textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1211 AM PDT Thu Sep 17 2026

- Cooler temperatures continue today

- Warming trend Friday into the weekend

SHORT TERM

Issued at 1241 PM PDT Thu Sep 17 2026 (This evening through Friday night)

A cut-off low overhead allowed the marine layer to expand to nearly 5,000 feet this morning. This brought stratus to the vast majority of the Bay Area, where it still remains early this afternoon. The deep marine layer is also keeping temperatures around 10 degrees cooler than normal for this time of year.

The cut-off low will gradually weaken and move off the the NE over the next 24 hours. This will allow a short wave ridge to slide in from the west, increasing temperatures and compressing the marine layer Friday through Saturday.

LONG TERM

Issued at 1241 PM PDT Thu Sep 17 2026 (Saturday through next Wednesday)

Saturday looks like the warmest day of the weekend as the 500 mb short wave ridge axis moves over the Bay Area. There is also a hint of weak offshore winds, but the SFO-WMC gradient isn't expected to drop much below -2 mb. Another, much weaker, cut-off low will move over Sunday, dropping the temperatures a bit. Basically Saturday will be a couple degrees warmer than normal and Sunday will be a couple degrees cooler than normal.

It now looks like a steady warming trend arrives next week. The 850 mb temperature (measured at about 5,000 ft) is expected to hover around 20C (68F). That's around the 75th percentile for this time of year. Not enough for a major heat wave, but enough to bring surface temperatures 5-10 degrees above normal through the middle of next week.

AVIATION

(00Z TAFS) Issued at 551 PM PDT Thu Sep 17 2026

VFR everywhere with gentle to moderate onshore breezes around 5-10 kt with breezy terminals reaching closer to 15 kt. Diurnal onshore winds ease overnight and increase again Friday morning. As the upper level low moves eastward out of our area, the marine layer will gradually compress tonight, but will remain deep enough to reach all (if not, most) terminals. The pattern is rather complex, so there is currently low to medium confidence on the exact onset of stratus and ceiling heights. Medium confidence for ceilings to remain within MVFR territory with STS likely to be IFR. As high pressure builds in overnight, stratus is expected to scatter out by mid Friday morning.

Vicinity of SFO...VFR. Onshore winds ease overnight as the marine layer rolls in. Medium confidence on when MVFR ceilings develop. Some model guidance hints at the possibility of borderline MVFR-IFR ceilings around BKN007-010. The current TAF advertises BKN013-015 as significant compression is not expected overnight to allow for IFR ceilings. Stratus is expected to scatter out earlier around mid Friday morning as westerly winds increase.

SFO Bridge Approach...Similar to SFO, but may develop MVFR ceilings before SFO does.

Monterey Bay Terminals...VFR. Onshore winds ease overnight and shift south to southwest. Low to medium confidence on the arrival of stratus as well as ceiling heights given the complex pattern. The marine layer is not expected to compress significantly enough to dip into IFR territory, though it may be close. Stratus will scatter out by Friday morning earlier than it did today and a moderate onshore breeze around 10 kt will develop.

MARINE

(Today through Tuesday) Issued at 911 AM PDT Thu Sep 17 2026

Gentle to light breezes persist through Friday morning with mild seas across the coastal waters. A shift occurs Friday afternoon as northwesterly winds ramp up to fresh to strong breezes. Small Craft Advisories take effect Friday afternoon for Monterey Bay and the southern coastal waters from Pigeon Point south down to Point Piedras Blancas. Winds remain enhanced through the weekend, maintaining hazardous conditions for small craft while overall seas remain light to moderate through Sunday.

FIRE WEATHER

Issued at 421 AM PDT Thu Sep 17 2026

The coolest conditions and deepest marine layer are expected through the day today as the upper level low stalls over northern California. Current observations suggest a marine layer depth of over 3000 feet, allowing for moist conditions to reach very high into the higher elevations. As the low moves away on Friday, the marine layer will compress, temperatures will rise, and relative humidities in the higher elevations will start to decrease. Some offshore flow is possible on Saturday morning, but it is not expected to be very strong and the bulk of the offshore influence will be felt on the higher terrain of the North and East Bay.

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MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory from 3 PM Friday to 3 AM PDT Saturday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.

Small Craft Advisory from 3 PM to 9 PM PDT Friday for Pt Pinos to Pt Piedras Blancas 0-10 nm.