Widespread dangerous and excessive heat into early next week

Dry conditions are forecast to continue with very hot temperatures expected by the end of the week continuing into early next week. An Excessive Heat Warning is in effect for much of interior NorCal Friday afternoon through Monday evening when the hottest weather is expected.

Discussion

Westward drift of the 4-Corners High pressure cell will allow for the WNW expansion of the ridge into NorCal and another impressive heat wave for Norcal Fri-Mon.

The hottest days appear to be this weekend when 850 mbs temperature anomalies exceed 2 over the Central Valley, and are forecast to reach 30-31 deg C in the Valley.

Usually these temps are to our east, but the WNW expansion of the 4-Corners high has pushed them farther W and into the Valley. Dry-adiabatic descent of this air pushes the max temps into record/near record territory, with only cloud cover or wind direction as a limiting factor.

The NBM forecasts RDD to tie or be within 1 degree of a record this weekend, and we have also included DTS in this morning’s forecast on Sat wrt to the ECMWFs Extreme Forecast Index (EFI), with potential for Sun as well as 850 mbs temps continue to run anonymously hot, and the 1000 mbs 40 Deg C isotherm remains in the proximity of the Srn Sac/Nrn San Joaquin Valley.

A more southwesterly wind flow on Sunday may keep the SAC area from a record, instead of the westerly flow on Sat.

Due to the anonymously hot 850 mbs temps, thermal belt areas will be extremely warm overnight, where high minimum temp records may be achieved as well.

By Monday, the extreme anomalies are easing and by Tue/Wed there is enough of a synoptic change to end the excessive heat.

Thunderstorm activity looks virtually nil for our CWA the next couple of days, except on Sun where instability nears the Crest in the Tuolumne/Alpine County areas.

Extended Discussion (Monday through Thursday)

Upper ridging over interior NorCal flattens through the extended forecast period as short waves progress into the PacNW. This will result cooling next week with increasing onshore flow.

High temperatures trend down from about 10 degrees above normal Monday to near normal by Thursday.