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.
(00z TAFS) Issued at 446 PM PDT Tue Aug 4 2026
A more robust marine layer than the previous few days/nights remains mostly constrained to the coastline this afternoon but will begin to make its way inland around sunset tonight, with all terminals expected to see at least a short period of IFR/LIFR ceilings through Wednesday morning into the early afternoon for some.
Vicinity of SFO, IFR/LIFR ceilings are expected to spread over the Bay Area later this evening into the overnight hours with a more organized marine layer and breezy onshore flow helping stratus to spill over into the Bay Area by midnight. VFR conditions are expected by early afternoon, with a local offshore circulation (Otter Eddy) resulting in more variable wind directions at times through most of the forecast period.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, VFR currently, however stratus is already spilling into the Salinas Valley and the Monterey Peninsula in vicinity of both terminals. Once ceilings settle in, IFR/LIFR is expected to persist through at least late morning, and possibly into early afternoon.
(tonight through next Sunday) Issued at 446 PM PDT Tue Aug 4 2026
Light to gentle breezes will persist across the majority of the coastal waters through late week. A localized gentle to moderate breeze continues across the inner waters. Seas continue to abate through Thursday with wave heights between 4-8 feet expected through Friday. The Pacific High strengthens and shifts eastward late this week into the weekend, resulting in strengthening winds and building seas with a return of hazardous conditions for small craft.
Ca, None. PZ, None.
