textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1156 PM PDT Wed Sep 30 2026

- Elevated fire weather conditions across the higher terrain Thursday

- Moderate to major HeatRisk across the interior through Wednesday

- Minor coastal flooding for bayshore locations along the San Francisco Bay, San Pablo Bay, and Monterey Bay Thursday

SHORT TERM

Issued at 1156 PM PDT Wed Sep 30 2026 (Thursday and Friday)

The 00Z sounding observed an 850 mb temperature of 21.75 degrees Celsius and a 500 mb height of 5880 meters; both of these are near the 90th percentile of 20.7 degrees Celsius and 5884 meters, respectively. The anomalously warm airmass will yield temperatures 10 degrees above normal with moderate HeatRisk for the interior. An impressive compressed marine layer will keep coastal locations cool and lead to reduced visibility during the overnight periods. Another morning of offshore flow with dry conditions will bring elevated fire weather conditions to the higher terrain. Gusts of 25-35 mph are expected with gusts up to 45 mph for the highest and most exposed peaks such as Mt. St. Helena. Minor coastal flooding for bayshore locations along the San Francisco Bay, San Pablo Bay, and Monterey Bay will occur during high tide Thursday afternoon. Depending on how Thursday's forecast verifies, the Coastal Flood Advisory may need to be extended through Friday evening, at least for San Pablo Bay if not all bays.

LONG TERM

Issued at 1156 PM PDT Wed Sep 30 2026 (Saturday through Wednesday)

Anomalously high heights, 90th percentile 850 mb temperatures and 500 mb heights, and EFI values of 0.90 or greater for maximum and minimum temperatures all point to it being hot across the interior Saturday through Wednesday. Global ensemble clusters are in agreement that the heat will peak Saturday as upper-level longwave ridging drifts in from the Eastern Pacific Ocean. An upper-level shortwave trough will skirt the region Sunday; however, it'll have little impact as it merely pauses the warming trend. Upper-level ridging will rebuild across the region from the east Monday through Wednesday. These subtle changes will have little impact on temperatures and HeatRisk with temperatures 10 to 20 degrees above normal and widespread moderate with areas of major HeatRisk expected across the interior. As is typical for heat events, the greatest uncertainty is at the coast due to the marine layer. As it stands right now, a compressed marine layer around 500 feet may be able to hang on. If it erodes or offshore flow develops in the mornings, coastal spots will be hotter than currently forecast. In terms of a Heat Advisory, it will likely be for a majority of the interior; the soonest it would be in effect would be Saturday with a chance for it to linger into early-to-mid next week. As a proxy, eastern San Francisco has a 90% probability of reaching 80 degrees on Saturday, followed by 70% on Sunday, and 50% Monday through Wednesday. Temperatures will cool off overnight; however, the weaker than normal onshore flow will bring less relief than normal.

AVIATION

(12Z TAFS) Issued at 516 AM PDT Thu Oct 1 2026

Conditions vary from clear /VFR/ inland to stratus and fog /IFR- LIFR/ along the coastline, in the coastal and inland valleys and across the San Francisco Bay. Conditions support stratus and fog, i.e. cooler air relative to sea surface temperatures, nocturnal radiative cooling to space (dry aloft) plus the longer night-time hours are bringing cool air valley drainage winds into the mix with cool winds gently flowing back to the coastline. Above this, the strong 500 mb ridge is producing a lower level temperature cap for the marine layer. The marine layer depth is currently 1000 feet. Above the marine layer it's 20F to almost 30F warmer (and drier). Since the marine layer is currently well structured per satellite and surface observations (and based on recent NAM, HRRR output) it'll likely remain a solid presence during the 12z TAFs. High and mid level clouds arrive tonight and Friday, which may slow stratus and fog mix out times Friday.

Vicinity of SFO...VFR except tempo stratus /IFR/ 13z-17z this morning. Stratus /IFR/ is likely to return tonight and Friday morning 06z-18z. High and mid level clouds arrive from the southwest tonight and Friday, caveat is these clouds may slow stratus mix out Friday. Light northwest to northeast wind during the morning, shifting to northwest and westerly 10 to 15 knots in the afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus and fog /IFR-LIFR/ during the morning, conditions improving to MVFR-VFR by late morning or afternoon. Stratus and fog /IFR-LIFR/ returning tonight and Friday morning. Light and variable winds except cool air drainage winds up to 10 knots e.g. in the Salinas Valley during the morning. Winds shifting to onshore 10 to 12 knots in the afternoon and early evening. Cool air east to southeast drainage winds redevelop tonight and Friday morning.

MARINE

(Today through Tuesday) Issued at 430 AM PDT Thu Oct 1 2026

Northwest winds will decrease and become gentle to moderate by late this morning, allowing seas to steadily abate to moderate by Friday. Marine conditions improve Friday into the weekend.

FIRE WEATHER

Issued at 502 AM PDT Wed Sep 30 2026

A high pressure system will move in from the west and compress the marine layer to approximately 500 feet. Hot and dry conditions will prevail through late week and weekend. Expect poor overnight humidity recoveries, with overnight relative humidities as low as 20-30% above the marine layer.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory until 5 PM PDT this afternoon for CAZ006- 506-508-529-530.

PZ...None.