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December 16, 2017 – Windy dry conditions today into tonight with wind advisories and Red Flag warnings in place. Decreasing winds Sunday. A chance of light rain or showers mainly over the mountains mid week. Otherwise dry conditions through the end of next week.

Discussion

Upper trough axis now making its was through the northern Sierra with a few light showers showing up on Radar. Only a few trace amounts of precipitation have been reported. Clearing over the central valley has allowed areas of fog to form there. Northerly surface gradient is increasing and already over 10 mb from MFR to SAC. Red Bluff is already seeing sustained winds of 20 knots. Lighter north winds are occurring farther south and these winds will be on the increase today as the upper level northerly flow mixes down. Surface gradient maxes out this afternoon at over 15 mb from MFR to SAC. Predicted 925 mb winds are at 30-40 knots. Strongest winds are forecast to be from the central Sacramento valley west and southward.

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Combination of Low RH and strong north wind will reach Red Flag criteria over the coast range while the strongest winds will occur down the central valley. Meanwhile, cool advection will bring daytime highs down to near normal despite clearer skies today. Surface gradients weaken overnight but breezy north winds will continue. Lighter but still breezy north winds will continue on Sunday and there will be warming as the upper ridge axis centers over the west coast. Warm conditions and lighter winds continue Monday and Tuesday as the upper ridge slides over the west coast. An upper trough dropping out of the Pacific Northwest may bring a chance of rain to the northwest corner of the state by Tuesday night or early Wednesday of next week.

Extended discussion (Wednesday through Saturday)

Confidence is improving that a cold upper trough from the Gulf of Alaska will move through the region on Wednesday bringing the potential for showers, mainly for the foothills and mountains. Precipitation is expected to be minimal. Gusty north winds will likely develop through the Central Valley in its wake later next week.