A series of fronts will focus locally heavy showers and storms across portions of the central and eastern U.S. through the end of the workweek. Dangerous to extreme heat continues across the Southwest U.S., eventually spreading eastward over the weekend into early next week. Elevated fire weather conditions continue across the Great Basin, with degraded air quality lingering across the Northwest. Read More >
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265 FXUS66 KMTR 051756 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1056 AM PDT Wed Aug 5 2026 ...New AVIATION... .KEY MESSAGES... Updated at 1148 PM PDT Tue Aug 4 2026 - Elevated fire weather threat across the interior North and East Bays, and the Diablo and Santa Lucia ranges through midweek. - Widespread Moderate HeatRisk returns for the end of the work week. - Critical fire weather conditions develop Friday and Saturday. && .UPDATE... Issued at 950 AM PDT Wed Aug 5 2026 Solid marine layer this morning impacting the Bay Area and Central Coast. As another forecaster in the office pointed out this morning pretty impressive to see an over performing marine layer deepen to nearly 1800 feet with anomalously high 500mb heights. Not as much drizzle being reported this morning, but the ample moisture in the low levels has led to mist. Above the marine layer is a completely different story. High elevation sensors showed another classic nocturnal drying event this morning. Sensors showed humidity "recovery" to around 30 percent yesterday evening then humidity values plummeted through sunrise as the marine layer moved inland. This would definitely be a fire weather concern, but fortunately winds are relatively light. Other item of note this morning is some high level smoke being picked up by satellite lurking over the coastal waters and potentially the North Bay. Surface sensors are not showing it reaching the ground as of now therefore it`s likely high level drift smoke. For today - the over performing marine layer is bringing much needed relief to the interior. No Heat Advisories are needed as temperatures cool and HeatRisk concerns decreases. The marine layer will slowly ease back to the coast, but linger for the day. No update needed this morning. Will be focusing on another round of heat later in the week and developing near critical fire weather conditions. MM && .SHORT TERM... Issued at 1148 PM PDT Tue Aug 4 2026 (Tonight through Thursday) The picture from space this evening shows stratus snaking through the the region. Earlier model guidance struggled with the onset of its arrival and to some extent the depth as well. It`s currently around 1000ft and has the potential to get to 1200ft, with coastal drizzle and patchy fog possible tonight and into Wednesday morning. The good news is that this will cool temperatures overnight and perhaps take a bit longer to retreat to the coast Wednesday morning. With ridging not as strong and those factors in place, the threat for Moderate HeatRisk has been pulled back with only a few pockets found across the interior Central Coast and interior E and S Bay regions. Some of those pockets include areas above the marine layer, where temperature recovery won`t be as great. Like the prior shift, will not be issuing a Heat Advisory for Wednesday. Wednesday night into Thursday morning, the forecast will be on repeat. Look for the marine layer and associated stratus to seep into the region leading to another cloudy night. && .LONG TERM... Issued at 1148 PM PDT Tue Aug 4 2026 (Thursday night through next Tuesday) The ridge starts to build back into the region on Thursday, which will compress the marine layer to perhaps 500ft for the next few days. At the surface, winds will have shifted from the south to a more north/northwesterly flow; however, aloft, guidance shows the southerly flow holding. Deterministic models and ensembles show a slug on moisture pushing into our region Thurday-Saturday giving us PWATs ranging from 0.75-1.0, which could lead to things feeling humid. In terms of the heat portion of the forecast, it looks to be on track. Data continues to signal 850mb temps in the 28-30C range, leading to toastier daytime and overnight temperatures. Highs, especially for interior areas and those not affected by the marine layer, will be in the 90s to low 100s while low temperatures there fall into the upper 60s-70s. Widespread Moderate HeatRisk is expected, with some pockets of Major HeatRisk on Saturday. Sunday and Monday, the upper level pattern shows the ridge flattening some. The latest NBM seems to keep temperatures a tad warmer on Sunday, with the more notable interior cooling trend occuring on Monday and Tuesday. && .AVIATION... (18Z TAFS) Issued at 1055 AM PDT Wed Aug 5 2026 Seeing most inland terminals returning to VFR conditions late this morning with the remaining soon to follow by 20Z. The exception being KHAF where at least MVFR conditions are expected throughout much of the day. Onshore winds will increase by this afternoon and persist through the early evening before diminishing after sunset. As such, expecting MVFR ceilings to return to the coast and lower to IFR (potentially LIFR) as stratus pushes inland into the interior valleys early Thursday morning. Any stratus and/or fog that does develop will mix out by mid-to-late morning on Thursday. Vicinity of SFO...VFR. VFR conditions have returned to KSFO at this hour and is likely to prevail through much of the daytime hours with an increase of west to northwest winds through this afternoon and early evening. Expecting an earlier return late this evening around 05Z and linger through at least 18Z Thursday. There is a low-to- moderate confidence for IFR conditions early Thursday morning, yet confidence is not high enough to include in this TAF package, yet have mentioned SCT for the timeframe it has the greatest potential. SFO Bridge Approach...Later return of stratus Thursday morning, otherwise similar to SFO. Monterey Bay Terminals...VFR conditions are forecast to return by around 1930Z, KSNS has already scattered out. Onshore winds increase this afternoon before MVFR ceilings return late this evening and lower to IFR a bit later in the evening. There is the potential for LIFR conditions late in the night into Thursday morning, yet again confidence is not high enough to include in this TAF package. && .MARINE... (Today through Monday) Issued at 950 AM PDT Wed Aug 5 2026 Light to gentle south to southwesterly breezes will persist through Thursday along with seas between 2-6 feet. Winds will begin to increase again out of the northwest going into Friday with building seas and hazardous conditions for small craft returning for the upcoming weekend. && .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...KR LONG TERM....KR AVIATION...RGass MARINE...RGass 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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