Cooling temperatures for the work week, but it won’t last

Dry and not as hot through mid-week. High pressure strengthens bringing a return of very hot weather by the weekend.

Discussion

Some mid and high clouds are developing across interior NorCal early this morning ahead of the closed low to the southwest of the Bay Area. IR difference imagery still shows some heat from the Cow Fire east of Redding, but it’s not as pronounced as Sunday evening. Surface pressure gradients are trending toward onshore, and profiler data indicate the marine layer has deepened to around 2k ft. Current temperatures are mostly running a little cooler compared to 24 hours ago and generally range from the 50s in the mountain valleys to the 60s and 70s across the Central Valley.

High pressure will weaken a bit today and onshore flow will develop earlier helping to bring high temperatures down around 5-10 degrees compared to Sunday. It will still be hot across the northern Sacramento Valley where highs will around 100, and with min RH still forecast in the upper single digits to lower teens and breezy southerly winds, there will be a brief period of elevated fire weather conditions.

Moderating temperatures and humidity expected to continue Tuesday and Wednesday as the large scale pattern remains relatively unchanged with the closed low slowly deepening off the coast of the Bay Area.

Deep southerly flow is forecast to keep the shower and thunderstorm threat mainly to the north of the forecast area, the exception is tonight when some weak elevated instability is forecast over northern Shasta County which could result in some virga.

Uncertainty in the fate of the closed low increases toward the end of the week, but most ensembles favor retrogression as the western US ridge strengthens. Will continue forecast of beginning the next warming trend Thursday.

Extended discussion (Friday through Monday)

Closed upper low forecast to remain offshore through the extended forecast period as strong upper high builds over the Great Basin. This will result in dry weather with warming temperatures. Triple digit heat in the Northern Sacramento Valley Friday expands throughout the Central Valley over the weekend. Record heat is again possible early next week.