textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1057 PM PDT Thu Sep 17 2026

- Warming trend through Saturday

- Brief cooldown Sunday

- Notable warming trend next week

UPDATE

Issued at 908 PM PDT Fri Sep 18 2026

Satellite imagery shows stratus clouds returning to the coastal regions from Bodega Bay down to Davenport and again from the Elkhorn Slough to Point Sur. There is also stratus flow into the East Bay west of the Berkeley-San Leandro Hills and through the Petaluma Gap. Latest observations suggest that the marine layer is beginning to redevelop at around 1000-1500 feet, allowing stratus to come rather far inland tonight.

DialH

SHORT TERM

Issued at 1120 AM PDT Fri Sep 18 2026 (This afternoon through Saturday)

The marine layer compressed to around 1,700 feet this morning. That trend will continue over the next 24 hours as a short wave ridge builds over the area. While the W-E gradients are all still weakly positive (SFO-WMC +1.9mb, SFO-SAC +1.2mb) we did see some NE, offshore winds this morning. The gradients will continue to drop and become negative this afternoon, however the onshore sea breeze will overpower any offshore flow during the day.

In response to the building ridge and compressed marine layer, Inland temperatures will be roughly 5 degrees warmer today compared to yesterday, and another 5 degrees warmer Saturday. While less expansive, the marine layer will continue to keep high temps along the coast in the 60s with low clouds and possible fog in the morning. The offshore wind gradient will peak overnight, though the strength still isn't overly impressive. Still, NE winds with gusts up to 20-30 mph are possible across the interior North Bay Mountains late tonight and early Saturday morning.

LONG TERM

Issued at 1120 AM PDT Fri Sep 18 2026 (Saturday night through next Thursday)

The pattern remains quite active in the long term forecast, although the next few features are pretty weak. Saturday's ridge is quickly replaced by a weak cut-off low approaching from the west through the day Sunday. This will reverse the warming trend and allow the marine layer to expand a bit. This low will gradually slide overhead by Monday morning, giving us a good chance for drizzle.

By Tuesday another ridge will start to build from the west, kicking off a warming trend that will last through the rest of the week. The ECMWF ensemble shows a 90% chance that the 850 mb temperature gets above 20C on Wednesday with a mean around 23C. 23C is above the the 90th percentile for this time of year and would bring inland surface temperatures back into the 90s.

AVIATION

(06Z TAFS) Issued at 1014 PM PDT Fri Sep 18 2026

Stratus is making its way inland bringing a mix of MVFR to IFR ceilings to most terminals tonight. Onshore winds ease overnight with their wind direction largely influenced by local terrain. By Saturday morning, winds shift onshore again and increase to moderate through the day. Most terminals will develop borderline MVFR-IFR ceilings and may intermittently jump between the two categories. Relied on persistence for STS with model guidance showing a high chance for another round of fog early Saturday morning. Low to medium confidence on whether APC, HAF, OAK, and MRY will drop to LIFR overnight. Current TAF hints at the possibility of borderline IFR-LIFR ceilings at the previously mentioned sites. Overall, medium confidence on the exact ceiling heights and clearing times. HAF might be the only terminal who does not clear on Saturday. If it does, it will be for a short period.

Vicinity of SFO...Ceiling heights may jump between MVFR-IFR through the course of the night with light onshore breezes. Medium confidence on exact clearing time on Saturday as ceilings may persist as late as 20Z (1 PM). Moderate westerly winds increase through the afternoon and ease by sunset. Saturday evening shows a promising return for stratus as early as sundown, though low to medium confidence on the exact return time.

SFO Bridge Approach...Delayed arrival of stratus tonight compared to SFO. Though, ceilings and wind pattern will generally be similar to SFO.

Monterey Bay Terminals...IFR ceilings have already filled over MRY and are slowly making their way over to SNS via current satellite imagery. LIFR ceilings may develop intermittently overnight with slight impacts to visibility. Onshore winds become light and variable overnight. As stratus clears tomorrow morning, a moderate onshore flow will develop through the afternoon. A similar stratus pattern is expected again Saturday evening.

MARINE

(Tonight through next Thursday) Issued at 908 PM PDT Fri Sep 18 2026

Moderate to fresh northwest winds persist through the weekend. Strong gusts up to 30 kt are possible across the northern coastal waters, Big Sur coastal jet region, and the Monterey Bay region through Saturday. Winds briefly diminish across the southern coastal waters Saturday morning, but increase again to fresh by Saturday afternoon. Slight to moderate wind driven seas prevail this weekend and steadily build to rough early next week.

FIRE WEATHER

Issued at 429 AM PDT Fri Sep 18 2026

The marine layer is expected to begin redeveloping itself through the day as a ridge develops over the state. By the evening hours the marine layer should be around 1000-1500 feet, along with attendant impacts of stratus development below the marine layer inversion and poor overnight humidity recoveries within and above the thermal belts. As the ridge develops, weak offshore flow is possible Saturday morning, particularly across the higher elevations of the North and East Bay.

DialH

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 3 AM PDT Saturday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 3 AM PDT Sunday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory from 3 PM Saturday to 3 AM PDT Sunday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.