Stronger Pacific storm slated for Wednesday through Friday

January 23, 2018 – Fair today with some patchy morning valley fog and drizzle. Stronger Pacific storm impacts the area Wednesday into Friday with periods of moderate to heavy rain, mountain snow and gusty wind. Drier weather over the weekend.

Discussion

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Satellite imagery showing plenty of low clouds and patchy fog still lingering across much of the Central Valley, and in the mountain valleys, while the remainder of interior NorCal is seeing mainly clear skies other than some high clouds beginning to spread onshore ahead of the mid-week weather system. The depth of the stratus layer over the Sacramento region has decreased overnight as the subsidence inversion has strengthened, so probably little if any drizzle expected this morning.

Dry weather today, with milder temperatures for most areas, under upper level ridging.

Little change to current forecast other than to slightly slow down the onset of precipitation across interior NorCal on Wednesday. Still appears a more impactful system will affect the region mainly Wednesday and Thursday with a good shot of precipitation, heavy mountain snow with lowering snow levels, and gusty winds.

Heavy snow expected in the mountains of Western Plumas and Northern Sierra Nevada Wednesday night into Thursday and have a Winter Storm Watch in effect. Several feet of snow is possible over the highest elevations. As snow levels lower significantly behind the front Wednesday night and Thursday, accumulating snow in the Coastal and Shasta mountains may warrant additional winter weather products. Could also see some light accumulations in the upper elevations of the NE foothills and Motherlode Thursday.

Unsettled weather continues Thursday as post frontal upper troughing moves through. Models showing limited CAPE attm Thursday, but trending up. With steepening lapse rates Thursday afternoon as 5H temps cool into the lower -30s Deg C, will need to continue to monitor for potential thunderstorm activity. Storm total liquid QPF for this system ranges from about a 1/3″ to 1.5″ in the Central Valley (highest in the Northern Sacramento Valley) with 1 to 3 inches for the foothills and mountains.

Extended discussion (Saturday through Tuesday)

Jet stream and associated moisture will be draped across northern California Saturday as upper level heights rise with building ridge and push unsettled weather northward and out of the forecast area. The northern Sacramento Valley and northern mountains can expect chances for rain and light mountain snow accumulations Saturday and Saturday night. High pressure dominates Sunday and brings a return to dry conditions before the next weather disturbance moves inland for the beginning of the next workweek. High temperatures through the extended forecast period will be near to slightly above average for January.