December 12, 2017 – Dry and mild weather into early next week with chilly nights in the valleys.
Clear skies across interior NorCal except for a few high clouds. Current temperatures are similar to 24 hours ago and range from the teens in the mountain valleys, 30s to lower 40s in the Central Valley, and 40s to mid 50s elsewhere.
Strong ridge over the West forecast to retrograde to along the coast through mid-week, then a short-wave trough is forecast to flatten the ridge as it moves over the top on Friday. Precipitation associated with the wave on Friday is forecast to remain north of the region.
Little overall temperature change expected through the end of the week with dry and mild weather continuing under a strong subsidence inversion. Record high temperatures will be possible at the north end of the Sacramento Valley.
Chilly overnight temperatures will continue in the Central Valley beneath shallow nocturnal radiative inversions that develop each night with patchy frost likely.
Extended discussion (Saturday through Tuesday)
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Upper ridge of high pressure over the eastern Pacific and west coast will bring fair skies and well above normal temperatures on Saturday. A tight northerly surface gradient combined with an upper level northerly flow will bring breezy north winds most areas especially down the northern Sacramento valley. Upper ridge axis shifts over the west coast Sunday and Monday bringing continued warmer than normal temperatures while weakening surface gradients and upper level support bring lighter winds. Upper ridge begins to break down next Tuesday which should bring slight cooling trend going into mid week but daytime highs will remain above normal.