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Another weather system moves through the region today bringing renewed precipitation chances. Dry weather returns for the weekend into next week. Winter Weather Advisory from 6 AM this morning to 6 PM PST this evening for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

Discussion

Surface pressure gradient is tightening ahead of the approaching front (currently nearing the northwest coast of California), and southerly breezes are beginning to pick up across the north end of the valley and over the mountains. Current temperatures range from the 30s to lower 40s in the mountains, to the upper 40s to lower 50s across the Central Valley.

The system will move southeast fairly quickly today. The front is expected to be near the I-80 corridor around midday, then southeast of the forecast area by this evening. A period of several hours of moderate precipitation (especially in the mountains) can be expected as the front approaches and moves through.

Snowfall accumulations of around 2-6 inches are likely across the higher elevations of the northern Sierra/southern Cascades. Scattered showers, with perhaps a few thunderstorms, can be expected behind the front during the afternoon.

Forecast soundings don’t look too bullish on instability, but a few hours of clearing behind the front along with the upper trough swinging through in the afternoon may be enough to pop a few storms over the northern Sacramento Valley and surrounding terrain.

Remaining showers are forecast to end this evening as the system moves out, then cool and dry weather is forecast over the weekend with northerly surface flow. Patchy morning fog and frost will be possible, especially along the eastern edge of the valley sheltered from the north winds.

The ridge is forecast to weaken and shift east on Monday allowing clouds and moisture to return, but confidence in any light precipitation is very low.

Extended Discussion (Tuesday through Friday)

Ensembles show an upper level ridge building across the Western U.S. during the extended period, resulting in dry conditions. The ridging pattern would be favorable for areas of night and morning Valley fog.

Forecast highs will remain near or slightly above normal with Valley temperatures in the mid to upper 50s. A weak disturbance may brush the region around mid-week, but not expecting much precipitation associated with this system.