textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1243 AM PDT Sat Oct 3 2026

- Moderate to major HeatRisk across the Bay Area and Central Coast Saturday and Sunday

- Moderate to major HeatRisk across the interior Bay Area and Central Coast Monday through Thursday

- Elevated fire weather conditions across the higher terrain through Thursday

SHORT TERM

Issued at 1243 AM PDT Sat Oct 3 2026 (Saturday and Sunday)

The 00Z sounding observed an 850 mb temperature of 22.95 degrees Celsius and a 500 mb height of 5900 meters, both of these are above the 90th percentile. The heat will peak this weekend as an upper- level longwave ridge drifts in from the Eastern Pacific Ocean. A Heat Advisory will go into effect at 11 AM Saturday and run through 10 PM Sunday for most of the Bay Area and Central Coast. It was extended in area to include the Carmel Valley, Hollister Valley, Marin Coastal Range, Northern Monterey Bay, Northern Salinas Valley, and San Francisco. Now, the only places that are not included is the North Bay Coast, San Francisco Peninsula Coast, and Southern Monterey Bay; this is banking on a compressed marine layer keeping these spots cool. If the compressed marine layer is able to survive, expect reduced visibility from fog along the coast. If it is not able to survive, coastal conditions will be hotter than currently forecast. Moderate to major HeatRisk will result from maximum temperatures 10 to 20 degrees above normal. Minimum temperatures 10 to 20 degrees above normal with weaker than normal onshore flow will bring limited relief overnight, also contributing to HeatRisk. Even less relief is expected in the higher terrain where elevated fire weather conditions continue with hot and dry conditions, prominent thermal belting, and prolonged burn periods.

LONG TERM

Issued at 1243 AM PDT Sat Oct 3 2026 (Monday through Friday)

The Heat Advisory will remain in effect through 10 PM Monday for the interior Bay Area and Central Coast. Upper-level shortwave troughing will undercut the ridge and bring an increase in onshore flow Monday; however, the interior will remain hot. Global ensemble clusters are in agreement that heights will rebuild Tuesday and peak Wednesday. With little change in the day-to-day forecast and the cumulative heat impacts, we could be looking at an extended Heat Advisory. This is especially true for the East Bay and South Bay where major HeatRisk is likely (60%+) through Wednesday. The marine layer will remain compressed during this time, keeping the coast cool and likely reducing visibility from fog. Elevated fire weather conditions will continue in the higher terrain through Thursday for hot and dry conditions with prominent thermal belting and prolonged burn periods. Thursday remains uncertain on ridge vs. trough, but by Friday it is likely that heights will begin to fall.

AVIATION

(12Z TAFS) Issued at 512 AM PDT Sat Oct 3 2026

Satellite and surface observations show dense fog with surface visibilities less than 1/4 mile from the San Francisco Peninsula to the Big Sur coastline. Strong ridging aloft has compressed the marine layer to 500 to 700 feet. Away from the immediate coastline it's VFR. Marine fog is easier to see this morning with less high cloudiness obscuring the view, which is also allowing for improved nocturnal radiative cooling. It may radiate enough heat out to space through daybreak to allow a few patches of valley fog /IFR-LIFR/ to temporarily form across the inland valleys. However, the proximity of the warmth with the lower level temperature inversion is likely an offset, balancing to a higher valley floor air temperature making it more difficult to reach the dew point temperature (saturation).

HRRR output shows at least patchy low stratus and fog /IFR-LIFR/ along the coastline in the vicinity of the Monterey Bay area tonight and Sunday morning, otherwise VFR.

Vicinity of SFO...Low to moderate confidence VFR continues through daybreak without radiative cooling leading to fog development. VFR is otherwise forecast for the 12z TAF. Light west wind becoming light northeast this morning then northwest to west 7 to 13 knots in the afternoon and tonight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...With the loss of high cloudiness, radiative cooling will dominate through daybreak combining with residual cooler air relative to sea surface temperatures resulting in dense fog through 16z (9 am PDT). There's been some disruption in the fog due to cool air drainage winds and mixing. Diurnal mixing and the shallow depth of the marine layer i.e. a closer proximity to the lower level temperature inversion will produce sufficient mixing to erode the fog later in the morning. Otherwise VFR is forecast today. East to southeast cool air drainage winds around 5 knots KMRY and up to 10 knots at KSNS during the morning. Winds shifting to northwest 5 to 10 knots in the afternoon.

Low to moderate confidence low stratus and fog /LIFR/ return tonight and Sunday morning based on recent HRRR output. Winds becoming light and variable in the evening, then light east to southeast tonight and Sunday morning.

MARINE

(Today through Thursday) Issued at 426 AM PDT Sat Oct 3 2026

A shallow marine layer has resulted in areas of dense fog along the coastline to the Monterey Bay with visibility less than 1/4 mile. Dense fog will mix out later in the morning. Northwesterly breezes remain gentle to moderate into early week, allowing for slight to moderate seas to persist.

FIRE WEATHER

Issued at 458 AM PDT Sat Oct 3 2026

Hot and dry conditions are forecast through next week, which will be accompanied with weak offshore flow. Poor to very poor overnight recovery is expected for the thermal belts, generally for elevations above 1000-1500 feet, leading to elevated fire weather conditions. The marine layer is expected to be confined to the immediate coast and around 500 feet. A pattern change begins late Thursday into Friday, which may lead to cooler weather and the potential for improved RH recovery.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Heat Advisory from 11 AM this morning to 10 PM PDT Sunday for CAZ006-502-528-529.

Heat Advisory from 11 AM this morning to 10 PM PDT Monday for CAZ503-504-506-508-510-512>518.

Dense Fog Advisory until 9 AM PDT this morning for CAZ509-529- 530.

PZ...Dense Fog Advisory until 9 AM PDT this morning for Mry Bay.