NH Spring/SH Autumn 2020 Discussion Thread

...DISCUSSION...

An outbreak of severe thunderstorms appears possible on Sunday
across parts of Louisiana, Mississippi, Alabama, and possibly into
Georgia by Sunday night. Tornadoes (potentially strong/long-tracked)
and widespread damaging winds are expected to be the primary
hazards.

...D4/Sunday: TX Gulf Coast eastward through the Southeast into the
Carolinas...

Ingredients for a potential severe thunderstorm outbreak appear
likely to come together Sunday into Sunday night. An ejecting
shortwave trough is forecast to take on a neutral to somewhat
negative tilt by Sunday afternoon as it moves quickly
east-northeastward across the Southeast states. Rich low-level
moisture will be drawn inland from the Gulf of Mexico in advance of
a deepening surface low that will move from the mid-MS Valley into
the Ohio Valley by Monday morning. Moderate destabilization in
conjunction with an 80-100 kt midlevel jet and 50-60 kt low-level
jet will result in a very favorable environment for organized
convection, including the potential for long-track supercells and a
corresponding strong tornado risk. Very strong low/midlevel flow
fields will also support widespread damaging wind potential.

Some uncertainty remains regarding the northward extent of the most
significant severe potential, given the presence of widespread
convection in advance of the ejecting shortwave. Guidance also
continues to trend slightly slower, with the GFS still a notably
fast outlier. A 30% probability contour has been introduced from LA
into central/southern MS/AL and southwest GA, where confidence is
highest in the outbreak potential at this time.

An organized severe thunderstorm threat will likely continue into
Monday morning, with the potential for damaging wind and/or a few
tornadoes likely spreading into portions of the Carolinas by 12Z
Monday.