Extreme heat continues across the Southwest as temperatures may top 120 degrees. The heat may expand across the West and south-central U.S. into the middle of the month. Severe thunderstorms capable of severe wind gusts and large hail will be the primary hazards today across the northern Plains into the upper Midwest. Rainfall could be locally heavy across the Eastern U.S. today. Read More >
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173 FXUS66 KMTR 040848 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 148 AM PDT Tue Aug 4 2026 ...New SHORT TERM, LONG TERM... .KEY MESSAGES... Updated at 148 AM PDT Tue Aug 4 2026 - Moderate HeatRisk in the interior today, becoming patchy midweek - Elevated fire weather threat across the interior North and East Bays, and the Diablo and Santa Lucia ranges through the week - Widespread Moderate HeatRisk looks to return for the end of the work week. && .SHORT TERM... Issued at 148 AM PDT Tue Aug 4 2026 (Today and tonight) The southerly surge of stratus that arrived earlier on Monday, has allowed for stratus to become more widespread this morning. Nearly all of our coastline has low clouds along it, with the stratus penetrating inland. The Monterey Bay along with the majority of the Salinas Valley has filled in, is slowly creeping into Bay Area. Expect the marine layer to about 800-1000ft, which should keep high temperatures for coastal communities and areas in or under the marine layer reasonable. Clouds will begin retreating to the coast by mid to late morning, leaving mainly clear skies across the region. In terms of the upper level pattern, high pressure will slowly take hold of the forecast. 850mb temperatures today, look to to be between 24-29C, warmest across the interior. Expect temperatures to a bit cooler than yesterday for areas influenced by the marine layer, while other locations remain hot. Patchy Moderate HeatRisk exists interior North Bay and interior Monterey, with areas to widespread Moderate HeatRisk for interior East and South Bays. Opted to hold off an issuing a Heat Advisory for these locations tonight until we get a better visual on the marine layer expansion since that could put interior temperatures at risk. && .LONG TERM... Issued at 148 AM PDT Tue Aug 4 2026 (Wednesday through Monday) No major changes to the forecast as high pressure will continue to build into the region and then hold through at least Saturday. Temperatures will may decrease a more degrees on Wednesday, but it will be dependent on the marine layer. Interior locations will still be warm, but likely have temperatures in the 90s, perhaps cracking 100 in a few spots. Warmer and dryer weather starts to return on Thursday as the ridge strengthens. Looking at models, 850mb temps don`t really deviate too much. We`re still looking at that airmass being warm, around 27-30C, depending on the model. Overnight lows would be mild, especially in the thermal belts/mountains. And day time highs would climb back into the 90s and low 100s. The HeatRisk projection looks to have widespread Moderate HeatRisk for interior slots, with pockets of Major HeatRisk. Heat Advisories may be needed. && .AVIATION... (06Z TAFS) Issued at 941 PM PDT Mon Aug 3 2026 VFR will continue through the forecast period for the interior South Bay terminals, then IFR/LIFR developing around 10z for the North Bay and Bay Area terminals. IFR/LIFR ceilings returned earlier than expected to the Monterey Bay sites and will persist until early Tuesday afternoon. Vicinity of SFO...VFR until at least midnight, with high confidence that IFR/LIFR ceilings will develop overnight. Given the earlier onset across Monterey Bay sites, there`s a slight chance that stratus returns closer to 08z than 10z. High confidence that IFR ceilings persist until late morning with a slight chance of lingering into the early afternoon. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...IFR/LIFR ceilings returned a little sooner than expected with high confidence of persisting into the early afternoon. VFR through the remainder of Tuesday afternoon once they lift with a sunset return Tuesday evening. && .MARINE... (Tonight through next Sunday) Issued at 941 PM PDT Mon Aug 3 2026 Light to gentle breezes have set in across our outer waters with breezier south winds at times and pressure gradient forced onshore flow across the coastal waters tonight. Northwest seas will continue to ease and become 4-8ft for the remainder of the work week. Northwest winds begin to increase and become moderate by the end of the week into the weekend, with increasing seas responding by the weekend. && .FIRE WEATHER... Issued at 420 PM PDT Mon Aug 3 2026 Near critical fire weather conditions continue through this evening, with elevated fire weather conditions persisting through the middle of the week, and potentially a return of near critical conditions later in the week. Temperatures remain around 10 to 15 degrees above normal across the interior (except for Wednesday, with near normal temperatures) through early next week with highs in the upper 80s to 90s. No major changes to the forecasted dry conditions. Daytime humidity retention remains poor across the interior (20-30%) with humidity values dropping into the 10s across the interior Central Coast, East Bay Hills/Valleys, and the higher elevations. Portions of the interior Central Coast may see daytime humidity values drop into the single digits Tuesday, then again towards the end of the week into the weekend. Overnight RH recovery remains poor at locations above 2,000 feet with values between 25 to 40% expected with some favored locations struggling to reach even 25%. This will be particularly true across the Mayacamas, highest peaks of the East Bay Hills, the Diablo Range, the Santa Cruz Mountains, the Santa Lucia and Gabilan Ranges. Nocturnal drying (rapid decrease in RH through the pre- dawn hours) may also transpire which will increase the burn period or time in which fire behavior may remain active. Energy Release Component (ERC) values are projected to climb above the the percentile across the interior Central Coast, Mid Coast to Mendocino (North Bay), and Diablo- Santa Cruz (Diablo Mountains and Santa Cruz Mountains) zones by the middle of the week. Diurnally breezy onshore winds are expected along the coast, mountain gaps and passes, and along the ridgelines each afternoon/evening. With near critically dry conditions and above normal temperatures expected, individuals across these areas are advised to avoid activities that may spark a fire. Fire crews are urged to exercise extra caution when executing any prescribed burns, especially where fuels, topography, and weather align. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...KR LONG TERM....KR 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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