Clear and dry conditions prevail this afternoon, chilly overnight temperatures through the week. Active weather pattern returns mid-week and through the weekend. Cold morning temperatures today through Tuesday with near to below freezing morning lows. First storm moves in Tuesday – Wednesday with moderate travel impacts from mountain & potential upper foothill snow. Second storm moves in Friday – Saturday with additional travel impacts in the mountains from snow.
Discussion
Drier weather prevails across interior NorCal this afternoon and is expected to continue as we enter the work week. Yesterday’s fast moving yet potent system brought some 1 foot or more snow totals to some of locations in the Sierra. The Sierra Snow Lab reported 13.6 inches of snowfall, the Sugar Bowl Ski Resort reported 18 inches at the summit, and Bear Valley Ski Resort reported 17 inches.
Some upper foothill snow totals came in this morning as well, Grass Valley had a report of 0.3 inches of snowfall this morning and a CoCoRaHs site near Camino reported 2.2 inches (elevation: 3038 feet). A report from Quincy (elevation:4195 feet) showed 4 inches of snowfall and a CoCoRaHs site (elevation:3168 feet) near Nevada County reporting 2.5 inches of snowfall. In Shasta County near Shingletown 3 inches of snow was recorded by a CoCoRaHs site.
Chain controls on I-80, SR-257, and SR-28 are still in place this afternoon (as of 1:30 pm), so make sure to check road conditions at quickmap.dot.ca.gov if hitting roadways this afternoon/evening.
Upper level ridging is beginning to fill in the area and cooler air begins to overtake the region. Northwesterly winds of 15-20mph are being reported at various METAR sites in the Valley this afternoon. Gusty winds are forecast to weaken this evening.
Clear skies and light northerly winds will allow overnight temperatures to fall near or below freezing for much of the Valley tomorrow morning. The NBM still has probabilities of around 40-100% for the Valley reaching 32 degrees Monday morning. Widespread frost is also likely tomorrow morning. Overall, dry conditions are expected on Monday then on Tuesday our next weather system begins to encroach on the area.
A shortwave trough is expected to move in from the northwest, which will setup extensive longwave troughing across the northwestern and central portions of the country. The current forecast track of the shortwave looks to be east of interior NorCal, similar to Saturday’s system, so rainfall impacts in the Valley look to be limited Tuesday and Wednesday. Current NBM probabilities of 0.25″ inches in the Valley are generally below 30%, except for Redding and areas northward with higher 40-80% chances for Tuesday and Wednesday.
Most of the impactful precipitation will once again be in the Sierra and north of Shasta Lake. Snowfall with this system looks to be similar to our previous system, although not as intense and spread out over the course of Tuesday and Wednesday, with the highest totals occurring Wednesday.
Snowfall accumulations of 6-15 inches are forecast for higher elevations in the Sierra from this system through Wednesday night. NBM probabilities are currently around 40-80% for 12 inches of snowfall or more and 30-60% for 18 inches of snowfall or more for areas including I-80, HWY. 50, and areas southward.
Snow levels are currently forecast to be 4,000 – 5,000 feet Tuesday, then lowering to 2,000 – 3,000 feet on Wednesday. Little to no snowfall accumulation is expected for elevations below 2,500 feet from this storm.
Gusty winds also pick up on Tuesday and Wednesday, with 25-45mph gusts possible at Pass levels and peaks. Variability still remains regarding track of the system, however confidence is increasing on this being another potentially impactful high elevation storm and as such a Winter Storm Watch has been issued for Western Plumas County/Lassen Park- West Slope Northern Sierra Nevada, including the cities of Chester, Quincy, and Blue Canyon. The current watch time begins at 4PM Tuesday Jan. 9th through 4AM Thursday Jan. 11th.
Stay tuned for forecast updates as we move through the week and possibly upgrade to a Winter Storm Warning.
Areas including Shasta Lake and Northern Shasta County, including areas of I-5 are also forecast to receive snow with this mid-week system. Current forecast totals for the aforementioned areas range from 6-12 inches, with locally higher amounts across the higher elevations.
Similar to locations in the Sierra, Wednesday looks to be when most of the heaviest snowfall will occur. NBM probabilities of 8 inches of snowfall or more along I-5 are currently 10-40%. Again, stay tuned for updates to the forecast as we begin the work week for adjustments to the forecast and possible issuance of any products.
Extended Discussion (Thursday through Sunday)
Ensemble guidance and cluster analysis indicate that an unsettled weather pattern is favored over much of the extended forecast period. The mid-week system looks to be well out of the area on Thursday, allowing for dry conditions to return.
Cold morning lows are in the forecast for Thursday, especially if skies clear. For the Valley, the National Blend of Models (NBM) has generally a 65 to 95 percent probability of 32 degrees or less for the morning low on Thursday, and a 45 to 85 percent probability for 28 degrees or less mainly north of Sacramento.
The next weather system is expected to move in Friday into Saturday. The main impacts with this system would be mountain snow, with potential travel impacts, and minor accumulations into the upper foothills.
Showers and light rain may bring slick roads at times as well to the lower elevations. Lingering showers will be possible across the area on Sunday as well.
There is still uncertainty with this system though, so be sure to stay tuned for more details as we get closer!