Scattered severe storms with wind damage, large hail, and a few tornadoes will be possible this afternoon and evening across much of the Mid Atlantic and Southeast. Heavy rain may cause instances of flash flooding from eastern Kentucky to southern New York. Out west, dangerous heat will develop through Saturday, with record-breaking temperatures expected. Read More >
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369 FXUS66 KMTR 281137 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 437 AM PDT Wed May 28 2025 ...New AVIATION... .SYNOPSIS... Issued at 253 AM PDT Wed May 28 2025 Near normal temperatures are anticipated through mid-week with impactful heat by Friday. The fire weather threat will elevate through the end of the week. Thereafter, temperatures are expected to return to near normal values. && .SHORT TERM... Issued at 253 AM PDT Wed May 28 2025 (Today and tonight) Key Messages -May Gray with coastal drizzle -Seasonable temperatures -Stronger onshore winds May Gray alert in effect this morning. Overnight satellite fog product shows a very well defined marine layer hugging the coast and pushing well inland. Coastal profilers put the depth 1,500-1,700 feet. Given the very moist low levels added drizzle to the forecast mainly for coastal areas this morning. Patchy fog will also be possible along the immediate coast. It will take some time, but inland areas will see the marine layer roll back to the coast. The slow erosion will be due to a decent onshore gradient (SFO-SAC) greater than 4mb. Coastal areas on the other hand will struggle to see much in the way of sunshine this afternoon. As such, definitely a temperature contrast today from the coast to inland locations - Upper 50s to near 70s coast and 70s to upper 80s inland. The marine layer will push inland again tonight with a similar depth and coverage. Coastal drizzle/patchy fog will be possible once again. Not only does the marine layer provide a temp contrast, but also a humidity contrast in the vertical. Higher elevations will remain on the drier with moderate to poor humidity recovery. Lastly, the increasing onshore gradient will result in stronger winds this afternoon and overnight. Winds will be strongest over the coastal waters, immediate coast, and inland gaps/passes. Not strong enough for a wind advisory, but gusts 30-40 mph seems plausible. && .LONG TERM... Issued at 353 AM PDT Wed May 28 2025 (Thursday through Tuesday) Key Messages -Above normal temperatures through Saturday -Impactful heat Friday with Heat Advisory - Santa Cruz Mts added -Cool down Sunday and early next week An upper level ridge will build across the Bay Area Thursday. The orientation of the ridge (SW to NE) is being squeezed by a cut- off low near Baja and an upper trough near Gulf of AK. This upper ridge will peak Friday before weakening over the weekend. The airmass associated with the ridge is rather toasty with 850mb temps reaching the mid 20C, which is 5-10 degrees above normal. Under a fully mixed atmosphere or no marine influence those values would yield max temperatures over 100 degrees. That`s what the forecast has for far interior locations on Friday, 100-105 degrees for a max temp. Other inland locations will also feature above normal temps with highs in the upper 80s to upper 90s. HeatRisk values remain in the "moderate" category with pockets of "major". With this forecast update decided to include the Santa Cruz Mts for the Heat Advisory on Friday. Places like Boulder Creek and Ben Lomond will be in the upper 90s. The ridge begins to weaken by Saturday with cooler temperatures developing. Saturday will be a transition day with more widespread cooling expected by Sunday. As such, interior N and E Bay, and interior Central Coast may need one additional day of a Heat Advisory, but will hold off for now. Not expecting this to be a record breaking heat event, but some of the hottest temperatures of the year for some locations. Heat safety protocols should be followed for those with outdoor plans and/or those sensitive to heat Thursday through Saturday. Temperatures finally return to seasonal averages by Sunday and below seasonal averages by early next week. As noted on the last two forecast discussions one low chance high impact scenario we continue to monitor closely will be high-based convection Saturday potential over the Central Coast. Longer range model guidance continues to advertise a northward push of some upper level moisture. The cut-off low spinning over SoCal will be the main driver of this moisture push. Given the uncertainty that typically follows cut-off lows will not add any convection to the forecast at this time. Best way to describe this would be a non-zero chances. && .AVIATION... (12Z TAFS) Issued at 437 AM PDT Wed May 28 2025 Coastal stratus along with patchy fog /MVFR-LIFR/ and onshore winds prevail this morning. HREF output show it`ll be slow clearing along the immediate coastline through morning, best probability for VFR will be far inland locations and during the afternoon closer to the coastline. Coastal stratus and fog will move inland tonight and Thursday morning. Vicinity of SFO...IFR stratus ceiling continuing to late morning, then gradually lifting to MVFR to early afternoon based on recent HREF and RAP model output. West wind increasing to 15 to 25 knots late morning to mid evening today. Stratus /MVFR/ possibly IFR ceiling returns tonight and Thursday morning. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...IFR-LIFR in stratus continuing to late morning, cloud ceilings gradually improving thereafter to MVFR-VFR during the afternoon. Stratus /IFR/ returns tonight and Thursday morning. West to northwest winds 5 to 15 knots. && .MARINE... (Today through Monday) Issued at 253 AM PDT Wed May 28 2025 Northwest winds will increase over the coastal waters today with gale force gusts developing over the southern inner coastal waters. Strong and gusty northwest winds will continue to pose a threat to small craft due to steep wind waves through much of the forecast period. && .FIRE WEATHER... Issued at 330 AM PDT Wed May 28 2025 Elevated fire weather concerns will develop and persist into the weekend. Despite the marine layer bringing decent moisture to lower elevations, higher elevations remain dry with moderate to locally poor humidity recovery the next few days. As daytime temperatures ramp up Thursday, peak Friday, moderate Saturday, daytime minimum humidity will follow a similar path with low values. Onshore flow will bring occasional gusty winds, but not strong enough or widespread enough to warrant a Red Flag Warning. Regardless people should be mindful with open flames, secure tow chains, and avoid activities that could spark a grass fire. This is particularly true given the slight uptick in vegetation fires over the past couple of weeks. As noted above, we continue to monitor a non-zero chance for high-based convection on Saturday for the Central Coast. Concern would be dry lightning on the heels of a hot and dry spell. MM && .CLIMATE... Issued at 1128 PM PDT Tue May 27 2025 Record high temperatures at the long term climate stations Friday, May 30th and Saturday, May 31st. Station May 30th May 31st Santa Rosa 100F 1910 99F 1970 Kentfield 101F 1950 102F 2001 Napa 104F 1910 103F 2001 Richmond 94F 2001, 1978 95F 2001 Livermore 108F 1910 104F 2001, 1910 San Francisco 91F 1978 90F 2001 SFO Airport 95F 2001 91F 2001 Redwood City 101F 1950 99F 2001 Half Moon Bay 67F 1978, 1941 77F 1997 Oakland downtown 98F 1978 89F 2001 San Jose 102F 1910 98F 1970 Salinas Airport 95F 2001 90F 1997 King City 102F 2001 100F 2001 && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 11 AM to 8 PM PDT Friday for CAZ504-506-510- 512>518-528. PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for SF Bay N of Bay Bridge. Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Thursday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM. Small Craft Advisory from 9 AM to 9 PM PDT Thursday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm. Small Craft Advisory from 9 AM this morning to 3 AM PDT Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Friday for Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 9 AM this morning to 3 PM PDT this afternoon for Pt Pinos to Pt Piedras Blancas 0-10 nm. Gale Warning from 3 PM this afternoon to 9 PM PDT Thursday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 PM Thursday to 3 AM PDT Friday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...MM LONG TERM....MM AVIATION...Canepa MARINE...Canepa 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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