textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1211 AM PDT Fri Aug 7 2026

- Warming trend through the weekend will result in moderate to major HeatRisk for the interior

- Near-critical fire weather conditions in the higher terrain through Sunday

- Minor coastal flooding for bayshore locations along the San Francisco Bay, San Pablo Bay, and Monterey Bay Friday evening through Thursday morning

UPDATE

Issued at 950 AM PDT Fri Aug 7 2026

No major updates to the ongoing forecast for today. Planning to add the Southern Salinas Valley to the Heat Advisory 10 AM Saturday through 10 PM Sunday. Otherwise, stratus is retreating to the coast as of this morning and will give way to mostly sunny sky conditions across the interior. However, passing high clouds are present as mid/upper level moisture wraps around the high over the Desert Southwest.

RGass

SHORT TERM

Issued at 1211 AM PDT Fri Aug 7 2026 (Friday through Sunday)

Upper-level ridging across the Four Corners will expand westward Friday. Areas of moderate HeatRisk across the interior on Friday will expand to become widespread on Saturday and Sunday with areas of major HeatRisk. Saturday and Sunday will be the hottest days of the week with temperatures 10-15 degrees above normal. Subsidence aloft will compress the 1,000 foot marine layer, keeping relief confined to the immediate coast. Near-critical fire weather conditions persist through the weekend across the interior due to very hot and dry conditions. Minor coastal flooding is expected during the highest high tide (evening/overnight) for bayshore locations along the San Francisco Bay, San Pablo Bay, and Monterey Bay Friday evening through Thursday morning. The Pacific Coast may need to be added Sunday through Tuesday, it will depend on how the positive anomaly performs leading up to it.

LONG TERM

Issued at 1211 AM PDT Fri Aug 7 2026 (Monday through Thursday)

Global ensemble clusters are in agreement that upper-level shortwave troughing will develop Monday off the West Coast between subtropical high pressure across the Eastern Pacific Ocean and the Four Corners high. This will result in temperatures moderating to near normal and the return of a marine layer around 1,000 feet. The surface pressure gradient will support northerly winds across the waters that will be hazardous to small craft.

AVIATION

(12Z TAFS) Issued at 520 AM PDT Fri Aug 7 2026

Mid and high clouds are moving northward over the forecast area and there may be a few high based light showers/virga based on KMUX data. Strong 500 mb high pressure continues and the lower level temperature inversion prevails in the hills and mountains. At the same time, the marine layer is well established with a cool air intrusion on northwest winds along the coastline and into the nearby coastal valleys. The SFO-SAC pressure gradient is 2.9 mb, 1 mb greater than 24 hours ago, a decent onshore gradient for 5 am.

At the moment the overall pattern is stable and not likely to become disrupted. Even though mid and high clouds are present and slowing radiative cooling, cool air advection is taking place within the marine layer, supporting stratus, fog and mist /MVFR- IFR-LIFR/. It's favorable thermodynamic conditions e.g. at the air/sea interface for stratus and fog and btw, kudos to the NAM 1000 mb forecasts for helping to quickly identify (and observations to verify) this shallow cool air intrusion. Cloud ceilings have lowered to IFR-LIFR during the overnight hours because of favorable air/sea conditions and a slight decrease in the marine layer depth.

This complex cloud pattern mix will carry through morning, the question is how long will it take to mix out the stratus, fog and mist under August sun angle surface heating? Some delay in surface heating means potential delay for stratus, fog and mist to mix out to VFR. Interestingly, weak thermal troughing is located at the 500 mb level today and is slow to move northward out of the forecast area. Timing mix out is a low confidence forecast, with uncertainty will go with late morning mix out, but it may also take another couple hours to fully mix out along the coastline. The NAM forecasts upwards of 4 mb SFO-SAC pressure gradient in the afternoon. So far the marine layer has essentially been deeper compared to model forecasts. Satellite shows widespread stratus and fog over the coastal and offshore waters. With onshore winds dominating, expect stratus, fog and mist /MVFR-IFR-LIFR/ to return inland tonight and Saturday morning.

Vicinity of SFO...Stratus /IFR/ until 18z today, but caveat is the current combination of onshore winds, a cooler air intrusion, mid and high clouds may end up slowing mix out to VFR by another hour or two today. Stratus /IFR/ is forecast to return mid evening and continue tonight and Saturday morning. West to northwest wind 5 to 15 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus /IFR-LIFR/ improving to MVFR by late morning. The surface cool air intrusion affecting vicinity KSFO, KOAK, KHAF and areas southward along the coast is still arriving here at this hour. While mid and high clouds are drifting overhead, this will at least temporarily slow diurnal warming while the cooler air undercuts the lower level temperature inversion. Caveat, here too it may take another couple hours for stratus /IFR-LIFR/ to lift to MVFR-VFR which may turn out to be by early afternoon. West to northwest winds 5 to 15 knots.

MARINE

(Today through Wednesday) Issued at 950 AM PDT Fri Aug 7 2026

Moderate northwest winds continue on a gradual increase towards fresh to strong breezes with moderate seas building to rough by Sunday. These conditions remain elevated through the middle of next week, particularly across the northern outer waters. A long period southerly swell around 15 to 17 seconds persists through Monday.

FIRE WEATHER

Issued at 1211 AM PDT Fri Aug 7 2026

Near-critical fire weather conditions persist through the weekend across the interior due to very hot and dry conditions. Strong thermal belting, extended burn periods, elevated PIG, and near or record BI/ERC values are expected. Temperatures will be 10 to 15 degrees above normal with a compressed marine layer. Poor minimum daytime relative humidity as low as 10% in the afternoons with little-to-no recovery overnight is expected with nocturnal drying in the highest terrain. Even with critically dry conditions, wind is the limiting factor preventing this from being a Fire Weather Watch/Red Flag Warning event. Outside of the diurnal sea breeze that will bring breezy conditions in the afternoons and evenings through gaps and passes, onshore flow will be light. Additionally, critical conditions are not expected to meet coverage or duration requirements to warrant a product.

Sarment

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory from 5 PM this afternoon to 2 AM PDT Thursday for CAZ006-506-508-529-530.

Heat Advisory from 10 AM Saturday to 10 PM PDT Sunday for CAZ503- 504-510-512>515-517-518.

PZ...Small Craft Advisory from 3 PM to 9 PM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM.