SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1054 AM CST Tue Nov 24 2020

Valid 251200Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE LOWER AND MIDDLE MS...LOWER OH AND TN VALLEYS...

...SUMMARY...
Isolated strong to severe thunderstorms may occur Wednesday across
parts of the lower/mid Mississippi Valley into the Ohio/Tennessee
Valleys and Southeast. Locally damaging winds should be the main
threat, although a tornado or two also appears possible.

...Synopsis...

A mid/upper level shortwave trough centered over the Ozark Plateau
early Wednesday will lift northeast across the Midwest to the upper
OH Valley/central Appalachians by 12z Thursday. Surface low pressure
will move in tandem with the upper trough from MO toward the lower
Great Lakes while a trailing cold front pushes eastward across the
mid/lower MS valley and the lower OH/TN Valley. Ahead of the front,
southerly low level flow will continue to transport Gulf moisture
northward, with 60s F dewpoints reaching as far north a TN
potentially. Surface dewpoints in the 50s will be more common
farther north across the Ohio Valley vicinity. Surface heating will
be limited by cloudiness and showers ahead of the front, but cooling
aloft is expected to result in modest midlevel lapse rates.
Furthermore, strong shear profiles are forecast as winds veer with
height and 40-60 kt 850-700 mb southwesterly flow overspreads much
of the southern/central U.S. This should support at least isolated
strong-to-severe thunderstorms capable of strong/locally damaging
wind gusts across the lower/mid MS Valley to the OH/TN Valley. 

...Lower/Mid MS Valley to the OH/TN Valley Vicinity...

Higher-quality low level moisture will be confined to the lower MS
Valley into MS/AL on Wednesday. While stronger heating will be
limited by cloudiness and showers ahead of the cold front, modest
midlevel lapse rates atop rich boundary layer moisture should result
in at least weak surface-based instability (typically 750 J/kg or
less). Strong shear will reside over the region to aid in organized
convection. Deep layer flow will mainly be parallel to the front,
favoring line segments, but a couple of semi-discrete cells also are
possible. Strong forcing closer to the trough/surface low will be
shifting away from the region through the day, but the front and
weak buoyancy will be sufficient for strong-to-severe convection
into parts of MS/AL and middle TN through early evening. Storm mode
and quickly strengthening flow with height will mainly favor
damaging wind potential. However, where backed low level flow is
present, low level SRH will be enhanced and a tornado or two cannot
be entirely ruled out. 

Farther north, instability will be even weaker given overall
poorer-quality boundary layer moisture and a cooler environment.
However, steeper midlevel lapse rates with colder air aloft should
result in weak elevated instability. Stronger forcing and favorable
shear profiles may compensate somewhat for meager instability, and
at least a narrow line of near-surface-based convection closer to
the surface low and cold front is expected during the
afternoon/evening across parts of the lower OH Valley. Strong low
level wind field associated with low/midlevel jet streak will favor
bowing segments capable of isolated strong/damaging gusts.

..Leitman.. 11/24/2020

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