Hot weather gradually builds this week, peaking over the Labor Day weekend. A few thunderstorms will be possible over the Sierra south of Lake Tahoe this afternoon.
Discussion
Some mid and high clouds associated with the closed low to the southwest of the Bay Area cover portions of the region early this morning, but overall skies remain clear. Little change noted in surface pressure gradients or the depth of the marine layer compared to early Sunday.
Current temperatures are running about the same as 24 hours ago and are mainly in the 60s across the Central Valley, except lower to mid 70s over the northern half of the Sacramento Valley.
The low is still forecast to open and lift northward today. Enough elevated moisture/instability present that virga, or sprinkles, cannot be ruled out. The Sierra south of Tahoe may see a few late- day thunderstorms along the crest.
After that, the focus for the remainder of the week will be on the return of widespread triple digit heat for the lower elevations after mid-week as strong high pressure over the western US builds westward into NorCal.
Extended Discussion (Friday through Monday)
Ensemble guidance and cluster analysis indicate anomalous ridging strengthening over the region through the extended forecast period. In addition, the ECMWF EFI suggests anomalous heat during this time frame. Triple digit heat is expected in the Valley, with 80s to 90s in the mountains.
Little to no overnight relief is expected, with lows ranging from the upper 60s to upper 70s. Therefore, widespread moderate to locally high heat risk is anticipated across interior NorCal. Those with outdoor plans should plan accordingly to prevent heat-related illnesses.