A fast-moving system brings widespread rain and mountain snow this afternoon through Wednesday with breezy southerly winds and hazardous mountain travel. Another system moves in over the weekend bringing another round of widespread precipitation, mountain snow and potential travel impacts.
Discussion
Latest GOES-West visible satellite imagery shows mostly cloudy skies being observed across much of interior northern California on this Tuesday afternoon. Current radar shows precipitation starting to spread inland from the southwest to the northeast, associated with the next weather system that will be impacting northern California over the next 24 hours or so. Current temperatures are trending approximately 3 to 15 degrees cooler than 24 hours ago, valid at 130 PM PST.
This current weather system will continue to move inland, and bring widespread precipitation and mountain snow to interior NorCal through Wednesday. Snow amounts have trended higher for this timeframe.
The Winter Weather Advisory has been upgraded to a Winter Storm Warning for northern Sierra Nevada, Lassen Park, and western Plumas County area above 4000 feet from 7 PM PST this evening through 10 PM PST Wednesday.
Heaviest snowfall is expected to be from around 9 PM PST this evening, through around 4 AM PST Wednesday where snow rates of 1-2 inches per hour will be possible. Snow levels start off around 5000-6000 feet today, and lower to around 3500 to 4000 feet overnight into Wednesday. Snow continues on Wednesday, but is not expected to be as heavy as the overnight hours. Snow showers continue tomorrow evening and then taper off overnight. The National Blend of Models (NBM) has a 70 to 80 percent probability for at least 18 inches of snow on Interstate 80, and a 70 to 80 percent probability for 12 inches of snow along Highway 50 through Wednesday afternoon.
Mountain travelers should plan ahead for travel delays, chain controls, snow covered roads, and reduced visibility at times, especially if traveling during this timeframe. Breezy to locally gusty southerly winds will develop today and continue through late tonight.
Wind gusts of 20 to 35 mph will be possible in the Valley and foothills, and up to 35 to 45 mph over the Sierra Nevada. As far as rainfall, the Valley can expect a half inch to an inch of rain through Wednesday evening.
The foothills can expect an inch to an inch and a half of rain over the same time period. Slick roads and longer than normal commutes will be possible. Heaviest rain is expected this afternoon through tonight. There is also a slight chance (10-15% probability) of isolated thunderstorms in the vicinity of the Delta this afternoon and evening.
Precipitation becomes more showery later on Wednesday and then tapers off Wednesday night. Dry conditions then return, and then a weak shortwave brings additional chances for light showers Thursday night into Friday morning, with best chances in the mountains and little to no impacts expected.
Cold morning low temperatures are forecast on Thursday and Friday mornings, in the 30s for much of the Valley where areas of frost and fog are possible.
Extended Discussion (Saturday through Tuesday)
Our second system will begin impacting our forecast area Saturday morning with the most impactful precipitation occurring through Saturday night. Showers will linger over the mountains into Sunday morning. Snow levels continue to be generally 3000-4000 feet on Saturday and lowering throughout the event.
Heaviest snowfall rates are projected to be Saturday morning and afternoon. With this system from I-80 through south of Hwy. 50, probabilities for 12 inches or more are 60-80% and 30-60% chance to see 18 inches or more.
The current path of the system looks to keep impacts for the Valley at a minimum with only 0.10-0.25″ expected through the Valley Saturday and Sunday. Probabilities show a 30-50% chance of seeing 0.25″ or greater in the Valley south of Red Bluff with a 50-80% chance across Redding and the Northern Sacramento Valley.
Additionally, south to west winds increase Saturday morning through Saturday evening as the system moves through the area.
Following the weather system, ridging will move back in and a drier pattern will prevail through the early parts of next week.
Gusty north to west winds develop late Sunday morning and continue into Monday afternoon with a warming trend Monday and Tuesday.