, Issued at 1206 AM PDT Sun Aug 9 2026 (Today and tonight)
The 00Z balloon observed a 925 mb temperature of 30.35 degrees Celsius (third hottest for the date and time), 850 mb temperature of 28.75 degrees Celsius (second hottest for the date and time), and 500 mb height of 5970 meters (record for the date and time). Satellite shows stratus clearing off the coast due to a strengthening ACV-SFO surface pressure gradient. Northerly/offshore flow down the Northern Sacramento Valley Sunday morning will help push the marine layer back to the coast. Both of these factors should support Sunday being the hottest day of this event; however, if the marine layer prevails and northerly/offshore winds don't develop we could have a repeat of Saturday with our forecast being too hot for the lower elevations. Nonetheless, temperatures will be 10 to 15 degrees above normal outside of the marine layer influence with widespread moderate HeatRisk and areas of major HeatRisk in the higher terrain. 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. Have opted to leave the Pacific Coast out as it would be marginal and overnight if it occurred; however, high tide may cutoff access to some beaches.
..issued at 1206 AM PDT Sun Aug 9 2026 (Monday through Saturday)
Cooling trend kicks off Monday as upper-level shortwave troughing develops off the West Coast. This will moderate temperatures to near normal, deepen the marine layer bringing a chance for drizzle, and increase onshore flow. A reinforcing trough Wednesday will bring more prominent troughing off the West Coast Thursday and into the weekend. This along with a resurgence in monsoonal moisture may be enough to bring elevated rain showers/thunderstorms to the forecast. While there's no mention in the official forecast now, it may be warranted as we get closer.
(12z TAFS) Issued at 523 AM PDT Sun Aug 9 2026
A narrow channel of coastal stratus, fog and mist /MVFR-IFR-LIFR/ have held together and remains trapped beneath a strong lower level temperature inversion associated with a strong 500 mb high pressure system. Part of this stratus, fog and mist has reached into the Bay Area and the north Central Coast. The marine layer depth is approx 1000 feet.
Satellite shows an area of clear sky out over the outer waters and offshore waters which corresponds to an area of warmer air, primarily drifting southward. Satellite also shows stratus and fog redeveloping to our north. The leading edge of this stratus may join the nearly stationary stratus south of Point Arena during and just after daybreak. This pattern is characterized by large temperature differences over short distances, mainly in the vertical and also from the coastline to inland valleys (sharply warmer aloft, at the August maximum otherwise not atypical of either July or August). It's noteworthy that air temperatures in the lower level temperature inversion are in the 80s and lower 90s. With the wind flow weighted to onshore, we're essentially in a persistence forecast. Diurnal surface warming will tap the lower level temperature inversion warmth, vertical mixing and warming will mix out the stratus, fog and mist to VFR back to the coastline today. The gradient of surface pressure remains weighted to some northerly (ACV-SFO) otherwise onshore per NAM output showing 4 mb to almost 5 mb SFO-SAC during the afternoon and evening.
Depending how well (or not) the coastal stratus to our north holds together during mixing today will determine if coastal stratus, fog and mist return tonight and Monday morning. The NAM has been verifying a little better than the HRRR model on this forecast. The NAM leans toward stratus, fog and mist returning tonight and Monday morning.
Recent GFS/NAM/HRRR output has also showed mid level instability arriving from southern California approx Monday timeframe, but it appears to dissipate while running northward into the strong ridge and mid level dry air just to our north.
Vicinity of SFO, Stratus /IFR/ forecast mix out time is 17z today. VFR for the remainder of the day then stratus is forecast to return 10z Monday. West to northwest wind 5 to 15 knots except 15 to 25 knots this afternoon and evening.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Stratus, fog and mist /IFR-LIFR/ mixing out to MVFR-VFR by late morning. Stratus, fog and mist /IFR-LIFR/ returns tonight and Monday morning. Mainly west to northwest winds 5 to 15 knots.
(today through Friday) Issued at 436 AM PDT Sun Aug 9 2026
Fresh to strong northwest winds persist with moderate seas building to rough seas up to 12 feet today, lasting through mid week. Northern coastal waters will be hazardous for small craft with occasional near gale force gusts possible through early week. The San Francisco Bay north of the Bay Bridge into the Delta will have gusty onshore winds through late evening. Long period southerly swells at around 15 to 17 seconds are still present in the coastal waters.
Ca, Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506- 508-529-530.
Heat Advisory until 10 PM PDT this evening 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 this morning to 3 AM PDT Monday for Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory until 9 PM PDT Monday for Pt Arena to Pt Reyes 10-60 NM.
