textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 2 PM PDT Wed Aug 5 2026

- Elevated fire weather threat across the interior North and East Bays, and the Diablo and Santa Lucia ranges through midweek.

- Widespread Moderate and areas of Major HeatRisk returns for the end of the work week.

- Critical fire weather conditions develop Friday and Saturday.

SHORT TERM

Issued at 200 PM PDT Wed Aug 5 2026 (This evening through Thursday night)

While not as extreme as yesterday, today's 24 hour trend still indicates a downward trend of an additional 2 to 10 degrees. Persistent onshore flow and lurking marine layer led to additional cooling observed today. A welcomed relief for the interior to get a break before the next round of heat.

Tonight through Thursday night: Despite high pressure overhead the marine layer will continue to be the main driver of overall weather in the Bay Area and Central Coast broadly speaking. Clouds will move inland at night and clear back to the coast in the afternoon. Greatest impact of the marine layer will be near the coast/bays and lower elevations. Thermal belts remain active with the hills remains mild and dry through the short term. Thursday will once again feature a broad range of temps from the coast to the interior.

Onshore flow will also bring some breezy winds each afternoon/evening. Additionally, some high level smoke may lead to some haze.

LONG TERM

Issued at 230 PM PDT Wed Aug 5 2026 (Friday through next Tuesday)

No significant changes for Friday through the weekend from previous forecast. The upper level ridge will flex again over the region bringing higher 500mb heights and even warmer 850mb temps. As a result of the large synoptic set up we'll see the following in response: compression of the marine layer, increase of temperatures through Saturday and then moderating on Sunday, increasing HeatRisk values to include Major, decreasing RH, and enhancement of the thermal belts. Less confident for a Heat Advisory across the interior on Friday, but very confident we'll need a Heat Advisory on Saturday. It's also possible that we may need one on Sunday as well since heat impacts are cumulative and we'll be day three of the warm up. Starting to sound like a broken record at this point, but the onshore flow/marine layer will keep the natural AC at the coast/bays. We'll see above normal temps, just not to critical levels. The upper level ridge eases its grip by Monday/Tuesday with subtle cooling as the heat shifts back toward the Central Valley.

One other item of note for the long term will be the influx of upper level moisture. Guidance still shows a solid push of high PWAT air from SoCal. The leading edge will nose in as early as Thursday, but the bulk of it will arrive Thursday night through through early Saturday. We do have some steep lapse rates aloft, but thankfully instability is somewhat lacking. Having the ridge in place helps. Really need to have a trigger for convection to be a concern, like being on the edge of the ridge with a shortwave trough or vort max. Therefore, expecting mainly cirrus at this point. Will continue to monitor regardless.

AVIATION

(18Z TAFS) Issued at 1055 AM PDT Wed Aug 5 2026

Seeing most inland terminals returning to VFR conditions late this morning with the remaining soon to follow by 20Z. The exception being KHAF where at least MVFR conditions are expected throughout much of the day. Onshore winds will increase by this afternoon and persist through the early evening before diminishing after sunset. As such, expecting MVFR ceilings to return to the coast and lower to IFR (potentially LIFR) as stratus pushes inland into the interior valleys early Thursday morning. Any stratus and/or fog that does develop will mix out by mid-to-late morning on Thursday.

Vicinity of SFO...VFR. VFR conditions have returned to KSFO at this hour and is likely to prevail through much of the daytime hours with an increase of west to northwest winds through this afternoon and early evening. Expecting an earlier return late this evening around 05Z and linger through at least 18Z Thursday. There is a low-to- moderate confidence for IFR conditions early Thursday morning, yet confidence is not high enough to include in this TAF package, yet have mentioned SCT for the timeframe it has the greatest potential.

SFO Bridge Approach...Later return of stratus Thursday morning, otherwise similar to SFO.

Monterey Bay Terminals...VFR conditions are forecast to return by around 1930Z, KSNS has already scattered out. Onshore winds increase this afternoon before MVFR ceilings return late this evening and lower to IFR a bit later in the evening. There is the potential for LIFR conditions late in the night into Thursday morning, yet again confidence is not high enough to include in this TAF package.

MARINE

(Today through Monday) Issued at 950 AM PDT Wed Aug 5 2026

Light to gentle south to southwesterly breezes will persist through Thursday along with seas between 2-6 feet. Winds will begin to increase again out of the northwest going into Friday with building seas and hazardous conditions for small craft returning for the upcoming weekend.

FIRE WEATHER

Issued at 1000 AM PDT Wed Aug 5 2026

Marine layer brought relief to lower elevations this morning, but above the marine layer another nocturnal drying event bringing single digit RH. Simply put, little to no recovery last night.

Cooler and slightly more humid conditions are expected across the interior today and Thursday. Despite the "cooldown" temperatures across the interior will still be in the 90s to low 100s Wed/Thu with min RH teens. Still expecting an onshore push each afternoon/evening with breezy to gusty winds leading to a few hours of elevated fire weather conditions.

High pressure will build back over the district late Thursday into Friday. As such, the marine layer will become more compressed and interior heat increasing and humidity decreasing. Peak times of greatest concern will be each afternoon/evening Sat/Sun. This will push Energy Release Component (ERC) back up to critical levels. ERC values have climbed above the 97th percentile within the Interior Central Coast and Diablo-Santa Cruz (Diablo Mountains and Santa Cruz Mountains) zones with the Mid Coast to Mendocino Zone (North Bay) to reach the 97th percentile this week. Large fires become more frequent after ERC values cross the 90th percentile with extreme burning conditions expected with ERC values above the 97th percentile. 100 hr fuels continue to respond to the hot and dry conditions with values reaching critical levels across the region. Latest intel also shows Live Fuel samplings are also heading toward critical levels.

Lastly, we're tracking some high level moisture streaming in from the south Friday and over the weekend. As of right now, upper level instability seems limited so high based thunderstorms are not likely. If anything, some high cirrus is possible with some higher dew points.

MM

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.