Dry weather with temperatures warming into the weekend. Chances for mountain thunderstorms return late weekend through next week.
Discussion
Broad high pressure is forecast to continue over much of the US through the weekend, stretching from the eastern Pacific into the Central US. This will keep temperatures around 5 to 15 degrees above normal for most of interior NorCal through Sunday. Expect Valley and foothill temperatures to top out in the mid 90s to near 110 degrees in the far northern Sacramento Valley with mountain temperatures in the 90s to 100 degrees. Mid-level monsoon moisture will begin to stream into Central CA Sunday, bringing a chance of thunderstorms to the Sierra around and south of Alpine and Tuolumne counties.
By Monday, ensembles indicate weak troughing will build off the coast in the Eastern Pacific, lowering heights somewhat over northern California and placing the area along the western edge of the monsoon high. This will allow temperatures to cool back to near normal by Monday and below normal Tuesday. A shortwave along the upper flow could bring instability and isolated mountain thunderstorm chances farther north into CA. On Monday, thunderstorm chances remain in the Sierra generally along and south of Interstate 80.
Thunderstorm chances could then spread north into the mountains and foothills of Shasta County and the Coastal Range overnight Monday into Tuesday. PWAT values are forecast around 0.75 to 1 inch, so thunderstorms shouldn`t be dry. The main impacts with any thunderstorm would be gusty winds, brief heavy showers, and lightning. Those spending time outdoors this week should be weather aware.
Extended Discussion (Wednesday through Saturday)
Little change expected for the second half of next week into next weekend. NorCal will remain on the periphery of strong high pressure centered over the central US. Moisture moving westward under the ridge will continue a chance for mainly diurnal deep convection over the mountains. Temperatures will be a little above average.