Issued at 904 PM PDT Thu Jul 3 2025
Taking a quick look at various observations this evening and things look to be on tap. Stratus is forming along the San Mateo and Monterey coasts and slowly while breezy onshore flow is being observed, especially over the portions of the Diablo Range.
, Issued at 135 PM PDT Thu Jul 3 2025 (This evening through Friday)
The forecast is on track early this afternoon with onshore flow continuing this afternoon. The SFO-SAC MSLP "gradient" continues to increase as diabatic heating induces surface pressure falls across the Central Valley. In addition, larger scale synoptic scale forcing in the form of an upper trough continues to encourage onshore flow. In response, areas across the East Bay, the San Bruno Gap and Salinas Valley are experiencing wind gusts averaging between 25 mph and 45 mph. Short term hi-res guidance such as the 2km PG&E WRF along with our in house WRF indicate that gusts as great as 55 mph are still within the realm possibility this afternoon. We'll continue to advertise an elevated to near- critical fire weather threat across the area this afternoon as a few sites have seen RH fall down to near or below 15%. The isolated nature of these "dry" sites precludes a Red Flag Warning, however, we'll continue to advertise/promote fire safety via partner discussions as well as via our web page and social media.
Winds will continue through the evening hours and the airmass across some of the elevated regions of the East Bay will likely not decouple. This will translate to winds remaining elevated. The 12Z OAK RAOB showed the moist layer beneath the inversion (the marine layer) was around 1200 ft AGL. Forecast cross-sections show the marine layer compressing further to around 1000 ft AGL in the wake of the aforementioned upper trough (slight shortwave ridging). This will translate to overnight RH recovery below 50% for the higher terrain across parts of the Santa Cruz Mountains, the Diablo and Santa Lucia Ranges.
With the loss of the upper trough, onshore flow and an approaching diffuse frontal boundary (albeit weakening) may loosen up the surface gradient some on Friday. In fact the PG&E WRF, the MTRWRF and higher-end NBM probabilities indicate reduced flow as a whole during the afternoon hours. While the lack of upper support may take the edge off of the wind, the Central Valley will still warm up quickly. This should continue to drive an MSLP difference and thus diurnal onshore breezes. There will remain an enhancement of the wind field across gaps, passes, and valleys with gusts still as great as 45 to 50 mph. Afternoon RH will still dip down between 15 and 25 percent, and that'll necessitate another round of an elevated to near critical fire weather threat. This will be particularly true, given the potential for additional ignitions given the holiday weekend. Please be mindful of your outdoor activities and obey any local burn/fire restrictions.
..issued at 135 PM PDT Thu Jul 3 2025 (Friday night through next Wednesday)
Not to sound like a broken record, but please be mindful of your outdoor activities and obey any local burn/fire restrictions on Friday evening given the dry grasses and brush.
With winds offshore abating some, we'll likely see upwelling of colder Pacific Ocean waters setting the stage for the development of a thick deck of marine layer stratus. The diurnal pressure gradient should support advection of the marine stratus into the coastal regions this weekend. The marine layer is forecast to thicken some up to around 1500 ft this weekend which fits our climatological pattern ("No Sky July"), particularly along the coast. The Extreme Forecast Index (from the EFI) suggests that the EPS mean forecast is cooler than the model climate along the coast and this increases confidence in a marine layer intrusion. NBM temperatures seem reasonable, but we may need to make some alterations to MaxTs on Saturday and Sunday.
Next week will be characterize by a gradual warming trend. The global guidance indicates that the progression of the ridge will be impeded by a developing cutoff upper trough that spawning from the zonal flow across the Pacific Northwest. Both the 12Z GFS/ECMWF advertise this feature in addition to the 00Z Cluster Analysis through at least the middle of next week. This translates to predominantly onshore flow until the SW US ridge attempts to build. When/how that happens yields a high degree of forecast uncertainty. EFI also seemed a bit underwhelming (and quite negative) for MaxT/MinT through next week, though this is likely biased by the cooler conditions along the coast. Examining the 850mb temperatures with respect to the SPC Sounding Climatology at Oakland and Vandenberg and forecast mean values would place them roughly around the 75th percentile for both areas. The 850mb temperature forecast exhibited a high degree of spread (especially in the GFS ensemble), so there's still an opportunity for things to be warmer or colder than forecast. What does appear most certain is that the warmest locations (perhaps with isolated pockets of 'Moderate' HeatRisk) across the Bay Area and Central Coast Wednesday onward will be across the southern Salinas Valley, as well as across interior sections of the North Bay, East Bay, and South Bay. Stay tuned for details.
(06z TAFS) Issued at 1005 PM PDT Thu Jul 3 2025
IFR and MVFR CIGS are building along the coast along with mist and drizzle and are affecting HAF as well as the Monterey Bay terminals. Winds reduce across the region into the evening and CIGs look to fall further into the night. Moments of low clouds also look to affect OAK and the North Bay terminals later into Thursday morning. Inland clearing begins in the mid morning with most TAF sites going VFR before the midday. The exception will be HAF, which keeps CIGs through the TAF period. Winds look to stay light to moderate through the morning and increase into Thursday afternoon, with gusty winds expected around the SF Bay. Expect winds to reduce into Thursday evening but remain breezy around the SF BAY. CIGs begin to move inland from the coast into the late evening, affecting the Monterey Bay terminals and then OAK later that night.
Vicinity of SFO, VFR through the TAF period. Breezy to gusty winds reduce into early night, becoming moderate. Breezy west winds return into the late morning on Thursday with stronger winds and around 31 kt gusts expected in the mid afternoon and through much of the evening. These winds reduce in the late evening but look to stay breezy through that night.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, IFR CIGs look to turn to LIFR later into the night with some pockets of mist and drizzle in the area. Winds become moderate into mid to late Friday morning CIGs erode over the terminals, but expect cloud cover to linger over the Monterey Bay itself. Cloud cover beings to push inland as winds reduce into Friday evening with IFR CIGs filling over the terminals.
(tonight through next Wednesday) Issued at 555 PM PDT Thu Jul 3 2025
Fresh to strong northwesterly breezes and rough seas will continue into Friday. Gale force gusts will be likely across northern waters and near Pt. Sur through Thursday night. Winds easing by early next week. A low-amplitude long period southerly swell will persist through Friday.
Ca, None. PZ, Small Craft Advisory from 9 AM Friday to 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 0-10 nm-SF Bay N of Bay Bridge.
Small Craft Advisory from 9 AM to 9 PM PDT Friday for Mry Bay.
Small Craft Advisory until 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.
Gale Warning until 3 AM PDT Saturday for Pt Pinos to Pt Piedras Blancas 0-10 nm.
