120
ACUS01 KWNS 251311
SWODY1
SPC AC 251308

Day 1 Convective Outlook RESENT 1
NWS Storm Prediction Center Norman OK
0808 AM CDT Wed Sep 25 2024

Valid 251300Z - 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 are possible this afternoon from parts of the
Southeast and central/southern Appalachians to the Texas/Louisiana
Gulf Coast. Some tornado threat may develop across the Florida
Peninsula by this evening, in association with Tropical Cyclone
Helene.

...Southeast and southern Appalachians...
Widespread precipitation is expected from parts of the Southeast
into the southern Appalachians, due to the combined influence of the
mid/upper-level flow to the west and moisture streaming north from
the Gulf of Mexico and Helene. While this will tend to limit
available buoyancy in some areas, strong to locally severe storms
will be possible with initial development, with preconvective MLCAPE
of around 1000 J/kg possible. This will generally be coincident with
favorable deep-layer shear, especially across the southern
Appalachians vicinity where a few supercells could occur pending
sufficient destabilization. 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 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...
Helene`s wind field is forecast to be rather large, especially on
the east side of the circulation, associated with what is expected
to be a strengthening Helene through the afternoon and night.
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. Most guidance suggests that instability will
remain too weak for an organized severe threat, although rather
strong deep-layer flow/shear could support a strong storm or two
with locally gusty winds and small hail. Subsequent outlooks will
reevaluate the possibility of introducing low severe probabilities.

...Upper Ohio Valley to the Lower Great Lakes...
Weak to locally moderate buoyancy may develop later today from parts
of the upper Ohio Valley into the lower Great Lakes region, between
a weakening cold front approaching from the west, and a slow-moving
warm front draped from central Pennsylvania into western New York.
Moderate southwesterly midlevel flow will support effective shear of
35-45 kt, sufficient for storm organization. However, with
persistent cloud cover and mid-level lapse rates expected to remain
rather weak, storm intensity and any attendant severe threat could
be relatively limited. Confidence in sufficient destabilization
remains too low to add severe probabilities.

..Guyer/Broyles.. 09/25/2024

$$