Severe weather threat tomorrow

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Synopsis... A large-scale upper trough will develop eastward from the Plains on Wednesday morning, becoming oriented from the Upper Midwest to the Southeast by Thursday morning. Enhanced southwesterly flow ahead of the trough will overspread much of the Midwest, and decreasing with southward extent into the southern U.S. At the surface, a cold front extending from WI southwestward into western OK/northwest TX will sweep eastward during the forecast period. By Thursday morning, the front is expected to extend from western NY/PA toward Middle TN, southwestward toward the TX coast. ...Middle TN into the OH Valley Vicinity... Stronger vertical shear will be in place across the region, closer to the core of the upper trough and within the stronger surface pressure gradient associated with a low over Ontario. South/southwesterly low-level flow will bring a narrow corridor of upper 50s and 60s F surface dewpoints northward ahead of the eastward-advancing cold front. Heating will be limited by cloud cover and possibly early day showers. However, cooling aloft will support modestly steep midlevel lapse rates, and MLCAPE of a few hundred J/kg will be possible amid 30+ kt effective shear magnitudes. Transient supercells and briefly organized clusters could produce isolated strong storms capable of hail and strong gusts. Low-level instability will be limited, but enlarged, favorably curved surface-3 km hodographs suggest a brief tornado also could occur. ...AR into western TN/northern MS Vicinity... Additional thunderstorms are expected to develop along the front during the afternoon across AR and shift east/southeast into western TN and northern MS. Some guidance suggest an increase in hail and strong gust potential will accompany these cells. Stronger heating is expected along this corridor ahead of the front, resulting in steeper low-level lapse rates, while cooling aloft associated with the main upper trough supports steepening mid-level lapse rates. Effective shear magnitudes around 25-35 kt and favorable hodographs suggest some rotating cells will be possible. A narrow corridor of relative greater severe potential may exist within this corridor and an upgrade to Slight risk may be needed in subsequent outlooks if forecast confidence increases.

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