December 25, 2017 – Generally dry conditions through the coming week with above normal temperatures. Mostly light winds.
Weak Pacific frontal system that brought a few sprinkles across northern California on Sunday has shifted south and east of the state this morning. High pressure building over the west coast will bring clearer skies and warmer temperatures today. Skies will not clear completely this Christmas day however with a weak trough off the coast spilling high cloudiness over the high pressure ridge and over NorCal most of the day. Still, daytime highs are expected to reach between 5 and 10 degrees above normal.
Overall little change is expected in the forecast from today on through the short term forecast period Thursday. Weather systems riding over the west coast ridge with bring more high clouds from time to time but daytime highs will remain fairly constant at several degrees above normal and morning lows coming in around normal. Surface gradient remains light northerly through much of the short term period but with upper flow mainly west or northwest, upper support is limited. Therefore only light northerly breezes are expected at times.
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Extended discussion (Friday through Monday)
High pressure over the eastern Pacific will continue to bring dry weather across much of the region through the weekend. A series of atmospheric rivers will likely be passing through the Pacific Northwest late this week, and one of these systems may sag southward enough to bring a bit of precipitation to far northern CA.
The upper ridge restrengthens over the region this weekend. Forecast confidence decreases early next week as the 12z ECMWF brings a closed upper low toward California, whereas the GFS continues the dry weather pattern.