SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1107 AM CST Wed Nov 25 2020

Valid 261200Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST TX INTO SOUTHWEST LA EARLY FRIDAY MORNING...

...SUMMARY...
Isolated large hail may occur with thunderstorms that develop across
parts of southeast Texas and southwest Louisiana, mainly from
Thursday night into early Friday morning.

...Southeast States into New England...

A mid/upper shortwave trough over the central Appalachians/lower
Great Lakes vicinity Thursday morning will develop east/northeast
across the Mid-Atlantic and Northeast through Thursday evening. At
the surface, a cold front will extend from western NY/PA into
central AL and southwestward near the LA/TX Gulf Coast vicinity
Thursday morning. The front will not advance much across the
Southeast as the upper trough and weakening surface low track well
north of the region. In fact, a weak shortwave upper ridge will
develop over the south-central states in the wake of the ejecting
northeastern upper trough. This will allow for the cold front to
become diffuse, and in some places retreat northward as a warm front
as a southerly low level flow warm advection regime develops across
TX and into the lower MS Valley after 00z. The northern segment of
the cold front will shift eastward across New England and the
Mid-Atlantic through the afternoon, moving offshore by evening.
Showers and isolated thunderstorms are expected near/just ahead of
the front from the southern U.S. through much of the Atlantic Coast.
However, weak instability and modest shear will limit organized
severe potential. 

...Southeast TX into Southwest LA...

An upper trough will deepen over the western states Thursday, and
become increasingly cut-off over the Four Corners by Friday morning.
As this occurs, a surface trough is forecast to develop from
southwest TX into OK, resulting in increasing southerly return flow
across southern/eastern TX and the lower MS Valley by Thursday
afternoon. This will allow 60s F surface dewpoints to advance as far
north as roughly the I-20 corridor from eastern TX into MS by late
in the forecast period ahead of a cold front surging southward
across the southern Plains. Forcing for ascent will remain weak
across the region, and deterministic as well as
ensemble/probabilistic guidance varies, but isolated thunderstorms
could develop in this warm advection regime late in the forecast
period. If this occurs, increasing southwesterly shear and steep
lapse rates atop a near-surface cool layer could support elevated
supercells. While this threat is highly conditional on storm
development, elevated supercells could produce large hail, mainly
across southeast TX into southwest LA early Friday morning.

..Leitman.. 11/25/2020

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