textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1237 PM PDT Sun Aug 23 2026

- Near to slightly below normal temperatures persist in the marine layer this week

- Warm and dry conditions continue above 1000 feet

SHORT TERM

Issued at 1237 PM PDT Sun Aug 23 2026 (This evening through Monday night)

Not too much change in the forecast today as the Bay Area and Central Coast remain in between an upper level trough to the north and a ridge over the Desert Southwest. Ridging remains more dominant through this evening before the center of the ridge shifts eastward early Monday and troughing becomes more dominant over the region. High temperatures are forecast to peak in the upper 80s to low 90s across the interior with far interior Monterey County reaching the low 100s. Coastal areas are benefiting from a shallow (~1000 foot) marine layer that brought patchy stratus and drizzle to the coast and the SF Bay shoreline. This will keep temperatures cooler in coastal areas with highs peaking in the 60s to low 70s.

Heading into Monday, the center of the upper level ridge will shift eastward with troughing becoming the dominant feature over us. The return of troughing will help the marine layer to (slightly) deepen and bring it from approximately 1000 ft to 1200-1500 ft. A slightly deeper marine layer will allow for a greater inland intrusion of stratus, but, stratus is not likely to be as widespread as it was last week. Temperatures are expected to drop by around 5 degrees for most interior locations. This will see a return of highs in the low to mid 80s while the higher elevations above the marine layer will stay comparatively warmer in the upper 80s to low 90s. Coastal areas will remain in the 60s to low 70s with additional periods of coastal drizzle likely during the early morning hours. The one questionable part of the forecast is if any thunderstorms will be able to develop across the North Bay Interior Mountains (particularly Napa County) early Monday morning. The Euro suggests that there will be sufficient moisture, instability, and lift as a weak shortwave trough moves in to California for orographically driven thunderstorms to develop there early Monday morning. NBM guidance gives around a 5% chance of thunderstorms developing. Any precipitation that falls would likely be virga/evaporate before reaching the surface given model Skew-T soundings showing a large dry layer between the mid and lower levels of the atmosphere. Confidence remains low overall in storm development, however, as other models (GFS, NAM, HRRR, RRFS) do not support storms developing tomorrow morning with the Euro being an outlier.

LONG TERM

Issued at 1237 PM PDT Sun Aug 23 2026 (Tuesday through next Saturday)

Troughing prevails through Tuesday with high temperatures remaining in the 60s to 70s along the coast, 80s across the interior, upper 80s to low 90s across the higher elevations, and upper 90s to low 100s across the interior Central Coast. Stratus is expected along the coast and portions of the SF Bay shoreline but continues to be limited in extent. The center of the upper level ridge shifts back westwards Wednesday to Thursday with high temperatures warming by around 5 degrees across the interior (largely returning temperatures to the upper 80s to 90s). Friday into the weekend, temperatures cool by a few degrees as ridging weakens and troughing deepens/strengthens over the Pacific. Troughing looks to continue into next week with a deep upper level low moving into the Pacific Northwest and Northern California. It will be worth keeping an eye on this incoming trough and the arrival of any potential tropical moisture towards the end of the forecast period. The latest NHC guidance shows three active areas of tropical interest offshore of Mexico with recently named TS Iselle in the vicnity as well. Guidance is starting to indicate some tropical moisture from these systems may be brought north as the trough arrives but it is unclear how far north this tropical moisture will go. Some models keep it more over Southern California while others bring it up into Monterey/San Benito counties. Models are already showing an increase in southerly swell associated with the uptick in tropical activity across the Eastern Pacific this weekend into early next week.

AVIATION

(18Z TAFS) Issued at 1154 AM PDT Sun Aug 23 2026

Widespread VFR conditions prevail through much of the afternoon with gentle to moderate onshore breezes. IFR stratus will linger at HAF into the early afternoon as the mixing of dry air continues along the coast. The marine layer is expected to remain compressed around 1000 to 1200 feet tonight which will limit its inland expansion. High confidence for IFR to LIFR ceilings to develop at the coast with potential reductions to visibility. Medium confidence on STS developing IFR ceilings given the lack of weak offshore winds aloft. Overall, the wind flow above the marine layer will remain onshore through the TAF period. Despite this, medium confidence on whether APC will develop a ceiling given the shallow marine layer.

Vicinity of SFO...VFR through the day with onshore winds settling in this afternoon. Medium confidence on low-end MVFR ceilings developing at the terminals early Monday morning. Given the prominent onshore flow and shallow marine layer, a later stratus arrival is anticipated (09-12Z Monday). VFR conditions should prevail by late Monday morning.

SFO Bridge Approach...Cloud cover overnight may be patchy over the San Mateo bridge as stratus coverage is not expected to travel far south into the Santa Clara valley. Otherwise, similar to SFO.

Monterey Bay Terminals...Northwest winds prevail at SNS through the TAF period meanwhile MRY remains more west to southwest. Gentle to moderate winds increase through the afternoon before easing and becoming variable overnight. Medium confidence for an earlier onset of stratus this evening around sunset with IFR-LIFR ceilings. Reductions to visibility due to mist are possible overnight with the compressed marine layer.

MARINE

(Today through Friday) Issued at 920 AM PDT Sun Aug 23 2026

Northwest winds remain moderate through Sunday and gradually ease to gentle breezes through the middle of next week before increasing again. The northern outer waters will continue to experience near gale force gusts into the evening. Wind driven seas remain slight to moderate entering the work week. Reduced visibility due to smoke from the Timber Fire is expected along the Big Sur coast as the marine inversion holds through the morning.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt Reyes 10-60 NM.