Cold weather system moves into NorCal this morning with widespread light rain in the Valley, heavy mountain snow, and hazardous travel impacts. Conditions dry out Sunday and Monday, then unsettled weather pattern returns mid-week.
Discussion
Today’s incoming weather system makes it way into our forecast area in the next few hours with light snowfall beginning in Shasta County and then making its way down the Sierra through the morning. Hazardous travel conditions are expected as heavy mountain snow develops late this morning and continues through the afternoon.
Snow levels with this system are 2500 to 3500 feet this morning, lowering to 1000 Saturday night. Total snow accumulations of around 1 to 2 feet are forecasted with gusty mountains winds up to 55 MPH throughout the event.
Current probabilities for heaviest snow rates are in the afternoon time frame, south of Hwy. 49 including I-80 and Hwy. 50. There is a 50-90% of rates up to 2 inches per hour from noon to 4 PM with highest chances along I-80 and north of Hwy. 50. Snow accumulation probabilities along the Sierra exhibit a 50-90% chance of amounts above 12 inches with a 30-65% chance of amounts greater than 18 inches.
As a result, a Winter Storm Warning is in effect for for Western Plumas County/Lassen Park and West Slope Northern Sierra Nevada Counties including Interstate 80 over Donner Pass, Highway 50 over Echo Summit and Highway 88 over Carson Pass from 4 AM this morning through 4 AM PST Sunday.
The combination of heavy snow with gusty winds will make travel difficult to impossible with travel delays, chain controls, snow covered roads, and near white out conditions at times. If you must travel, have an extra flashlight, food, and water in your vehicle in case of an emergency.
Snow should start to taper off early tonight, with possible lingering snow showers lasting through midnight.
Additionally, a Winter Weather Advisory has been issued for the Shasta Lake Area and Northern Shasta County from 4 AM this morning through 10 PM tonight for snow accumulation of 2 to 8 inches in elevations above 2,500 feet. Travel could be very difficult and plan slippery and snow covered road conditions. Probabilities in Shasta Lake Area and Northern Shasta County are 20-75% for amounts greater than 6 inches, increasing as you move northward throughout the forecast area.
Rainfall will be a minimal impact aspect of the forecast given the quick moving nature of the weather system and how cold it is. Rain will begin in the Northern Sacramento Valley and have the front move down the Valley throughout the afternoon. Rain accumulations are forecasted 0.10-0.25″ in the Valley with up to an half an inch along the western portions of the Valley. There is a 30-70% chance of 0.25″ or greater in the Valley from this morning through tonight. The 00Z run of the HRRR does show a gap in rain accumulation between Red Bluff and Sacramento with only a few hundredths forecasted.
Conditions begin to taper off Saturday night with most measurable precipitation finished by midnight tonight, although travel impacts could extend into Sunday morning.
Upper-level ridging behind the weather system will help bring in drier and quieter conditions for Sunday and Monday. As things clear out, cold air moving in will bring in cold morning lows with frost possible Sunday and Monday morning. Valley early morning temps will be in the upper 20s to low 30s with NBM probabilities showing a 50-90% chance of temperatures less than 32 degrees Sunday morning across the Central and Southern Sacramento Valleys.
Unsettled weather returns on Tuesday with precipitation spreading in from the northwest, primarily over the Northern Sacramento Valley and mountainous areas.
Extended Discussion (Wednesday through Saturday)
Clusters continue to show unsettled weather midweek into the early weekend as several weather systems moving over Northern CA is possible. These systems keep colder air over the mountains and will allow for several rounds of snowfall accumulations. EC Meteograms show active snowfall accumulation during this time period but no periods of significant snow rates at this time at Blue Canyon.
Additionally, Sacramento meteograms show a similar pattern of active precipitation but remaining on the light side with 24-hr periods staying under a quarter of an inch. Afternoon highs look to be in the low 50s and upper 40s in the Valley with low 40s and 30s in the foothills and mountains.
There is still a great deal of uncertainty with the forecast so please remain tuned into further updates to the forecast.