textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1230 AM PDT Wed Sep 16 2026

- Cooler temperatures through Thursday

- Warming trend Friday into the weekend.

UPDATE

Issued at 632 AM PDT Wed Sep 16 2026

The marine layer has grown to roughly 2,400 feet deep this morning, with widespread stratus coverage. The NW wind direction is supporting downslope drying over the Santa Cruz mountains, which is keeping Silicon Valley clear. Otherwise the morning clouds are reaching as far as Healdsburg, Dublin, and Pacheco Pass. There hasn't been any measurable drizzle yet. The clouds will start to pull back to the coast after the sun comes up.

SHORT TERM

Issued at 1208 AM PDT Wed Sep 16 2026 (Today and tonight)

Pretty easy to discern the longwave pattern over the region by taking a peek at the water vapor imagery. A wound up upper level low is digging over OR/CA border. The band of upper level clouds that streamed over the Bay Area the last two days has been shunted southward. Switching to a different satellite spectral band quickly shows what's happening at the surface as a result of the upper level pattern. Satellite fog product (difference of the 10.3-3.9 um IR bands) reveals decent stratus/marine layer coverage along the coast and pushing into the inland valleys. Per observational data depth continues to hover in the 1100-1500 foot range. No bucket tips as of yet, but cannot rule out some patchy drizzle along the immediate coast. Coverage and confidence isn't high enough to officially include drizzle in the forecast this morning.

Other weather highlights for Wednesday include temperatures and wind. The dropping upper level low is ushering in some colder 850mb temperatures. Colder temperatures aloft for September standard. As such, the airmass will support high temperatures in the 60s at the coast and 70s with a few low 80s inland. While it may feel nice, those values are 5 to 10 degrees below normal. The colder airmass aloft and surface pressure gradient orientations continue to promote gusty onshore flow this afternoon. Forecast captures this well and highlights gusty conditions along the coast, inland valleys, and inland gaps/passes (specifically Altamont/Pacheco Passes). The windiest spots could see gusts up 40-45 mph. Winds will ease late in the day and more so overnight as the onshore gradient relaxes.

For Wednesday night: given the lower 500mb heights overhead the marine layer will deep further and exceed 2000 feet with a run toward 2500-3000 feet by Thursday morning. Deep marine layer, onshore flow, and enhanced orographic lift will lead to higher confidence for widespread coastal drizzle. Despite the deeper marine layer it's not looking like a nocturnal drying set up, which is good from a fire weather perspective.

LONG TERM

Issued at 1250 AM PDT Wed Sep 16 2026 (Thursday through Tuesday)

Cloudy, cool, damp to begin the day on Thursday as the upper low lingers over NorCal. By Friday, the cut-off low exits to the NE with a weak shortwave ridge following for Saturday. This shift in the upper level pattern will have a shift in the sensible weather. The marine layer will compress slightly and temperatures will warm.

Longer range is lower confidence as yet another upper low begins to move through CA Monday. Expect another dip in temperatures, but albeit brief. Thereafter, the strength of the following ridge is uncertain. Regardless, current forecast does show warming through the middle of next week.

AVIATION

(12Z TAFS) Issued at 412 AM PDT Wed Sep 16 2026

Generally MVFR ceilings have developed across the region and are expanding into the interior valleys. Moderate confidence that LVK and SJC see ceilings at some point during the rest of the morning hours. Stratus will mix out rather late in the morning, with the coastal regions remaining socked in through the day. Some gentle to moderate onshore winds will develop in the afternoon and evening before MVFR stratus returns to the terminals in the evening and overnight hours.

Vicinity of SFO... MVFR stratus lies just to the north of the terminal area so have decided to keep the prevailing ceilings in the TAF for now. Stratus should begin to clear out in the later morning and early afternoon hours, but could persist to the north of the terminal. Low to moderate confidence that OAK remains socked in via the feed through the Golden Gate. Moderate west winds with strong gusts will develop in the afternoon and evening hours before MVFR stratus returns to the terminal in the evening through the end of the TAF period.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... MVFR ceilings persist through the late morning and early afternoon hours. Gentle to moderate west winds develop in the afternoon before diminishing in the evening. MRY sees a brief scattering in the afternoon before stratus returns in the early evening hours. At SNS, ceilings return a couple hours later.

MARINE

(Today through Monday) Issued at 412 AM PDT Wed Sep 16 2026

Moderate northwest to north winds prevail across the outer waters as occasional fresh to strong gusts gradually diminish by the afternoon. West to southwest moderate breezes dominate over the Bays with strong gusts resulting in hazardous conditions for small crafts late this morning through the evening. By Friday, widespread northwest to north breezes increase to fresh. Wind driven rough seas to 9 to 10 feet subside to moderate by the evening and will remain slight to moderate into the weekend.

FIRE WEATHER

Issued at 412 AM PDT Wed Sep 16 2026

A passing trough is allowing the marine layer to expand with the depth estimated around 2000-2500 feet in the area around the Timber and Plaskett Fires. Above the marine layer inversion, humidities remain low with relative humidity values as low as 15% observed. The trend for deeper marine layers is expected to continue into Friday, with humidities in higher elevations expected to rise as a result. Some nocturnal drying is possible in the highest peaks, but minimal coverage is expected.

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MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of Bay Bridge.

Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Mry Bay.

Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena to Pt Reyes 10-60 NM.