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December 7, 2019 – A strong winter storm will bring periods of heavy rain, mountain snow, strong winds, and hazardous travel this weekend. Dry conditions return next week with near average temperatures.

Discussion

The closed low is currently sitting at 130W this morning with one embedded disturbance moving into southern OR. Radar imagery does show a quite a few showers over interior NorCal, with the bulk of the precip currently located over NW CA. Expect to see increasing chances for precip again later today as the next wave moves in. This will bring periods of moderate to heavy rain and mountain snow, along with the chance for some Valley thunderstorms.

Instability, shear, LI, and a favored vort max support the chance for storm activity. HREF probabilities continue to high light the potential for over a half inch of rain an hour for portions of the foothill and Valley regions. Some blesses form over Lake and Butte counties in particular, thus we kept the Flash Flood Watch going for the the Carr/Hirz/Delta, Camp, and Mendocino Complex burn areas.

For those also, or perhaps more interested in the snow forecast, snow levels are expected to be around 6500-7000ft throughout most of the day, but will slowly be falling this evening. The profiler at Colfax this morning depicts snow levels around 7500ft. Expect to see moderate to heavy mountain snow over the Sierra Nevada today, especially for areas above 6500ft. Significant travel impacts are expected. Gusty winds may create near white out conditions at times in combination with heavy snowfall rates. Snow levels do drop slightly by early Sunday morning as the low moves over NorCal, with snow down to about 5500-6000ft. Feet of snow are still expected by the end of this system. The Winter Storm Warning continues through early afternoon Sunday.

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Finally, we can expect to see breezy winds continue in the Valley through much of the morning and into the early afternoon hours. Wind gusts of 30-45 mph will be possible, mainly for the northern portion of the Sacramento Valley.

Looking to Sunday, showers will linger over the area with the possibility for some isolated thunderstorms, mainly south of HWY 36. As the mid level wave pushes out of NorCal chances for precip will dwindle, with drier weather expected for the evening. Ridging returns Monday with average temperatures and dry weather expected through Tuesday.

Extended Discussion (Wednesday through Saturday)

Ensemble guidance continues indicate zonal flow across the eastern Pacific later next week with ridging across NorCal. The pattern will bring potential for light warm-advection precipitation across the northern mountains, but the remainder of the area will likely remain dry. Temperatures will be slightly above average.