November 4, 2016 – Patchy morning valley fog, otherwise dry today with slightly above normal temperatures. Cooling over the weekend with rain chances Saturday night into Sunday, mainly north of interstate 80. High snow levels above passes. Mainly dry with warming to near normal through midweek except a slight chance of light rain brushing the Coastal Range and Western Shasta county early Wednesday.
Large upper ridging centered over the Rockies extends westward over NorCal. Moist boundary layer, subsidence, clearing skies, and light wind have allowed some patchy fog to develop from around Oroville southward to Stockton. This will be short lived and should dissipate later this morning. Fair skies across the forecast area today with high temperatures in the lower to mid 70s in the Central Valley with upper 50s to lower 70s for the mountains and foothills.
Deep trough in the EPAC and associated frontal system approaches the West Coast early Saturday with frontal precip spreading into the Coastal Range Saturday afternoon. Increasing cloudiness Saturday will help lower temperatures with greatest cooling expected in northern portions of the CWA.
Front and associated upper trough moves through tomorrow night into Sunday morning. Models continue to show bulk of precip mainly north of I-80 with QPF ranging from around half an inch in the Shasta mountains tapering down to a hundredth or so around the Sacramento area. Snow levels forecast to remain above pass levels through the event. Precip winds down Sunday as subsidence increases over Interior NorCal. Additional cooling expected Sunday with high temperatures near to slightly below normal.
Heights gradually rise over Interior NorCal early next week initiating a slow warming trend and drier weather. High temperatures expected to be near to slightly above normal Monday into Tuesday.
Extended discussion (Tuesday through Friday)
Upper ridging is in place over the Great Basin early next week with dry southwest flow across NorCal. The GFS shows a weakening shortwave system moving into northwest CA sometime late Tuesday into early Wednesday, while the ECMWF keeps a drier, steady southwest flow. At any rate, we restricted the chance of showers to the Coastal Range and Shasta County Tuesday night. Temperatures will be near to slightly above average during the extended period.
By next Friday or Saturday models bring the next wave into NorCal with the next chance of precipitation. This far out the models diverge significantly; the GFS is about 18-24 hrs faster (Friday) than the ECMWF (Saturday).