward. Scattered showers have also developed over the northern Coastal Range and Shasta County. Heavier snow showers are expected behind a cold front, which will exit the area later this morning. Snowfall amounts could exceed an inch or more an hour over the northern Sierra later this afternoon. Heavies snow is expected tonight into early Sunday evening. A Winter Storm Warning remains in effect from 5 am this morning to 5 pm Monday. Storm total snow amounts from ensembles project 3 to 6 feet over the northern Sierra to Lassen Park area, around a foot for the Coastal Range. When combined with winds gusting to around 60 mph, whiteout conditions are possible.
Sierra snow levels are currently around 5000 feet and are expected to drop to 2500-3500 feet by Monday morning. As for the Coastal Range, Shasta County mountains, and southern Cascades, snow levels will start out at 2500-3000 feet this morning, then drop to 1500-2500 feet by Monday morning.
For the Valley, the NAM 3km, NMM and HRRR suggest the Sacramento metro area southward will some rain showers later this morning, while the western side of the Valley to the north could see quite a bit of shadowing, limiting precipitation there to some extent until later this evening and tonight, when precipitation will become more widespread. Preliminary QPF amounts indicate 0.50-1.25 inches of rain in the Valley, and 2-6 inches (locally higher in thunderstorms) of liquid precipitation over the mountains today through Monday.
Breezy southerly winds are expected today, but have most likely already peaked in intensity this morning. Strongest gusts in the Valley have been over the northern Sacramento Valley at around 30 mph.
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In addition to widespread precipitation, thunderstorm development could be possible Sunday afternoon as instability develops. Small accumulating hail is possible with any thunderstorms that form. Thunderstorms have also been added Monday afternoon to the far eastern side of the Valley into the foothills.
With the upper system over the West, temperatures will remain 5 to 15 degrees cooler than normal over the weekend. Valley highs will cool into the mid 50s, while mountain locations will observe highs in the upper 20s to low 40s.
Extended discussion (Wednesday through Saturday)
Double barreled closed upper lows over CA continues to rotate around each other in a Fujiwhari effect during the middle of next week. Significant differences in related QPF during this period between deterministic models leads to a lowered confidence forecast at that time. Lows weaken and progress east Thursday as next upstream closed upper low approaches Friday into Saturday. This will lead to more unsettled weather into next weekend.