The National Weather Service (NWS) in San Francisco has issued a weather update providing the latest local conditions and forecasts. According to the NWS San Francisco, Bay Area residents can expect temperatures to remain near or slightly below seasonal averages with a cooling trend starting Tuesday. Meanwhile, the combination of dry conditions, gusty winds, and a stable marine layer heightens the fire risk across higher elevations.
Today's satellite imagery from the NWS reveals a stratus layer covering inland valleys and coastal regions as the marine layer sits at around 1500 feet. The marine layer should slightly compress as the day progresses, but some inland stratus will likely persist into the night. While morning temperatures hover in the 50s to 70s, depending on elevation, inland highs will climb into the 80s and 90s, potentially hitting 100 in the southern reaches of Monterey and Salinas and parts near the Central Valley. The Bayshore is forecast to experience a more temperate range of 70s to lower 80s, and downtown San Francisco is expected to hit near 66 degrees, with coastal areas seeing highs in the upper 50s to lower 60s. An onshore wind, gusting up to 25 mph in certain areas, will become a notable feature in the afternoon and evening.
The localized elevated fire weather threat results from a mix of low daytime humidities, between 20-35%, poor overnight recoveries, and localized gusts reaching 25 mph. While these conditions pose a significant risk, the winds are anticipated to remain onshore, suggesting that the fire threat will be primarily diurnal. Foothill regions, particularly where winds are lighter, will see better overnight recoveries, thereby slightly reducing risk each evening.
Looking ahead into the week, the short-term forecast anticipates similar weather conditions on Monday with a cooling trend commencing Tuesday due to a shortwave trough from the Pacific Northwest pressuring the ridge axis. This will lead to a drop in inland high temperatures to the mid-70s to 80s, and Bayshore regions will feel the cooler air with temperatures ranging from the upper 60s to the mid-70s. The coastal regions are anticipated to remain consistent, with highs in the upper 50s to lower 60s. As the week progresses, the forecast clarity declines, with ensemble models suggesting equal probabilities for either a warming trend or continued coolness heading into the weekend and early next week. The NWS San Francisco states that there is not enough confidence to diverge from the National Blend of Models (NBM) forecast, which anticipates a slow warming trend approaching the weekend.
For aviation, VFR conditions are expected to prevail in the afternoon following the morning's push of stratus, fog, and occasional drizzle. The San Francisco International Airport (SFO) will see stratus eroding by mid-morning, though low clouds could linger around the San Mateo County side. Westerly winds at SFO are predicted to intensify with gusts reaching 20-25 knots, then lessen later in the evening. IFR to LIFR cigs are again anticipated as the marine layer strengthens overnight.
Mariners in Bay Area waters should also be aware of the conditions at sea. Moderate breezes and slightly subsiding seas are forecast through Monday. However, come Tuesday, far northwestern portions of the northern outer waters will see stronger northerly winds and choppy seas, potentially reaching hazardous conditions. Winds are expected to calm by Wednesday, with more gentle to moderate breezes predicted through Friday.
