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March 16, 2018 – Unsettled weather today into Saturday with showers, possible afternoon thunderstorms, and moderate to heavy mountain snow showers. Drier Sunday into Monday, then wet weather returns next Tuesday into Friday.

Discussion

533 DM upper low situated off the ORCA border this morning will slowly fill as it moves into Interior NorCal this afternoon into evening then into Great Basin Saturday. Cyclonic flow and embedded vorticity maxima rotating into the forecast area will keep unsettled weather today and Saturday.

Showers and possible thunderstorms are expected in the Central Valley and foothills along with continued snow showers in the mountains. Snow radar at Oroville and Colfax this morning showing snow levels currently around 3500 to 4000 feet, while mesowest data suggesting snow level around 2500 feet in the Shasta mountains.

Additional 2 to 6 inches, locally up to 10 inches of snow is possible in the Coastal and Shasta mountains, with 1 to 3+ feet in the mountains of Western Plumas county and Sierra Nevada through Saturday.

Little change in snow levels today, lowering another 500 to 1000 feet tonight into Saturday.

High temperatures in the Central Valley continue about 10 degrees below normal today and tomorrow.

Upper troughing shifts east tomorrow night with upstream ridging beginning to build inland. Thus showers expected to diminish at that time, with mainly dry weather Sunday. Models showing a weak upper trough moving through upper ridge Sunday afternoon into night bringing a slight chance of a light shower to the higher elevations of the Coastal, Shasta, and Western Plumas mountains. Upper ridge strengthens Monday bringing drier and warmer weather to Interior NorCal.

Extended discussion (Tuesday through Friday)

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Models continue to slow down Pacific storm system expected to move into NorCal early next week. Even the ECMWF which is a bit faster than the GFS keeps Tuesday dry for most of the forecast area. If current timing holds then the coast range may get a bit of precipitation by Tuesday afternoon. Daytime highs Tuesday should warm a bit up to just slightly under normal for this time of year. Relatively light precipitation moves into the north state Tuesday night. Moderately high snow levels, generally above 5000 feet, combined with light snowfall should keep mountain travel impacts to a minimum.

A subtropical moisture tap will push northward into NorCal on Wednesday increasing the rain and snow rates. Snow levels Wednesday will remain relatively high but amounts of snow will now be significant enough at pass levels to start causing Sierra travel issues again. Moderate to heavy precipitation continues into Thursday before turning more showery on Thursday night and Friday as the main upper through drops into the Pacific Northwest. Snow levels during this time will drop back down to relatively low for this time of year but precipitation amounts should be on the decrease.