SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0740 AM CDT Sun Oct 25 2020 Valid 251300Z - 261200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Synopsis/Discussion... In mid/upper levels, heights will fall across much of the central/ southern Rocky Mountains, Great Basin and Southwest through the period, as substantial troughing now over the interior Northwest digs southeastward and intensifies further. This will result in a broad fetch of southwest flow aloft from AZ across the southern/ central High Plains to the upper Great Lakes. Strong cooling aloft ahead of the western CONUS trough will steepen low/middle-level lapse rates across the Four Corners region today into this evening, combining with weak but sufficient low-level moisture to yield MLCAPE in the 100-400 J/kg range. Well-mixed afternoon boundary layers beneath strengthening midlevel currents may promote strong gusts in a few cells, but organized severe potential appears too minimal for an outlook. At 11Z, the surface chart showed a wavy frontal zone, moving slowly toward the south as a cold front across NC and quasistationary elsewhere across northern GA, eastern AL, and the LA shelf waters of the Gulf. Frontolysis is underway and will continue on the western segment of this boundary over TX coastal waters and deep south TX, while frontogenesis already drawn over the South Plains and Red River regions also continue. The latter front will sharpen and sag southward across the southern Plains through the period. By 12Z, a frontal-wave low may develop near ACT, with the cold front arching southwestward to westward across the southern Hill Country, Edwards Plateau and Trans-Pecos regions. A stationary to very slow warm front will extend from the wave over the Arklatex region. Late overnight and northwest of the surface front, increasing elevated moisture and isentropic lift within a strengthening warm-advection plume will combine with frontal forcing, to increase chances for thunderstorms embedded within an earlier-developing precip plume. Meanwhile, a weak southern-stream perturbation now over the Carolinas will continue to move east-northeastward and offshore from the Tidewater area by this evening. General-thunder potential will diminish quickly behind this trough, in a region of strong mid/upper drying shown on moisture-channel imagery. Farther south, isolated, disorganized thunderstorms will be possible in a very moist and weakly capped air mass, but with marginally supportive midlevel lapse rates, across parts of southern/central FL. ..Edwards/Mosier.. 10/25/2020
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