June 1, 2021 – Well above average temperatures with generally dry conditions continue. Temperatures lowering slightly by the weekend. Scattered mountain thunderstorms possible Wednesday and Thursday afternoon.
Temperatures have cooled down into the 60s across the Sacramento and Delta region early this morning. The Delta Breeze will continue throughout the day and will keep temperatures in Delta influenced areas lower than 24 hrs ago. Elsewhere areas in the San Joaquin Valley south of Stockton as well as The Sacramento Valley and surrounding foothills north of Yuba City will continue to see well above average temperatures and continued heat risk.
Therefore, those areas will remain under an Excessive Heat Warning through Tuesday and portions of the Northern Sacramento Valley through Wednesday. The very dry airmass in place over Northern California will also continue under upper level ridging.
Ensemble guidance is in good agreement the ridge axis is forecast to slowly shift to the east of the region by mid week as an upper level low makes its way to the Pacific Northwest.
We could see some mountain thunderstorms develop over the Sierra and Southern Cascades Wednesday and Thursday afternoon. Current model guidance indicates the area with the best chance to get some isolated thunderstorms will be south of Hwy 50 and east of the crest. We will also see increased onshore flow and lowering temperatures.
Extended discussion (Saturday through Tuesday)
Hot and dry weather continues Saturday as strong ridge remains over NorCal keeping highs around 10-15 degrees above average. Long wave troughing then develops over the PacNW into the second half of the weekend into early next week. Ensembles are not in good agreement with placement and timing of this trough, but it should bring continued cooling to the region. This pattern will support onshore flow and moderate Delta breezes.