January 21, 2020 – Weather system brings light to moderate amounts of precipitation to interior NorCal through tonight. Dry conditions return for the end of the week, then another weather system is possible by late in the weekend.
Radar and satellite imagery indicate the frontal zone is nearing the northwest corner of the state while some light pre-frontal precipitation is spreading inland across the far northern portions of the state. Otherwise, skies are mostly cloudy across the region early this morning with rather mild temperatures. Current readings range from the 30s in the mountains to the 40s across the Central Valley.
Front will continue to weaken as it shifts inland across NorCal today as stronger upper support with the trough lifts north of the area into the PacNW. Precipitation will gradually spread southeast through the day with some light rain likely in the Sacramento region as early as late-morning, but especially during the afternoon. Southerly breezes will also pick up during the day with gusts of 20-30 mph possible in the Sacramento Valley.
Snow levels will be moderately high, generally around 4500-5500 feet. A few inches of snowfall accumulation will be possible across the higher northern Sierra passes from mid-afternoon into the overnight hours tonight and could lead to some travel impacts.
Precipitation chances retreat to the far northern portion of the state during the second half of the week as ridging from the eastern Pacific moves in. Even weaker systems riding over the ridge will bring occasional cloudiness, but showers will mainly remain up by the OR/CA border. Generally milder temperatures expected, but areas of night and morning valley fog will likely become more prevalent.
Extended Discussion (Saturday through Tuesday)
While guidance continues to struggle with the timing and magnitude of the approaching shortwave, there is agreement upon the return of wet weather late Saturday into Sunday. Latest NBM guidance indicates precipitation gradually spreading southeastward during the day Saturday. Light to moderate snowfall accumulations might be possible at pass levels on Sunday. Latest ECMWF ensemble is indicating moderate probabilities of snow exceeding 12 inches over the Sierra and Lassen National Park. If you have mountain travel plans, stay tuned to the latest forecast. Lingering showers are possible into Monday, followed by dry conditions as an upstream ridge moves in.