textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 412 AM PDT Tue Sep 16 2025

- Dense Fog Advisory for portions of the Central Coast until 10AM

- Above normal temperatures with Moderate HeatRisk persists today and Wednesday

- Isolated to scattered thunderstorms possible Thursday into early Friday

SHORT TERM

Issued at 412 AM PDT Tue Sep 16 2025 (Today and tonight)

Areas of dense fog have developed overnight from the San Francisco Peninsula Coast south through Santa Cruz, Monterey Bay, the Salinas Valley and the Big Sur Coastline, with a Dense Fog Advisory out until 10am. Otherwise we're looking at another day with temperatures well above normal and widespread moderate HeatRisk, expect daytime highs today to be slightly higher than yesterday. Remember to remain hydrated with plenty of water and electrolytes, limit time outdoors during peak heating if possible, and never leave children or pets unattended in vehicles.

Keeping with the warm trend, overnight lows into Wednesday morning will continue to be above normal as well, with some elevated areas in the Bay Area, East Bay Hills, Diablo Range, and Santa Lucias remaining in the 70s with poor RH recovery.

LONG TERM

Issued at 412 AM PDT Tue Sep 16 2025 (Wednesday through Monday)

Wednesday will be the last day of the three day heat wave, with temperatures similar to todays highs and widespread Moderate HeatRisk. A pattern shift for Thursday and Friday into the weekend will continue to bring cooler temperatures, rainfall chances and elevated thunderstorm chances. However, there has been a not so subtle shift in guidance across the board in the most recent updates. Isolated to scattered thunderstorms remain in the forecast for now from the Bay Area south through the Central Coast during the day Thursday into early Friday. The upper level pattern has shifted quite a bit from Monday afternoons forecast update to this morning. An unusual synoptic pattern (a double Omega Block across CONUS?), agreed upon in numerous forms of deterministic guidance has the remnants of Mario becoming the more dominant feature as it lifts north into SOCAL. As a result, the bulk of rainfall and instability has taken a notable shift east and south away from our forecast area. That doesn't mean we won't see any showers or thunderstorms over the next 72 hours, but confidence is lower than it was yesterday and the trend appears to be drier. There is time for the forecast to whiplash back to wetter and more unstable for our area, especially across the Central Coast. But for now (including most recent 06Z GFS update, and slower northerly progression of 06z HRRR), it appears that Mario gets absorbed inland across SOCAL under the negatively tilted ridge axis from SE Oregon to southern Arizona. PWATs will still be well above normal and even if we don't see any rainfall it will feel muggy. We often say 'check back for updates', today is definitely one of those days.

AVIATION

(18Z TAFS) Issued at 1046 AM PDT Tue Sep 16 2025

VFR conditions have returned to most sites away from the immediate coast with KHAF still seeing LIFR ceilings/visibilities that should scattered out by 22Z. Onshore winds will increase this afternoon before easing after sunset and more so into Wednesday morning. High confidence of VFR conditions prevailing through the TAF period for the Bay Area terminals and LIFR conditions for the Monterey Bay terminals (and KHAF).

Vicinity of SFO...VFR. High confidence for onshore winds to increase this afternoon before easing into early Wednesday morning. High confidence for VFR conditions to prevail through the TAF period with increasing onshore winds once again Wednesday afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Onshore winds increase this afternoon before easing after sunset. High confidence for LIFR conditions to return to the region late evening and continue through about 16Z Wednesday.

MARINE

(Today through Sunday) Issued at 1046 AM PDT Tue Sep 16 2025

A gentle to moderate northerly breeze will prevail today, increasing to become fresh to strong for the northern outer waters Wednesday night into Thursday. Moderate seas will prevail today, building to become rough for the outer waters Wednesday through Friday. Isolated thunderstorms are possible Wednesday night and Thursday with isolated rain showers lingering through Saturday.

FIRE WEATHER

Issued at 624 AM PDT Tue Sep 16 2025

Near critical fire weather conditions for Tuesday thanks to hot, dry, and afternoon breezy onshore winds. To start the day active thermal belts in place with mild and dry conditions over the higher elevations. Overnight humidity recovery was moderate to poor with the highest peaks not even reaching 30% RH overnight. Ample sunshine and a warm airmass will yield temperatures well into the 90s and low 100s across the interior. Compound the heat with low humidity this afternoon in the teens to 20% range and typical gusts up to 20-25 mph will result in near critical fire weather conditions. Thereafter the forecast focus shifts to low confidence high impact scenario as tropical moisture brings a chance for elevated/high-based thunderstorms. The biggest concern will be the chance for dry lightning Wednesday into Thursday, which comes on the heels of a few days of hot/dry across the interior. We'll continue to assess the situation and coordinate with fire partners Tuesday morning before making any decisions regarding any Fire Watches.

MM

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.