Scattered severe thunderstorms are possible across parts of the Ohio Valley and Mid-Atlantic this afternoon and evening. Strong to severe wind gusts capable of producing wind damage should be the primary hazard, but isolated hail may also occur. Thunderstorms may bring heavy to excessive rainfall and possible flooding today over the northern Gulf Coast and upper Ohio Valley. Read More >
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363 FXUS66 KMTR 271917 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1217 PM PDT Wed May 27 2026 ...New SHORT TERM, LONG TERM... .KEY MESSAGES... Updated at 1215 PM PDT Wed May 27 2026 - Cooler, unsettled weather conditions continue through Thursday - Warming and drying trend Friday and beyond && .SHORT TERM... Issued at 1215 PM PDT Wed May 27 2026 (This evening through Thursday) We have already seen showers and an isolated thunderstorm develop late this morning across the Eastern Santa Clara Hills and in the Mountains of San Benito County. As daytime heating continues, we are expecting convection to fire up in the East Bay Hills, Eastern Santa Clara Hills, the Santa Cruz Mountains and the Central Coast (County of Monterey/San Benito) this afternoon and evening. This is as the atmosphere becomes more unstable with CAPE values between 100-400 J/kg. However, vertical wind profiles don`t favor organized convection, with little to no 0-6km wind shear. Therefore, probabilities for thunderstorms remain less than 10% through the afternoon and early evening. Any stronger cell (shower and/or thunderstorm) that develops over any one given location has the potential to produce 0.25"-0.50" per hour of rainfall. The mid/upper level low will begin to retrograde back over the Pacific tonight into early Thursday morning and begin to pull in PWAT values of around 1.00". This will increase rain chances offshore late tonight and then will move onshore along the Central Coast through Thursday morning. However, with the loss of daytime heating, the thunderstorm threat will lessen. Forecast rainfall amounts have increased in the Santa Cruz Mountains and Santa Lucia Range now having a greater than 60% probability of seeing more than 0.25" through Thursday afternoon (this would include rainfall from today). These probabilities of seeing greater than 1.00" (40%-75%) remain confined to the Santa Lucia Range. Conditions begin to dry out from north to south during the day Thursday as the mid/upper level low shifts further inland. However, rain showers look to linger over the Central Coast through the early evening. && .LONG TERM... Issued at 1215 PM PDT Wed May 27 2026 (Thursday night through next Tuesday) Cannot rule out rain showers to linger across the North Bay late Thursday night into early Friday morning as deeper moisture (PWAT values approaching 1.00") move across this region. In wake of the exiting trough, a warming and drying trend will kick off by Friday afternoon with temperatures gradually returning to near average this weekend as zonal flow develops over the region. Temperatures are currently forecast to warm above seasonal averages by Sunday and into the middle of the upcoming week. && .AVIATION... (18Z TAFS) Issued at 1122 AM PDT Wed May 27 2026 The cold core 500 mb low continues to straddle the CA/NV border. A spoke of 700 mb to 500 mb troughing/instability extending outward from the low center continues to move southward over the southern half of our forecast area at the moment. It`s cold for late May at the mandatory pressure levels 925 mb through 500 mb on this morning`s 12z Oakland upper air sounding: < 10th percentile for late May. With solar input and surface heating today, expect a few more showers along with isolated lightning in the unstable air. KMUX shows a recent isolated thunderstorm over northeastern Santa Clara county, drifting to the southwest. Will continue to closely monitor KMUX radar and satellite through today. The aforementioned 500 mb low and high precipitable water it has entrained (near 90th percentile) bring the potential for more wet weather tonight and Thursday. Will closely monitor radar and satellite imagery. Vicinity of SFO...VFR. East to northeast wind 5 knots shifts to westerly and increases to 15 to 22 knots in the afternoon with gusts diminishing below 20 knots beginning 03z this evening. Wind shifts to southeasterly 5 knots Thursday morning then to westerly 12 knots Thursday afternoon. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Lingering MVFR ceilings are expected to scatter out by the afternoon, if they have not already. Onshore moderate breezes (~10-14kt) will persist through the afternoon with the Salinas valley experiencing gusts up to 20kts. MVFR ceilings will return this evening (00-02Z). Light rain showers begin to approach the Monterey Bay coastline late Wednesday night with winds slightly diminishing. Medium confidence in the timing of the rain showers as they may arrive an hour earlier or later, though they are expected to stick around for the remainder of the TAF period. Winds begin to shift SE early Thursday morning. There is low confidence at this time that visibility will be impacted, however I wouldn`t be surprised if the rain showers cause a slight reduction to visibility (minimum 5SM). && .MARINE... (Today through Monday) Issued at 1005 AM PDT Wed May 27 2026 Northwesterly winds continue to diminish through today and overnight into widespread gentle to moderate breezes over the outer and inner waters. Wind gusts also become more moderate, with the outer northern waters experiencing locally strong gusts through Thursday morning. Rough seas with heights of 11-16 ft continue to abate through today and become more moderate (5-9 ft) by Friday morning. Another round of strong to near-gale force winds are expected to develop over the weekend with building rough seas again. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory until 9 AM PDT Thursday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...RGass LONG TERM....RGass AVIATION...Canepa/Navarrete MARINE...Navarrete/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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