Light rain and snow showers continue through the afternoon. Moderate to heavy snow is forecast over the mountains tonight and Wednesday with a second weather system. A dusting of snow is possible in the northern Sacramento Valley overnight. Snowfall accumulations are also expected in the foothills. Cold but drier weather is expected later in the week.
Discussion
Long wave troughing continues over the North Central US with a few shortwaves making their way down the west coast and across interior NorCal. The first of these waves is moving across the area this afternoon and is the weaker of the two systems. Light rain and snow showers have been seen across much of the area today with some flurries reported earlier this morning in a few Valley locations including Redding and Red Bluff.
QPF from this system remains light but will pick up later tonight as the second, wetter, shortwave moves through. Expect heavier precipitation to pick up later this evening with light to moderate rainfall in the Valley and moderate to heavy snow over the mountains and into the foothills.
Snow levels remain lowest over the northern portion of the Sacramento Valley and surrounding terrain, roughly 500 to 1500. Overnight into tomorrow morning, the far northern and western portion of the Valley and lower foothills, snow levels may be as low as a few hundred feet and even to the Valley floor for a brief period. Probabilities for snow at RDD have decreased with about a 30 percent chance for a dusting according to the NBM, lower to 0 percent chances further south into the Valley.
Will continue with the Winter Weather Advisory due to the potential for any snow in the northern Sac Valley. Over the eastern foothills from Butte County northward, snow levels are generally around 1500 feet, locally down to 1000.
Further south in the foothills of the Sierra Nevada, including the Motherlode, snow levels are a bit higher around 2000 feet, although some light snow could be possible around 1500. With significant foothill snow forecast, have continued the Winter Storm Warning for these locations into the mountains of the Sierra Nevada, Cascades, and northeastern Shasta County.
At pass levels in the Sierra Nevada and Cascades, a half to one foot of additional snow is forecast. Slightly higher amounts south of Highway 50. Precipitation will begin to become lighter tomorrow afternoon, with some lingering mountain showers and Valley rain showers through the evening hours.
May be some clearing in the northern Sacramento Valley late Wednesday night which would bring in cold overnight lows to the area, with Valley lows in the mid to upper 20s.
Elsewhere, clouds will limit lows to the mid 30s to low 40s. Clouds return Thursday as another system passes to the east. A mountain shower could occur but not a lot of QPF is predicted at this time. Ridging and cold temperatures return behind this exiting system.
Extended Discussion (Saturday through Tuesday)
Dry conditions and below normal highs are expected for the first day of 2022 given high pressure ridging. Unusually cold minimum temperatures are still being depicted by the ECMWF EFI this weekend, especially over the northern Sacramento Valley.
Overnight minimum temperatures in the Valley will be in the mid 20s to low 30s with teens and single digits expected over the mountains. Anyone planning outdoor recreation in the mountains should be prepared for very cold conditions.
While ensemble cluster analysis continues to show some differences regarding timing and placement of the trough, there is increasing confidence in the potential for another winter storm event for early in the year. NBM probabilistic guidance shows at least a 50-75% chance of exceeding 12″ of snow across the northern Sierra and southern Cascades through Tuesday afternoon (64% chance of at least 12″ of snow at Donner Pass). Mountain travel disruptions are likely with the potential for chain controls and travel delays. Periods of gusty winds are also possible.