Active weather will bring rain, mountain snow, and breezy to gusty southerly winds today into the weekend. Drier weather anticipated early next week.
Discussion
Mostly cloudy skies and gusty winds are being observed across interior Northern California with current temperatures in the 40s-50s in the Valley/foothills and 20s-30s in the mountains. Scattered showers are bringing light rain to portions of the northern Sacramento Valley early this morning as the first shortwave in a series of weather systems moves through NorCal.
The moisture with this first wave will be focused further northward, with the majority of accumulating precipitation expected north of I-80. Current probabilities of exceeding 0.5 inches of rain sit around 70% to 95% across the northern Sacramento Valley and surrounding terrain and along the Sierra/southern Cascades from I-80 northward, falling to 20% to 40% probabilities south of Interstate 80. Current ensemble trends indicate a 3-6 hour break between systems.
This evening with the next shortwave progressing through interior NorCal overnight tonight into Friday. The associated moisture plume is projected to take a slightly further southward trajectory, resulting in a better opportunity for more widespread precipitation on Friday. Resultant probabilities of rain exceeding 0.5 inches increases to 30% to 60% across the Delta, southern/central Sacramento Valley, and northern San Joaquin Valley, with 60% to 80% probabilities of exceeding 1 inch across the northern Sacramento Valley and surrounding terrain and along the Sierra/southern Cascades.
Today, snow levels will be 5000 to 6000 feet, before rising to 7000-8000 in Friday. Current probabilities of snowfall exceeding 6 inches through midday Friday sit around 40% to 70% above 6000 feet at this time. As a result, a Winter Weather Advisory remains in effect until noon on Friday, with mountain travel impacts anticipated. Additionally, southerly winds are expected to gust 20 to 40 mph with the strongest winds from Yuba City to Red Bluff.
The active weather period then continues across interior NorCal into the weekend underneath broad northwesterly flow aloft. This flow pattern will allow another shortwave ejection, similar to today’s system, into the region. As a result, the majority of precipitation on Saturday is expected from Interstate 80 northward at this time. Attendant probabilities of exceeding 0.5 inches of liquid precipitation around 60% to 80% favor the northern Sacramento Valley and surrounding terrain and the Sierra/southern Cascades north of I-80, with probabilities generally less than 20%. elsewhere. Given high expected snow levels above 8000 feet, only light accumulations at peaks are expected on Saturday.
On Sunday, ensemble PWAT anomaly shows another push of moisture reinvigorating Saturday’s system bringing yet more rain and colder air. Snow levels will initially sit around 6000-7000 feet before lowering that afternoon to 5000 to 6000 feet Sunday afternoon. Currently there is a 20 to 40% chance of snow accumulations exceeding 4.00 inches.
Highest rainfall accumulations will once again be over Shasta County and the foothills/mountains with a 50 to 90% chance of 0.5″ or more on Sunday. Lower probabilities over the Valley with a 30 to 50% chance of 0.5″ or more of rainfall north of I-80. Sunday will also bring a 10 to 20% chance of isolated thunderstorms over the Valley and Sierra Nevada foothills/mountains.
Please continue to check weather.gov/sto for the latest updates and check quickmap.dot.ca.gov before you travel!
Extended Discussion (Monday through Thursday)
Models showing interior NorCal will be under the influence of upper level ridging through the extended forecast period. High temperatures will be near to slightly above normal with chilly nights. Potential for some patchy overnight fog or frost in the Central Valley. NBM showing potential for some precip over northern portions of the CWA Wednesday into Thursday, however confidence in this is low given progged synoptic pattern.