Issued at 911 PM PDT Tue Aug 4 2026
The Heat Advisory for the East and South Bays was just cancelled due to temperatures cooling and the marine layer seeping into the the region. Expect the marine layer to get to around 1000ft tonight, perhaps even closer to 1200ft given the expansion we've already seen. This should help bring low temperatures into the 50s for much of the region, with those above the marine layer and the thermal belts remaining dry and warm. The forecast for tomorrow looks to be on track.
, Issued at 109 PM PDT Tue Aug 4 2026 (This evening through Wednesday night)
Rest of today: Marine layer rolled back to the coast, but is hanging pretty solid along the coastline. Lingering marine layer plus a slightly stronger onshore flow equals an impressive 24 hour trend. Temperatures as of 1 pm are currently running a few degrees cooler to as much a 20 degrees than Monday. Warmest locations in the forecast area are across the interior with temperatures still in the mid 90s to low 100s even with the cooling trend. Will keep Heat Advisory as is for now through 10 PM, but it does appear some spots may fall short of their forecast highs.
Additionally, visible satellite imagery also shows smoke lurking over the coastal waters. This smoke is actually from the PacNW fires. Latest smoke model brings some high level smoke over the Bay Area later today, which may contribute to some haze or just a pretty sunset.
Tonight through Wednesday night: Marine layer along the coast will March inland again tonight. Have added another round of coastal drizzle. Depth of the marine layer will remain around the 1k ft mark. Above the marine layer will remain mild and dry with active thermal belts.
The cooldown experience today will continue on Wednesday thanks to persistent onshore flow, marine layer influence, a weak disturbance overhead riding the periphery of the upper ridge. Event with a "cooldown" far interior locations will be well into the 90s with a few making a run at 100 degrees. High probability of exceeding 100 degree will be interior Monterey/San Benito counties and far interior East Bay. Given the slightly cooler temperatures HeatRisk values decrease. As such, will not be issuing a Heat Advisory at this time for Wednesday.
Wednesday night will feature another solid push from the marine layer, but maybe a tad more compressed given building H5.
..issued at 148 PM PDT Tue Aug 4 2026 (Thursday through next Monday)
Thursday will be a transition day as marine layer compresses and the upper level ridge makes its presence known again. Temperatures will be moderating with a large difference with cool temps at coast and much hotter temperatures inland. Basically, in the big picture nothing major from what we've been seeing. Just that temps will be cool enough to keep HeatRisk values in the Minor to Moderate categories.
Friday through Saturday, the upper level ridge begins to re-assert its dominance with building 500mb heights and warming 850mb temps back to critical levels. The building H5 will further compress the marine layer. The marine layer will remain however. Really need offshore flow to get rid of the marine layer at this point. 850mb temps soar back into the 28-30C range, yielding inland max temps in the low 100s and overnight lows in the 70s. That combo will increase HeatRisk back into the upper end of Moderate to lower Major. Therefore, we'll likely need a mix of Heat Adv for interior locations Friday/Saturday. Still looking above normal at the coast/bays, but natural AC will keep the real heat inland.
Interesting longwave pattern in the extended as the upper level ridge looks to become more "split" with a system sweeping through PacNW. The easing upper level ridge will allow for subtle cooling across the interior for Sunday and Monday. We'll need to take a closer look if any Heat Adv will be needed on Sunday since heat impacts are cumulative.
(06z TAFS) Issued at 1012 PM PDT Tue Aug 4 2026
Stratus has begun a somewhat triumphant return inland after sunset tonight. Monterey Bay will soon be IFR/LIFR for the remainder of the night into Wednesday morning. North Bay, Bay Area and South Bay terminals are VFR for the moment but should follow suit by midnight except for South Bay sites, which will take longer, closer to sunrise. A more organized marine layer around 1000ft maybe as high as 1500ft for some spots, is spilling over the terrain into the North Bay attm. A surface trough enhanced by thermal troughing this afternoon and evening continues to pull stratus farther inland through the Golden Gate into the bays, with more of the same farther south into Monterey Bay.
Vicinity of SFO, Similar to SFO.
SFO Bridge Approach, Currently VFR, and while the stratus continues to fill in through the Golden Gate, it will take more time to fill in around KSFO, considering it has already begun surrounding KOAK. An offshore meso- low (Otter Eddy) will linger up and down the coast north of the Golden Gate tonight and tomorrow, which will result in light and variable winds at times, occasionally more established from the south and west. A decent thermal inversion (H85 25-27C through the morning) and gradual increase surface pressure under the inversion may trap the stratus a little longer than guidance is suggesting.
Monterey Bay Terminals, Expecting IFR/LIFR through the remainder of the night with a more normal diurnal lifting to VFR than farther north, by early afternoon. The window for VFR may only be 4-5hrs long with stratus expected to return well before sunset early Wednesday evening.
(tonight through next Monday) Issued at 1012 PM PDT Tue Aug 4 2026
Light and gentle breezes will continue over the outer and coastal waters through the work week along with seas between 4-8ft. Winds will begin to increase again out of the northwest going into the weekend with building seas and hazardous conditions for small craft returning.
Ca, None. PZ, None.
