221
ACUS01 KWNS 251957
SWODY1
SPC AC 251955

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Wed Sep 25 2024

Valid 252000Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
GULF COAST INTO THE SOUTHERN/CENTRAL APPALACHIANS AND FLORIDA
PENINSULA...

...SUMMARY...
Isolated severe storms remain possible this afternoon from parts of
the Southeast and central/southern Appalachians to the
Texas/Louisiana Gulf Coast. Some tornado threat may still develop
across the Florida Peninsula by this evening, in association with
Hurricane Helene.

...20Z Update...
The only changes made to the Day 1 Convective Outlook were to trim
thunder and severe contours across the Gulf Coast into the OH
Valley, where lightning and strong wind gust coverage should become
increasingly sparse through the day. Otherwise, the previous
forecast (see below) remains on track.

..Squitieri.. 09/25/2024

.PREV DISCUSSION... /ISSUED 1143 AM CDT Wed Sep 25 2024/

..Southeast and southern Appalachians...
The influence of the upstream mid/upper-level trough and moisture
streaming north from the Gulf of Mexico and Helene will lead to
widespread precipitation across parts of the Southeast and southern
Appalachians. This will tend to limit available buoyancy in some
areas, but strong to locally severe storms may occur. Favorable
deep-layer winds/shear exist, especially across the southern
Appalachians vicinity where a few semi-discrete supercells could
occur aside from more prevalent quasi-linear convective bands.
Locally damaging wind gusts and perhaps a tornado could accompany
the strongest storms, before low/mid-level lapse rates and buoyancy
become increasingly weak with time, and an outflow-reinforced
effective front sags southward across the region.

...Texas Gulf Coast/Middle Gulf Coast...
Somewhat stronger diurnal destabilization will be possible from
parts of central/east Texas into Louisiana, and perhaps into
Mississippi, with MLCAPE potentially increasing above 1500 J/kg.
Isolated to widely scattered thunderstorm development will be
possible near a southward-moving cold front. Effective shear will
generally range from 25-35 kt, and a few modestly organized storms
are possible. Isolated damaging gusts could accompany the strongest
storms within this regime.

...Florida Peninsula and Keys...
Hurricane Helene`s wind field is forecast to be rather large,
especially on the east side of the circulation, associated with a
strengthening Helene through the afternoon and tonight. Reference
the National Hurricane Center for the latest Helene details. This
scenario will result in modestly strengthening low-level shear/SRH
across the Florida Peninsula during the day, but more so into the
evening and overnight after the peak diurnal instability cycle.
Instability will likely remain rather weak overall, and details
regarding the intensity of any outer rain bands remain uncertain.
However, some tropical-cyclone tornado threat could evolve across
parts of the Florida Peninsula and Keys, mainly into tonight.

...Eastern Washington/northern Idaho/northwest Montana...
While buoyancy is expected to remain quite weak, relatively steep
mid-level lapse rates will support thunderstorm potential late this
afternoon through early evening from eastern Washington into
northern Idaho and northwest Montana, in advance of the approaching
shortwave trough. Strong deep-layer flow/shear could support a
locally severe storm or two with gusty winds and possibly some hail.

$$