112
ACUS01 KWNS 231952
SWODY1
SPC AC 231950

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0250 PM CDT Mon Sep 23 2024

Valid 232000Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS NORTHERN
ARKANSAS INTO THE LOWER OHIO AND TENNESSEE RIVER VALLEYS...

...SUMMARY...
Isolated strong to severe thunderstorms are possible this afternoon
into evening from the Ozarks into parts of the Tennessee and lower
Ohio Valleys.

...20z Update...
The previous forecast remains on track with only minor adjustments
needed based on recent observations and trends in guidance. Latest
surface observations and upper-air analyses show the gradual
organization of a surface low over northern AR/southern MO. The
frontal boundary draped from southeast MO into the upper OH River
Valley has begun to stall and is expected to gradually advance north
through the evening hours. VWP observations along the frontal zone
currently show relatively straight low-level hodographs, but
helicity should slowly improve through the 20-03 UTC period as
isentropic ascent along the front increases. As a result, the
convective environment should become more favorable for organized
convection - particularly during the 22-03 UTC period across far
southeast MO into far southern IL and western KY.

Latest high-res guidance suggests that storms developing along an
approaching cold front across north-central AR will intensify as
they migrate east towards this zone and should pose the primary
severe threat this evening. However, loosely-organized thunderstorms
recently developing within the mid-MS River Valley cast some
uncertainty onto this scenario due to the potential for overturning
portions of the downstream warm sector. This early convection may
see improving organization in the coming hours as mid-level flow
slowly improves late this afternoon, but limit storm longevity over
the past hour cast some uncertainty onto the propensity for severe
storms. Regardless, this stalled/warm frontal boundary will still
present the best corridor for a more focused severe event through
the evening hours, including the potential for a tornado or two. As
such, the 2% risk probabilities have been expanded east into western
KY. Consideration was given for 15% wind probabilities through this
corridor, but confidence in storm mode and coverage remains too
limited given the aforementioned concerns.

Farther east across southern KY and TN, the forecast remains on
track. See MCD #2097 for details regarding recent convective trends.

..Moore.. 09/23/2024

.PREV DISCUSSION... /ISSUED 1143 AM CDT Mon Sep 23 2024/

...Ozarks to TN/OH Valleys and southern Appalachians...
A positive-tilt upper trough will influence the region, with a
general increase in relatively strong deep-layer southwesterly
winds. Severe storms are possible this afternoon, particularly and
initially across the Ozarks including far south-central to southeast
Missouri, as well as far northern Arkansas and far southern
Illinois. This will be in vicinity of a weak surface wave and a
northward-shifting warm front as lingering morning convection
along/north of the Ohio River abates and shifts eastward.
Increasingly strong deep-layer winds could support some supercells.
Some hail is possible given the buoyancy/deep-layer wind profiles,
although mid-level lapse rates are not steep. Locally damaging winds
may also occur, with some potential for a tornado or two mainly near
the warm front.

Although uncertainties linger regarding destabilization and the
magnitude of the severe risk later this afternoon, portions of
southeast Missouri and far southern Illinois will continue to be
reevaluated into mid-afternoon (20Z update) for a potential risk
upgrade.

Farther east, isolated to scattered thunderstorms will probably
develop near the ridge tops of the southern Appalachians and
adjacent parts of the Carolinas Piedmont this afternoon. Moist low
levels coupled with heating will result in around 1000 J/kg MLCAPE.
Some modest multicell organization may occur due to adequately
strong upper-level westerly flow, with a few locally damaging wind
gusts a possibility.

$$