083 FXUS66 KMTR 271139 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 439 AM PDT Sun Jul 27 2025 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 1209 AM PDT Sun Jul 27 2025 - Temperatures warm slightly while remaining below seasonal normal through the week. - Strong onshore afternoon winds will gradually increase through mid-week. && .SHORT TERM... Issued at 1209 AM PDT Sun Jul 27 2025 (Today and tonight) The marine layer has compressed to around 1,600 feet according to the 00Z sounding, although the Ft. Ord profiler has indicated some expansion since then. The current stratus deck is fairly similar to 24 hours ago, with slightly less inland extent. The cloud ceilings are generally below 1,000 feet and falling, which could help bring another round of early morning drizzle to the typical locations. The basic 500 mb pattern is troughing offshore, extending from low pressure in the Gulf of Alaska, and high pressure over the Gulf States. California is centered between these two synoptic features. The high pressure will nudge the trough a little today. This will cause the 850 mb temperature to rise and max temperatures are expected to climb anywhere from 2-5 degrees compared to yesterday. Otherwise it will be pretty similar with morning clouds, a clear breezy afternoon, and clouds returning in the evening. Despite the modest warming, we are still expected to stay below the seasonal normal. && .LONG TERM... Issued at 1209 AM PDT Sun Jul 27 2025 (Monday through Saturday) The pattern described above is pretty stable, though there is a gradual long term trend. The Gulf of Alaska is a well known storm graveyard, and the 500 mb low there will gradually fill over the next several days. Meanwhile the subtropical high over the Gulf States will gain strength and push west. This feature will eventually extend a ridge from Texas to eastern Washington. At the surface this evolution will lead to a gradual increase in the N-S pressure gradient between subtropical high pressure offshore and a thermal low over Arizona. The Eureka to Santa Barbra gradient is currently around 1 mb and will reach 6 or 7 mb by mid week. Meanwhile the E-W gradient will remain fairly steady. The SFO-SAC and SFO-WMC gradients remain positive and diurnally driven according to a confident 2 km WRF ensemble. All these means that winds will remain onshore (good for fire weather) while the strength increases through the next several days. The 850 mb temperature will also gradually increase from around the 25th percentile today to around 75th percentile by Wednesday. This will translate to a very slight warming trend, however the onshore wind will be the primary driver, and keep most areas slightly cooler than normal. Higher elevations will feel the warmer and drier air mass, however. Regarding fire weather, all regions are enjoying fuel moisture well above normal, but the forecast is for the trend to reverse starting Monday, especially above the marine layer. && .AVIATION... (12Z TAFS) Issued at 437 AM PDT Sun Jul 27 2025 Currently a mixed bag of LIFR-MVFR at the terminals. Interior terminals will likely improve to VFR by this afternoon with stratus sticking close to the coast - potentially impacting bayshore and coastal terminals through the TAF period. Vicinity of SFO...Currently IFR with westerly flow. If VFR is achieved, it will likely be brief with high confidence in a return of an IFR ceiling tonight. Westerly flow will prevail through the TAF period. SFO Bridge Approach...Low stratus clouds will likely linger between OAK, SFO, and northward with a 20% chance that OAK and SFO will not achieve VFR. Monterey Bay Terminals...Currently IFR with southwesterly flow at MRY and IFR with westerly flow at SNS. Brief VFR may be achieved this afternoon, but low stratus will stick close to the coast with high confidence in a return of IFR ceilings tonight. Westerly winds will prevail through the TAF period. && .MARINE... (Today through Friday) Issued at 437 AM PDT Sun Jul 27 2025 Moderate to fresh northwesterly breezes will prevail with widespread strong gusts expected by tomorrow afternoon. Moderate to rough seas and low clouds with drizzle will prevail through Thursday. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm. Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Monday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 AM to 9 AM PDT Monday for Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...Sarment MARINE...Sarment 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