Fall may arrive on the calendar at 11:19 a.m. Monday, but the Bay Area forecast has other ideas. Summer warmth will surge to start the week, with some of the hottest temperatures of the year possible Tuesday, before a midweek shift brings a shot at showers and thunderstorms.
Summer sneaks back in
The Bay Area will feel the heat Monday and Tuesday, with Tuesday having the potential to be the warmest day so far this year for San Francisco, which should see temperatures rise into the 80s East of Twin Peaks both days.
The general setup at the start of the week features a small “ridgelet” of high pressure sitting just north of an offshore cutoff low-pressure system. That bump in the atmosphere will pin the low in place and allow warm, dry air to spread over California.
The result is a classic offshore wind pattern with sinking air aloft and weak winds out of the east flattening the marine layer and letting heat spill all the way to the coast. The signal is especially strong Tuesday, when upper-air temperatures will run 3 to 6 degrees above normal for late September and the marine layer will have little chance to rebuild overnight Monday…