SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1234 AM CDT Wed Sep 08 2021 Valid 081200Z - 091200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE NORTHEAST... ...SUMMARY... The potential for a few tornadoes and scattered damaging winds appears most probable across portions of the Northeast States from mid-afternoon through evening. ...Northeast and Mid-Atlantic States... A shortwave impulse embedded within the broader longwave trough will progress from the Upper Midwest to the Lower Great Lakes by this evening. This will aid in maintaining convergence along a progressive cold front that arcs from an occluding surface cyclone across northeast ON into western QC. South to southwesterly low-level flow will advect boundary-layer moisture from rich PW values across the Carolinas. This just-in-time moisture return should result in a plume of mid to upper 60s surface dew points from the Hudson Valley to the Mid-Atlantic Piedmont/Coastal Plain. While convection will likely linger within the warm conveyor along the cold front during the morning to early afternoon, activity should intensify during the mid to late afternoon as it impinges on the more unstable air mass east of the northern and central Appalachians. Low-level hodographs should be most enlarged across eastern NY to western New England, coincident with the increasingly narrow extent of the modest buoyancy plume. Farther south where MLCAPE increases, forecast soundings continue to indicate weakness in the wind profile from about 800-700 mb, yielding prominent M-shaped hodograph structure. A mixed mode of supercells with low-level updraft rotation embedded within clusters is anticipated, that should spread east into the evening, weakening from north to south after dusk. A couple tornadoes seem probable along with strong gusts producing scattered damaging winds and isolated severe hail. The cat 2/SLGT encompasses the most likely corridor for this activity to occur, but a broader lower probability will frame at least an isolated severe threat during the afternoon and evening. ...Northwest FL including the Panhandle... Increasingly numerous thunderstorms are expected across parts of the central Gulf this morning in association with a drifting mid-level disturbance. This setup has the potential to generate an MCV with an attendant belt of strengthening low-level flow overspreading the northeast Gulf Coast area later tonight. Should this occur, enlarging low-level hodographs will support potential for a tornado or two and locally damaging winds, yielding an upgrade to cat 1/MRGL. ...Concho Valley and Edwards Plateau of TX... Isolated to scattered late afternoon thunderstorms are possible along the west/east-oriented portion of the Eastern to Southern U.S. cold front. Here, a plume of 2000-2500 J/kg of MLCAPE should develop amid modest north-northeasterly steering flow. The ample buoyancy atop an inverted-v thermodynamic profile could foster strong to locally severe wind gusts and marginally severe hail through about dusk with weakly organized southwest-propagating multicells. ...South-central AZ... A similar setup to what occurred on Tuesday across southwest NM into far southeast AZ is expected to shift west into south-central AZ during the late afternoon to early evening. Overall effective shear values are expected to be slightly less at about 30-35 kts with a hotter boundary layer as well. As such, hail magnitudes will probably be subdued, but could still become marginally severe. The main hazard should be localized severe wind gusts given ample buoyancy over the Gila Valley, as mostly discrete convection spreads west off the higher terrain of southeast AZ. ..Grams/Squitieri.. 09/08/2021 Read more LIVE: spc.noaa.gov
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