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

(06Z TAFS) Issued at 1028 PM PDT Wed Sep 30 2026

LIFR ceilings continue to impact coastal terminals through late Thursday morning with reductions to visibility becoming more prevalent overnight. Medium confidence for IFR to borderline MVFR ceilings to develop over the North Bay and south San Francisco Bay terminals early Thursday morning. Slightly lower confidence for STS to develop ceilings as denoted by the TEMPO group given the combination of a weak push of offshore flow and a compressed marine layer. Medium to high confidence for SJC and LVK to remain VFR through the TAF cycle. Onshore winds gradually ease overnight and increase to ~10-15 kt Thursday morning as stratus mixes out.

Vicinity of SFO...VFR as northwest winds gradually ease to ~5-10 kt overnight. Higher confidence for borderline MVFR-IFR ceilings to impact OAK compared to SFO. While a stratus deck is currently hovering over the San Bruno gap, the wind direction is unfavorable to allow it to fill over the terminal. Despite this, there is still a 50-60% chance for this deck to traverse over the terminal. Northwest breezes increase to around 15 kt Thursday early afternoon.

SFO Bridge Approach...Low confidence for widespread ceilings overnight. Cloud cover will likely be patchy in nature overnight.

Monterey Bay Terminals...LIFR conditions will continue to impact the terminals overnight with reductions in visibility due to mist or fog. Medium confidence on exactly when the drastic visibility impacts occur. VFR prevails mid Thursday morning into the evening before IFR ceilings move onshore again.

MARINE

(Tonight through next Tuesday) Issued at 1028 PM PDT Wed Sep 30 2026

Moderate to strong northwest breezes persist across the outer coastal waters with rough wind driven seas. Due to elevated seas, maritime conditions remain hazardous to small craft through Thursday, particularly over the outer waters north of Point Reyes. Northwest winds become gentle to moderate by late Thursday 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 Thursday for CAZ006-506- 508-529-530.

PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 3 AM PDT Thursday for Pigeon Pt to Pt Pinos 10-60 NM.