


Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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938 FXUS66 KMTR 201810 AAA AFDMTR Area Forecast Discussion...UPDATED National Weather Service San Francisco CA 1110 AM PDT Sun Jul 20 2025 ...New AVIATION... .KEY MESSAGES... Updated at 133 PM PDT Sat Jul 19 2025 - Cooling trend begins Monday with a widespread return to below normal temperatures. - Localized elevated fire weather threat for the East Bay Hills Sunday and Monday due to dry conditions and gusty winds. - Gusty winds return late Sunday and continue through Monday along the coast, the higher terrain, and mountain gaps/passes. && .UPDATE... Issued at 914 AM PDT Sun Jul 20 2025 Stratus coverage, while still widespread, is a bit more patchy across the Bay Area than it was yesterday morning. The 12Z OAK sounding shows the marine layer compressed to around 1500 feet overnight which would help explain why the stratus coverage was patchier. Pockets of diminished visibility along the coast have started to improve with further improvement expected as stratus clears by mid to late morning. Gusty winds remain on track to develop this afternoon/evening with the only adjustment to the && .SHORT TERM... Issued at 217 AM PDT Sun Jul 20 2025 (Today and tonight) The forecast for the most part is starting to sound like a broken record: morning stratus layer clearing to the coast by the afternoon with seasonably cool temperatures. While the overall weather picture is the same there are some details that differ: high temps, marine layer depth, and winds. The upper level ridge that brought some inland warmth Saturday has weakened and is being replaced by an upper level trough/lower 500mb heights. The overnight satellite fog product shows the marine layer has better coverage than 24 hours due to the building upper level trough. Have added some coastal drizzle/patchy fog to the forecast given the current marine layer set up. The upper level trough will also help to knock inland temperatures down a few degrees. The biggest weather change for today will be the winds. For several days now we`ve been mentioning increasing winds late Sunday into Monday. Latest guidance continues to advertise a solid push of winds. In fact, onshore gradients (SFO-SAC) are projected to be 4 to 5 mb later this afternoon and evening yielding some robust winds for the East Bay gaps/passes and West Delta region. Borderline for a wind advisory, but gusts in the 30-40 mph with a few isolated up to 50 mph will be possible. It will be windy along the coast, higher terrain, and favored valleys, but not as strong as the East Bay. It goes with out saying, but the uptick in winds will create increased fire weather concerns for the East Bay. While winds increase humidity values are lowering to the 25-40% range. While not critical RH the wind will override it. ERC chart values take a dip today the more wind based index of the Burn Index reaches in the 90th percentile. So that means, flashier fuels and more flammable live fuels could carry fire. Speaking of fire weather concerns a classic nocturnal drying event is taking place over the Santa Lucia range. As stratus rolled through the Salinas Valley rapid drying occurred above it with a sensor on Chews Ridge dipping into the single digit RH. Sunday night into Monday: Solid onshore flow remains with breezy conditions lingering in the East Bay. The marine layer will deepen with more coastal drizzle. && .LONG TERM... Issued at 254 AM PDT Sun Jul 20 2025 (Monday through Saturday) To kick off another work week more of the same - night/morning clouds with afternoon inland sunshine. Onshore winds ease slightly early Monday before ramping back up Monday afternoon/evening favoring the inland gaps/passes. Thereafter pretty benign weather continues into next weekend. Marine layer is locked in with cooler the seasonal temperatures thanks to an anomalously low upper level trough overhead. Some longer range guidance even deepens the trough and has an a cut- off low form over the region by Thursday. Simply put, if you`re enjoying the cooler weather with some afternoon sunshine you`ll enjoy the long term forecast. && .AVIATION... (18Z TAFS) Issued at 1105 AM PDT Sun Jul 20 2025 Largely a persistence forecast for the terminals with VFR anticipated at most sites (except KHAF) this afternoon before MVFR to LIFR stratus returns this evening and into the overnight hours. Confidence in the forecast is medium to high, though there are the usual nuisances due to terrain and offshore eddy formation. KAPC may be the beneficiary of an eddy just east of the GG gap and clearing will be later compared to some of the other terminals. Otherwise, onshore flow will translate to wind gusts near 25 knots at the terminals nearest the SF/San Pablo Bays. Onshore flow tonight into Monday will usher in another round of marine stratus at all terminals. The current KOAK TAF indicates MVFR, as the window for IFR seems to be short-lived and confidence isn`t quite high enough to include, yet. Confidence is high that by 0900 UTC, just about all TAFs will be inundated with stratus. Reduced visibility should be anticipated at KSTS and KHAF due to BR/DZ. With the onshore flow remaining persistent, VFR may not return until 1700 UTC or after at the coastal terminals. Vicinity of SFO...There remains an opportunity for occasional MVFR cigs through 1900 UTC today, but the afternoon will largely be VFR. Wind gusts increase up to around 25 knots by 2100 UTC and persist through the early evening. Some guidance (4 out of 10 models) offer an early onset of MVFR stratus and potential loss of VAPS as early as 0300 UTC. For now, will lean a bit more on climo which supports MVFR around 0600 UTC. If MVFR ceilings do arrive earlier, the evening push may be impacted. Similar to KOAK, the chances for IFR cigs is non-zero, but not high enough to include in the TAF at this time. Impacts to the Monday morning push are highly probable with MVFR lingering through the noontime hour. The current TAF set is a little pessimistic on the back end with MVFR through Monday mid-afternoon, however, trends in satellite and model guidance will be monitored for refinements. SFO Bridge Approach...Satellite and webcam imagery support VAPS and this will likely continue through the afternoon/evening. MVFR will return between 0600-0800 UTC with ILS operations likely warranted through at least late Monday morning. Monterey Bay Terminals...Stratus continue to quickly erode late this morning and VFR should be anticipated through at least 00 UTC. Near or shortly after, MVFR/IFR stratus will return with LIFR cigs by 0600 UTC. A few instances of LIFR at KSNS are expected to transpire just prior to 0600 UTC as flow responses to the diurnal heating/cooling across the region. IFR visibility is also most probable at KMRY as convergence leads to meager lift along the marine/land interface. VFR does not appear likely until after 1700 UTC Monday. && .MARINE... (Today through Friday) Issued at 914 AM PDT Sun Jul 20 2025 Moderate breezes to near-gale force wind gusts are forecast today and into Monday. This will result in hazardous boating conditions for smaller vessels near and across the northern San Francisco and San Pablo Bays. Hazardous boating conditions should also be anticipated across northern outer waters beyond 10 nautical miles from the shore. In addition, northwesterly coastal jets with strong breezes are anticipated this afternoon across northern Monterey Bay and near Point Sur. These strong breezes will persist into the pre-dawn hours on Monday across the Big Sur coastline. Slight to moderate seas persist through the remainder of the forecast period. Winds ease some through Tuesday, except across southern portions of the Big Sur coast, where strong northwesterly breezes persist. Otherwise, reduced visibility should be anticipated during the morning hours due to fog/drizzle. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 9 PM PDT Monday for SF Bay N of Bay Bridge. Small Craft Advisory from 3 PM to 9 PM PDT Monday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory until 9 AM PDT Monday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...MM LONG TERM....MM AVIATION...Bain MARINE...Bain Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea