January 8, 2020 – Some lingering showers over the northern mountains and northern Sierra Nevada today, otherwise dry with areas of valley fog. A little wetter weather system tonight into Thursday which could bring minor travel problems to the Sierra due to several inches of snow. Dry weather on Friday with another weather system brushing the region during the start of the weekend. Winter Weather Advisory from 10 PM this evening to 7 AM Thursday.
Discussion
Weak system brushed across the area last evening with radar still indicating a few lingering showers across the northern Sierra. Precipitation amounts have been light, mostly under a tenth of an inch while a few spots reported close to two tenths of an inch. The system wasn`t strong enough to disrupt the low-level inversion with IR difference imagery showing the entire Central Valley socked in with stratus. Only localized reports of visibility around 1/2 mile or less.
An active northwest flow aloft will allow for successive fast-moving wx systems. The next system tonight into early Thursday looks a little wetter with a stronger vort max, better dynamics. Including all ensemble members yields an average of around a quarter of an inch or less in the Valley and a little over a half inch of liquid at BLU. Tonight’s system will be more impactful with a broad 4 to 8 inches of snow accumulation forecast across the northern mountains and northern Sierra Nevada with locally higher amounts possible over the peaks. A winter weather advisory has been posted.
Dry weather returns Thursday night and continues into early Saturday when another fast moving system is forecast to drop down from the northwest bringing a quick shot of mostly light QPF to mainly the mountains (similar to last evening’s).
Extended Discussion (Sunday through Wednesday)
Ensemble guidance continues to favor a period of long wave troughing for much of the west which means cooler temperatures and perhaps several shots of rain for interior northern California. High temperature forecasts for Sunday-Wednesday call for temperatures to 0-15 degrees below normal, with the coldest areas being found over the mountains.
Sunday, we should see mostly dry conditions, with some showers being possible over the higher elevations of the Cascades and northern Sierra. Chances for precipitation then increase Sunday night into Monday as shortwave pivots around the broad trough. Guidance indicates this system will be bit more wet and have lower snow levels than the weekend storm.
Looking beyond Monday, NBM guidance keeps chances for precip over interior NorCal each day, which supports the ensemble views of cooler and wetter weather. Deterministic models suggest we could see a more potent and cold system mid-late week; however, confidence on timing and location for this system remains low. Kept NMB guidance in the forecast since the deterministic models are not on the same page as the ensembles just yet.