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January 24, 2018 – Strong Pacific storm impacts the area later today thru Friday with periods of moderate to heavy rain, mountain snow and gusty wind. Drier weather over the weekend.

Discussion

Offshore frontal system slowly approaching NW California as upstream trough continues to deepen over the eastern Pacific. Radar shows precipitation has begun over the northwestern most counties of the state with heavier precipitation indicated offshore to the west of Eureka. Inland across interior NorCal, clouds have begun to thicken to the north of Sacramento, while relatively clear skies to the south has allowed patches of dense fog to develop across portions of the Delta and in the northern San Joaquin Valley.

The front will accelerate southeastward across the region later today and tonight as the upper trough lifts into the PacNW. Snow will begin across the northern mountains this afternoon, and over the northern Sierra by this evening. Heavy snow and gusty winds will be likely in the mountains overnight as the front traverses the area, and snowfall rates may exceed 2 inches an hours at times overnight making for very difficult travel conditions. Snow levels will lower to 2000-4000 feet by Thursday morning, then lower to around 1500-3000 feet during the day.

A brief break in the precipitation will be possible early Thursday before a second impulse along with increased instability moves onshore. This will enhance mountain snow showers by Thursday afternoon and may also lead to a few thunderstorms across the Central Valley.

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Total snow accumulations will likely reach 1 to 2 feet across most of the interior NorCal mountain passes by early Friday. The low snow levels along with hefty snow accumulations will mean significant travel delays are likely with lengthy travel distances with chain requirements. If at all possible, travel over the passes this morning or delay until Friday or the weekend.

The return of ridging will lead to gradually drier weather Friday and heading into the weekend.

Extended discussion (Sunday through Wednesday)

Flat upper level ridging builds across interior NorCal Sunday, pushing the storm track to our north. Dry conditions will prevail across the forecast area Sunday into Monday. Forecast models indicate an upper level system moving inland for the beginning of the next work week. Best dynamics should remain to our north with only slight chances of precipitation over the northern mountains. Daytime highs will trend upward by early next week, but will remain near or slightly above seasonal normals through the extended forecast.