275
ACUS01 KWNS 181619
SWODY1
SPC AC 181617

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1117 AM CDT Sat Oct 18 2025

Valid 181630Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
FROM THE ARK-LA-TEX TO THE LOWER OHIO AND MISSISSIPPI VALLEYS...

...SUMMARY...
Scattered severe thunderstorms are possible mainly this afternoon
into tonight across parts of the Ark-La-Tex, Ozarks, mid to lower
Mississippi and lower Ohio Valleys.  Damaging winds, a few tornadoes
and hail may occur.

...Synopsis...
A southern stream shortwave trough will eject quickly
east-northeastward from TX/OK to AR/MO, prior to phasing with an
amplifying northern stream trough by tonight across the mid MS
Valley.  Downstream from the phasing troughs, a deepening surface
cyclone will develop northeastward tonight from the mid MS Valley to
Lower MI, as a trailing cold front surges southeastward from the
Plains into the mid-lower MS Valley.

...TX/OK today into the MS/OH Valleys through early Sunday...
Regional 12z soundings revealed a plume of 7.5-8 C/km midlevel lapse
rates (FWD-OUN-LMN) atop low-level dewpoints in the 60s, which is
already contributing to moderate buoyancy (MUCAPE up to 1500 J/kg)
as of mid morning.  As continued forcing for ascent with the lead
shortwave trough overspreads the moisture/buoyancy plume, ongoing
thunderstorms are expected to increase in coverage through the
afternoon from southern MO/IL to eastern OK/western AR and
north/northeast TX.  Initial storms will be in the form of
clusters/short line segments with upscale growth into a more
extensive squall line expected by later this afternoon/evening.

Buoyancy will increase some in the moisture plume through the
afternoon with surface heating in cloud breaks, and deep-layer
vertical shear will increase with the approach of the ejecting
midlevel trough.  Thus, the stronger embedded cells will have the
potential to produce large hail (1-1.75 inches in diameter) along
with an increase in the threat for wind damage as convection becomes
more linear.  The tornado threat is a bit more uncertain given the
early/messy start to convection this morning, and since low-level
shear will not be strong this afternoon in the warm sector as a
result of primary cyclogenesis not occurring until tonight from IL
into lower MI (north of the richer low-level moisture).  Still, a
couple of tornadoes may occur with embedded circulations.  There
will be the potential for more discrete supercells and a few
tornadoes ahead of the larger-scale line of storms from far east TX
into LA/southern AR and MS overnight where boundary-layer dewpoints
exceed 70 F and low-level shear increases.

Though buoyancy will be weak, rapidly strengthening wind fields
overnight and forcing for ascent along the synoptic cold front could
support a low-topped line of convection with the potential for wind
damage and possible a couple of embedded tornadoes from the OH
Valley into southeast Lower MI ~06-12z.

..Thompson/Supinie.. 10/18/2025

$$