Severe thunderstorms are forecast today in parts of the Ohio Valley southward through the southern Appalachians and northeast Gulf Coast. Severe thunderstorms are possible this evening/tonight east of the Appalachians from the Carolina Piedmont northward into parts of the Mid-Atlantic states.
In mid/upper levels, a synoptic-scale trough is evident in moisture channel imagery from MN/IA across the Ozarks and southwestward over south TX, with embedded vorticity max and remnant low over the western Ozarks region. This trough will move east-northeastward to a 00Z position from Upper MI to the IL/IN border, western TN, MS, and southeastern LA. By 12Z the trough should lost amplitude, but still remain large and well-defined, from southern ON to WV, the Carolinas, and southern/eastern GA. At the surface, 11Z analysis showed an elongated surface cyclone in the PAH-MEM corridor. A more-coherent low is forecast to consolidate through midday then move northeastward to near the CLE/CAK area by 00Z, then over or very near VT by 12Z. The associated leading cold front was drawn from the low across northern/southwestern AL and south of southeastern LA over the Gulf. A secondary/reinforcing cold front extended southwestward over AR. By 00Z, the main front should reach eastern OH, WV, the western Carolinas, and central/southern GA. By 12Z, the front is forecast over the southeastern NY/NJ area, then over Atlantic waters to south FL. A warm front, drawn initially in wavy fashion over eastern TN and western/northern NC — will shift northward erratically through the afternoon, catching up to a synoptic boundary initially extending from the low east-northeastward across northern portions of KY/WV/MD.
The combined warm front then should move northward through much of the Mid-Atlantic region. Upper Ohio Valley, Mid-Atlantic to southeastern CONUS… Scattered thunderstorms are expected to move from southwest to northeast across the outlook area through this evening, offering a primary threat of damaging to severe gusts, but with a few tornadoes also possible. A broken, messy band of precip and embedded thunderstorms is ongoing ahead of the front from portions of southeastern TN across the western FL Panhandle, with at least isolated severe potential remaining in a low-CAPE/high-shear setting. Refer to the remaining portions of watches 57-59, and accompanying mesoscale discussions, for more on the near-term scenario. An extensive shield of clouds/precip is apparent in a prefrontal low-level warm-advection/moisture-transport zone from eastern TN northward over much of KY/OH/IN.
A narrow corridor of destabilization is expected behind this precip and ahead of the low/front today, related to pockets of surface-diabatic heating and theta-e advection in the warm sector. This and weak MLCINH will offset modest midlevel lapse rates enough to support scattered thunderstorms along/ahead of the surface cold front, including prefrontal confluence/convergence lines. Convection generally will assume quasi-linear configurations with embedded LEWPs, bowing segments, and perhaps a few supercells possible. The environment will be characterized by strong deep-layer/speed shear and modest but sufficient buoyancy, with 500-mb winds strengthening to more than 70 kt over much of the central Appalachians region, and 45-60 kt of 850-mb flow crossing the same area. Buoyancy fields will be rather fragmented, but with general 500-1000 J/jg MLCAPE values spreading northeastward over eastern KY/OH and over areas from the Blue Ridge eastward. A relative min in low-level theta-e and buoyancy is likely in higher elevations from southwestern VA northeastward, but with at least marginal instability to support convection. Bands of convection should shift/form east of the mountains with time as well, also offering a dominant wind threat and secondary tornado potential in the strong-shear environment. Overall severe potential is expected to diminish after dark, and as the stronger upper support and mass response ejects northeastward in step with the trough aloft.
