SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CST Wed Dec 23 2020 Valid 241200Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS FAR EASTERN SC...EASTERN NC...AND FAR SOUTHEAST VA... ...SUMMARY... Severe thunderstorms are expected across the Mid-Atlantic States Thursday afternoon and evening. Isolated severe thunderstorms are also possible across portions of southeast Alabama, southwest Georgia, and Florida Thursday. ...Synopsis... A deep upper trough will extend from western Ontario southwestward through TX early Thursday morning. A shortwave trough embedded within the larger upper trough is expected to eject eastward across the Lower MS Valley before arcing more northeastward into the TN Valley. Evolution of the embedded shortwave will help induce a neutral tilt to the upper trough by Thursday afternoon, and a slightly negative tilt and closed upper circulation over the OH Valley by late Thursday night/early Friday morning. The maturing process of the upper trough will also result in further strengthening of the winds throughout its periphery. By early Friday morning, 100+ kt 500-mb winds will likely extend from the mid MS Valley southeastward/eastward through the base of the trough over the Southeast and then back northeastward into the Northeast. Very intense low-level flow is also expected, with 60+ kt at 850-mb extending from the Carolinas through the Mid-Atlantic into Quebec. Surface low associated with the embedded shortwave trough is forecast to begin the period over central AL before racing northeastward throughout the day. By early Friday morning, this low will likely be over western NY. This low is also expected to deepen during the period, helping to induce moisture return across the Mid-Atlantic. ...Mid-Atlantic States... Moisture return ahead of surface low and its attendant cold front is expected to net low 60s dewpoints across the Carolinas and southeast VA by the late afternoon/evening. Heating will be tempered by widespread cloud cover and lapse rates will remain modest. However, the anticipated moisture return should still be sufficient for modest instability by the afternoon. At the same time, very impressive kinematic profiles will be in place over the warm sector, with 50-70 kt 850+ mb flow contributing to large, looping low-level hodographs. 0-1 km storm-relative helicity will likely exceed 250 m2/s2 over the warm sector. Any discrete/semi-discrete storms that develop within this environment should become supercellular and pose a threat for tornadoes. However, several factors are difficult to ascertain at this forecast range, including the speed of the cold front, quality of the moisture return, and coverage of surface-based, warm-sector storms. These factors preclude introducing higher tornado probabilities with this outlook, but upgrades may be needed in subsequent outlooks. Additional severe potential will exist along the front as it moves through the region. Both damaging wind gusts and QLCS tornadoes are possible along the front as it moves through the region. Higher wind probabilities may also be needed in later outlooks once the amount of buoyancy ahead of the front become more certain. ...Portions of GA and FL... Modest severe potential is anticipated early Thursday along and ahead of the front as it moves across the FL Panhandle and southeast AL/southwest GA. In this region, modest instability and strong flow will likely support a few strong/severe storms. Similar environmental conditions, but with less low-level shear, could also contribute to a few strong/severe storms across the FL Peninsula as the front moves through. ..Mosier.. 12/23/2020
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