Hot weather will continue, peaking Thursday into the start of the weekend with breezy winds through the Delta at times. Slight chance for isolated afternoon and evening thunderstorms across the High Sierra south of Highway 50 at times.
Discussion
We are seeing some mid to high level clouds move through the area this afternoon. This is associated with some weak vorticity over the region and residual monsoon moisture. An isolated shower or t-storm can’t be ruled out at the Sierra crest in Tuolumne County. If anything would develop it would be weak and brief.
Clouds will dissipate overnight with mostly clear skies. Otherwise high pressure will be building over the region into the start of the weekend and will bring hot conditions.
Highs are going to soar well above 100 in the northern Sacramento Valley Thursday and Friday with the hottest highs as hot as 113. 850 mb temps stay very warm overnight in the 26-29C range, this would indicate upper 70s to even some mid 80s in the thermal belts overnight.
Overnight lows over the northern Sacramento Valley outside the thermal belts will also be warm in the 70s. Given the very hot daytime highs and warm to hot overnight lows an Excessive Heat Warning has been issued for for the northern Sacramento Valley, adjacent foothills, Shasta County Mountains, and the Burney Basin.
Hot conditions are expected outside of the heat product but onshore winds and a good Delta Breeze will help to keep daytime highs more reasonable and will bring good relief overnight. As the high builds in overhead it will push any monsoon moisture south for Thursday and Friday. This will limit any thunderstorm chances but a few afternoon clouds over the mountains can be expected. The ridge will begin to push east on Saturday and that will bring the start to slight cooling.
Extended Discussion (Sunday through Wednesday)
Monsoonal moisture is forecast to push into NorCal for the first part of next week and could bring some isolated thunderstorms to higher elevations of the Sierra south of Highway 50 Sunday through Tuesday. Precipitable Water values look to be high enough that any thunderstorms that do form should produce wetting rains, lowering the concerns for dry thunder.
A trough of low pressure will move towards the west coast and will bring slightly cooler temperatures (Valley temperatures in the 90s) and continued onshore flow. However, there is quite a bit of disagreement in the clusters on the timing and strength of this trough.