Widespread triple digit heat returns to the Central Valley today with well above normal high temperatures through Wednesday. Cooling Thursday into next weekend. Chance of afternoon showers and thunderstorms over the Sierra Nevada today into midweek.
Discussion
Heights/thicknesses trend up today as upper high centered over the Great Basin builds westward. Marine layer is already becoming more shallow, down to around 1000 ft at the Fort Ord profiler under increasing subsidence. AMS warms today with 850mb temps rising around 3 Deg C above Sunday afternoon. Brought dry adiabatically to the surface equates to highs today in the Central Valley between 100 and 112, hottest in the N Sac Valley. As a result, widespread moderate heat risk expected with areas of major heat risk. Heat advisory in effect to address these impacts. Delta breeze also weakens today with limited cooling and have added much of that area to heat advisory. Monsoonal moisture associated with upper high and terrain influenced differential heating could bring a threat of afternoon showers or thunderstorms today over higher elevations of our N Sierra Nevada zone. Local areas of haze or smoke possible in vicinity of wild fires.
Model guidance showing high temperatures Tuesday will be near or slightly warmer for most locations. Areas of major heatrisk become more abundant Tuesday as overnight lows expected mainly in the 70s throughout the Central Valley with 80s in thermal belts of the foothills. Some monsoonal moisture depicted to spread into the southern half of the CWA Tuesday. Mid-level moisture then further increases over the CWA Tuesday night and Wednesday. This will result in keeping overnight lows Tuesday night a little warmer with a few degrees of cooling Wednesday. Delta breeze also looks to strengthen Tuesday night into Wednesday providing some cooling to influenced areas. Moderate heat risk depicted by NBM Wednesday with local areas of major risk in the Central Valley. Afternoon deep moist convection will continue to be possible over the Sierra Nevada tomorrow and Wednesday.
Offshore upper low progged to approach Thursday lowering heights over interior NorCal. Marine layer will continue to deepen and onshore flow increase. NBM showing about 2 to 6 degrees of cooling Thursday. Mid level flow turns more SWly diminishing afternoon thunderstorm threat over western portions of the N Sierra Nevada.
Extended Discussion (Friday through Monday)
Upper low progged to progress through the CWA Friday with model differences on strength and track of wave. Main impact appears to be synoptic cooling with increased onshore flow. Slightly below normal high temperatures expected Friday. Broad upper troughing remains over the area through the weekend resulting in below normal high temperatures through Sunday. Slight warming progged Monday as Desert SW High begins to strengthen and expand westward into CA. Dry weather forecast through the extended period.