Cooling trend this week. Smoke from area wildfires will persist over portions of interior NorCal. Shower chances return this weekend.
Discussion
Clear to partly cloudy skies cover the region early this morning. Onshore flow continues, though the surface gradient from the coast to the valley has slackened since Tuesday afternoon. The cooling trend continues with most readings running around 5-10 degrees cooler compared to 24 hours ago.
Current temperatures are in the upper 50s to mid 60s across the Central Valley. Most portions of the Central Valley are seeing RH up around 15-30 percent, while many mountain areas above about 4k ft are seeing RH lower by about 10-20 percent, since early Tuesday.
Ensembles maintain the cooler pattern with a weak trough through the remainder of the week. Temperatures will be around 5-15 degrees below average with locally breezy southwesterly winds. Shower chances will be south and east of the area.
Smoke from the Mosquito Fire will mostly be transported off to the north and east. A deeper trough is forecast over the weekend, and southwest winds are expected Saturday as it approaches.
Precipitation and even cooler temperatures will likely hold off until later in the weekend.
Extended Discussion (Sunday through Wednesday)
Unseasonably deep upper low invades the West Coast Sunday with models continuing to generate areas of associated precip over interior NorCal. System will usher significantly cooler air with highs Sunday upwards of 20+ degrees below normal. Some light snow accumulations possible above 7500 feet.
Upper low continues to dig to the SW Monday and closes off, off the Central CA coast. This then leads to model uncertainties in how quickly it will progress. Forecast for now continues a threat of showers Monday over the eastern foothills/mountains, and southern portion of the Central Valley.
Drier weather expected Tue/Wed with warming trend and some locally gusty north to east wind.