SPC AC 251954
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0254 PM CDT Mon Sep 25 2023
Valid 252000Z - 261200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
FLORIDA PENINSULA AND SOUTH TEXAS TO SOUTHWEST LOUISIANA...
Isolated severe thunderstorms remain possible across southern parts
of Texas, southwestern Louisiana, and the Florida Peninsula late
this afternoon into this evening.
No changes have been made to the severe probabilities. Isolated
strong to potentially severe thunderstorms remain possible across
parts of the FL Peninsula, and also across southern parts of Texas
into southwest LA. See the previous discussion below for more
information. Also see MCD 2196 for more information regarding the
short-term threat near the upper TX coast.
.PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Sep 25 2023/
...Southern Texas/southwest Louisiana...
Multiple areas of widely scattered showers and thunderstorms,
generally in a weakening/diminishing trend through mid/late morning,
exist across the region. Additional widely scattered thunderstorm
development is expected to uptick in coverage and intensity later
this afternoon, influenced by the southward-sagging front as well as
several zones of outflow/differential heating. Multicellular storms
will be common, with some potential for a few supercells
particularly with westward extent across south-central/southwest
Texas toward the Rio Grande, where deep-layer shear and buoyancy
will be a bit stronger and where large hail potential is more
apparent. This is aside from the potential for isolated severe wind
gusts that will more broadly exist across the region.
Scattered thunderstorms are expected to develop across the region
this afternoon. Localized strong/severe wind gusts are possible
along with the possibility of marginally severe hail. This regime is
the east of upper troughing over the central/northeast Gulf of
Mexico, with a moist environment (PW 1.75-2.25-inches) existing
across much of the Peninsula, with sea breeze boundaries focusing
increasing diurnal thunderstorm development. While deep-layer winds
will be weak, veering with height will contribute to 20-30 kt
effective-shear magnitudes, supporting multicellular storm
organization. Convection should diminish in coverage and strength
after sunset as a combination of nocturnal cooling and increasingly
prevalent outflow air stabilizes the boundary layer inland.
...Southeast MN/western WI/northeast IA/northwest IL...
A few funnels may occur this afternoon across the region in relative
proximity to the southeastward-moving upper low (-16C at 500mb),
focused near the surface occluded front that will be located near
the Mississippi River, and generally oriented parallel to it. There
is where low-level buoyancy including 100-125 J/kg 0-3 km CAPE will
be maximized with ambient vorticity. While a tornado cannot be
entirely discounted, the potential for such currently appears to be
very low, while funnels/briefly strong storms are otherwise
plausible within the weak vertical shear environment (effective/0-6
km shear magnitudes less than 20 kt).
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