A frontal boundary will bring scattered showers and storms to portions of the Central and Eastern U.S. through the end of the week. Meanwhile, dangerous heat will intensify across the Intermountain West and expand into the Central U.S. by early next week. Elevated wildfire conditions will develop across portions of the Northern/Central Plains and air quality issues will persist in the Northwest. Read More >
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669 FXUS66 KMTR 060454 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 954 PM PDT Wed Aug 5 2026 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 2 PM PDT Wed Aug 5 2026 - Elevated fire weather threat across the interior North and East Bays, and the Diablo and Santa Lucia ranges through midweek. - Widespread Moderate and areas of Major HeatRisk returns for the end of the work week. - Critical fire weather conditions develop Friday and Saturday. && .SHORT TERM... Issued at 200 PM PDT Wed Aug 5 2026 (This evening through Thursday night) While not as extreme as yesterday, today`s 24 hour trend still indicates a downward trend of an additional 2 to 10 degrees. Persistent onshore flow and lurking marine layer led to additional cooling observed today. A welcomed relief for the interior to get a break before the next round of heat. Tonight through Thursday night: Despite high pressure overhead the marine layer will continue to be the main driver of overall weather in the Bay Area and Central Coast broadly speaking. Clouds will move inland at night and clear back to the coast in the afternoon. Greatest impact of the marine layer will be near the coast/bays and lower elevations. Thermal belts remain active with the hills remains mild and dry through the short term. Thursday will once again feature a broad range of temps from the coast to the interior. Onshore flow will also bring some breezy winds each afternoon/evening. Additionally, some high level smoke may lead to some haze. && .LONG TERM... Issued at 230 PM PDT Wed Aug 5 2026 (Friday through next Tuesday) No significant changes for Friday through the weekend from previous forecast. The upper level ridge will flex again over the region bringing higher 500mb heights and even warmer 850mb temps. As a result of the large synoptic set up we`ll see the following in response: compression of the marine layer, increase of temperatures through Saturday and then moderating on Sunday, increasing HeatRisk values to include Major, decreasing RH, and enhancement of the thermal belts. Less confident for a Heat Advisory across the interior on Friday, but very confident we`ll need a Heat Advisory on Saturday. It`s also possible that we may need one on Sunday as well since heat impacts are cumulative and we`ll be day three of the warm up. Starting to sound like a broken record at this point, but the onshore flow/marine layer will keep the natural AC at the coast/bays. We`ll see above normal temps, just not to critical levels. The upper level ridge eases its grip by Monday/Tuesday with subtle cooling as the heat shifts back toward the Central Valley. One other item of note for the long term will be the influx of upper level moisture. Guidance still shows a solid push of high PWAT air from SoCal. The leading edge will nose in as early as Thursday, but the bulk of it will arrive Thursday night through through early Saturday. We do have some steep lapse rates aloft, but thankfully instability is somewhat lacking. Having the ridge in place helps. Really need to have a trigger for convection to be a concern, like being on the edge of the ridge with a shortwave trough or vort max. Therefore, expecting mainly cirrus at this point. Will continue to monitor regardless. && .AVIATION... (06Z TAFS) Issued at 953 PM PDT Wed Aug 5 2026 VFR prevails early tonight with only KHAF and KSNS with MVFR ceilings thus far. The stratus push inland isn`t as dramatic as thought just three hours ago, but confidence remains high that it will eventually spread over most of our area below 1500ft by sunrise Thursday. With high pressure continuing to build, expect VFR conditions by late morning for most terminals, possibly early afternoon for the Monterey Bay sites as a compressed marine layer retreats back to the coast. Vicinity of SFO...Stratus lingering in vicinity of the terminals but currently slow to make much more progress. The inland push isn`t taking hold as quickly as though just a few hours ago, but confidence is high that IFR/LIFR ceilings will develop after midnight and persist through late morning. VFR through the remainder of the forecast period once stratus retreats back to the coast. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...MVFR ceilings will become IFR/LIFR after midnight and continue through late morning at KSNS, possibly early afternoon for KMRY. Moderate to high confidence that IFR/LIFR ceilings return by early evening before sunset with VFR most of the afternoon on Thursday. && .MARINE... (Tonight through next Tuesday) Issued at 953 PM PDT Wed Aug 5 2026 Light to gentle breezes will continue through Thursday with seas between 2-6ft. Northwest winds begin to increase Friday into the weekend with building seas and hazardous conditions for small craft. A long period southwesterly swell of 15-17sec begins on Saturday, peaks on Sunday then begins to subside by the beginning of next week. && .FIRE WEATHER... Issued at 1000 AM PDT Wed Aug 5 2026 Marine layer brought relief to lower elevations this morning, but above the marine layer another nocturnal drying event bringing single digit RH. Simply put, little to no recovery last night. Cooler and slightly more humid conditions are expected across the interior today and Thursday. Despite the "cooldown" temperatures across the interior will still be in the 90s to low 100s Wed/Thu with min RH teens. Still expecting an onshore push each afternoon/evening with breezy to gusty winds leading to a few hours of elevated fire weather conditions. High pressure will build back over the district late Thursday into Friday. As such, the marine layer will become more compressed and interior heat increasing and humidity decreasing. Peak times of greatest concern will be each afternoon/evening Sat/Sun. This will push Energy Release Component (ERC) back up to critical levels. ERC values have climbed above the 97th percentile within the Interior Central Coast and Diablo-Santa Cruz (Diablo Mountains and Santa Cruz Mountains) zones with the Mid Coast to Mendocino Zone (North Bay) to reach the 97th percentile this week. Large fires become more frequent after ERC values cross the 90th percentile with extreme burning conditions expected with ERC values above the 97th percentile. 100 hr fuels continue to respond to the hot and dry conditions with values reaching critical levels across the region. Latest intel also shows Live Fuel samplings are also heading toward critical levels. Lastly, we`re tracking some high level moisture streaming in from the south Friday and over the weekend. As of right now, upper level instability seems limited so high based thunderstorms are not likely. If anything, some high cirrus is possible with some higher dew points. MM && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...MM LONG TERM....MM AVIATION...JM MARINE...JM 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 |
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