textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1206 AM PDT Sat Aug 8 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 through Thursday morning

SHORT TERM

Issued at 1206 AM PDT Sat Aug 8 2026 (Today through Sunday)

Upper-level ridging across the Four Corners will expand westward Saturday bringing widespread moderate to areas of major HeatRisk to the interior over the weekend. This will support temperatures 10-15 degrees above normal and a compressed marine layer. While messaging remains the same, the ridge is forecast to be slower to break down with northerly/offshore flow developing at 925 mb down the Northern Sacramento Valley on Sunday. This will make Sunday the hottest of the two days in some locations, namely the North Bay Interior Valleys, San Francisco Bayshore, and San Francisco. Have opted to leave them out of the Heat Advisory still; however, they may need to be included in subsequent forecasts. 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 through Thursday morning. The Pacific Coast may need to be added Sunday through Tuesday. Tonight's forecast was overdone by 0.1 ft and while that is not a lot, it is the difference of whether or not the Pacific Coast gets included. We will wait to see how our forecast performs and what the trend is after Saturday night's high tide before we make a decision one way or the other.

LONG TERM

Issued at 1206 AM PDT Sat Aug 8 2026 (Monday through Friday)

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. Even with the cooling trend and the deepening of the marine layer, the increase in onshore wind will support elevated fire weather conditions into next week. The upper-level pattern along with a resurgence in monsoonal moisture may be enough to bring elevated rain showers/thunderstorms to the forecast as early as Thursday and into next weekend. Whether or not the aforementioned trough pinches off to become a low or not will be important for the lifting mechanism factor. As far as instability and moisture go, conditionally unstable lapse rates and sufficient MUCAPE will overlap with PWAT values in excess of an inch. While there's no mention in the official forecast now, it may be warranted as we get closer.

AVIATION

(12Z TAFS) Issued at 505 AM PDT Sat Aug 8 2026

A strong 500 mb high pressure system and large scale compression continue to slowly decrease the marine layer depth. At the same time, satellite shows widespread stratus and fog over the coastal and offshore waters with onshore winds transporting stratus, fog and mist /MVFR-IFR-LIFR/ inland underneath the high and across low lying areas of the Bay Area and north Central Coast. Otherwise it is VFR. In the marine layer temperature inversion across the hills and mountains it's much warmer and dry. The SFO-SAC pressure gradient is 3.0 mb and it is forecast to reach near 4 mb this afternoon. Stratus and fog have a solid start, however diurnal surface warming will connect with the lower level temperature inversion and raise the temperatures and mix out the stratus and fog to the coastline.

Recent high resolution model output has been showing drier northwest winds arriving later today, tonight and Sunday eroding the coastal stratus north-south, perhaps leaving a narrow channel of stratus and fog /IFR-LIFR/ along the immediate coastline along with an inland intrusion possible tonight and Sunday morning. The high resolution rapid refresh model leans less stratus and fog and the NAM leans more stratus and fog remaining; 12-24 hours from now it's a low confidence forecast.

Vicinity of SFO...Stratus /IFR/ until 17z today then VFR. Stratus /IFR/ is forecast 10z Sunday. West to northwest wind 5 to 15 knots except 15 to 25 knots from late morning through mid evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus, patchy fog and mist /IFR-LIFR/ lifts to MVFR-VFR by late morning. Stratus, patchy fog and mist /IFR-LIFR/ return tonight and Sunday morning. West to northwest winds 5 to 15 knots.

MARINE

(Today through Thursday) Issued at 426 AM PDT Sat Aug 8 2026

Northwest winds will increase to fresh to strong across the coastal waters with seas in the northern waters becoming hazardous to small craft beginning today and lasting to the middle of next week. Occasional gale force gusts are possible across the outer northern coastal waters. Expect gusty onshore winds across the San Francisco Bay north of the Bay Bridge to the Delta today and Sunday. A long period southerly swell at 15 to 17 seconds persists through the weekend.

FIRE WEATHER

Issued at 1206 AM PDT Sat Aug 8 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. Elevated fire weather conditions are expected into next week as onshore flow increases on the heels of the near-critical hot and dry event this weekend. The upper-level pattern along with a resurgence in monsoonal moisture may be enough to bring elevated rain showers/thunderstorms to the forecast as early as Thursday and into next weekend.

Sarment

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506- 508-529-530.

Heat Advisory from 10 AM this morning to 10 PM PDT Sunday for CAZ503-504-510-512>518.

PZ...Small Craft Advisory from 9 AM this morning to 9 PM PDT this evening for SF Bay N of Bay Bridge.

Small Craft Advisory from 9 AM to 9 PM PDT Sunday for Pt Arena to Pt Reyes 0-10 nm-SF Bay N of Bay Bridge.

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