Bay Area residents can expect a noticeable shift in the weather pattern over the weekend as cooler, more humid air comes back, bringing relief after a spell of unseasonably warm and dry conditions. According to NWS San Francisco, inland temperatures today are above average by about 5 to 10 degrees, heightening fire weather concerns through this evening. However, an incoming upper level trough will bring temperatures down to around or slightly below normal as the new work week approaches.
The transition to cooler weather will be accompanied by a change in wind pattern, with the current weak offshore flow expected to swiftly shift to onshore by Sunday, according to a social media post by NWSBayArea. The organization shared satellite images to illustrate the return of the marine layer, a phenomenon often welcomed by coastal residents for its moderating effect on temperatures.
If you've been missing the marine layer, it's coming back this weekend. Weak offshore flow today, before next upper level trough brings a pattern change w/ robust onshore flow by Sunday. Left image is for late tonight, right image is late Saturday night. #calwx pic.twitter.com/BO8ntsikKN
— NWS Bay Area 🌉 (@NWSBayArea) October 25, 2024
Despite the welcomed shift, fire concerns remain through early Friday morning, especially at elevations above 1000 feet, where humidity recovery has been poor. The NWS San Francisco office noted that lighter winds at higher elevations continue despite gradually weakening the offshore pressure gradient. Fire weather conditions are expected to improve by Friday night as humidity increases with the deepening marine layer.
The steady onshore flow throughout the weekend and coming week will enable the marine layer to spread further inland. "Increasing coverage of morning stratus, patchy fog and drizzle along the coast with cooler than normal temperatures area wide through the remainder of the extended forecast," detailed in the forecast report by NWS San Francisco. This transition will also see higher humidity levels during the day and night, significantly reducing fire risks and potentially ushering in light rains in the North Bay.
Marine conditions are also set for a change as wave heights are expected to increase by Monday in response to the strengthening surface winds from the north/northwest. NWS San Francisco warns of significant wave heights reaching 10-12 feet in the outer waters. Meanwhile, aviation forecasts anticipate generally clear conditions with VFR (Visual Flight Rules) expected to prevail, but with the reemergence of marine stratus potentially affecting some terminals overnight into Saturday.
