Day 1 Severe Weather Outlook

Valid 241630Z – 251200Z


The threat for tornadoes, large hail, and damaging winds will be
focused this afternoon and evening across the Tennessee Valley.

…TN Valley this afternoon/evening…
A midlevel shortwave trough over AR/MO this morning will move
eastward to the TN Valley by this evening, as an associated surface
cyclone in OK develops eastward along a rain-reinforced boundary
near the southern TN border. Along and south of this surface
boundary, dewpoints will remain in the mid 60s through the
afternoon, beneath midlevel lapse rates of 7-8 C/km per 12z
soundings. The net result with daytime heating in cloud breaks will
be moderate buoyancy (MLCAPE 1000-1500 J/kg) within the warm sector,
in advance of the surface cyclone/midlevel trough.

In the wake of the elevated convection this morning, additional
thunderstorm development is expected by mid afternoon in the
vicinity of southwestern TN/northern MS, south of the ongoing
elevated storms in the left-exit region of the midlevel jet over
northeast AR. Storms will subsequently spread eastward across
northern AL and southern middle TN through the evening. Strong
deep-layer vertical shear with long hodographs and effective bulk
shear of 50-60 kt, as well as low-level hodograph curvature with 0-1
km SRH near 200 m2/s2, will favor supercells. Low-level shear could
be enhanced some along the residual rain-cooled boundary that will
likely shift northward into southern middle TN by mid afternoon.
Farther south, some vertical mixing of moisture could introduce
somewhat larger (15-20 F) temperature-dewpoint spreads from central
MS into central AL this afternoon. Thus, the most favorable
corridor for tornadic storms will be in the zone of greater
low-level shear and retained low-level moisture near the rain-cooled
boundary, closer to the TN border this afternoon/evening. The
favorable near-storm environment, in combination with an expected
discrete/cluster storm mode, may support a strong tornado or two.

..Thompson/Moore.. 03/24/2020


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