Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0745 AM CDT Wed Mar 19 2025
Valid 191300Z - 201200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR PARTS OF CENTRAL/NORTHERN ILLINOIS AND WEST
CENTRAL INDIANA...
...SUMMARY...
Scattered severe thunderstorms are possible this afternoon/evening
from central/northern Illinois to western Indiana. A few tornadoes,
large hail, and damaging wind gusts will be possible.
...IL/IN this afternoon into early tonight...
A deep (989 mb) cyclone near the northeast KS/northwest MO border
will move northeastward to northern IL by this evening and Lower MI
overnight, in conjunction with a deep midlevel trough and 100+ kt
midlevel jet streak. Elevated convection is ongoing this morning in
a zone of focused ascent with warm advection/frontogenesis across
IA, where isolated large hail may occur with MUCAPE around 500 J/kg
and steep midlevel lapse rates/cool midlevel temperatures. The warm
sector of the cyclone is characterized by a narrow/modest corridor
of returning moisture (low-mid 50s boundary-layer dewpoints) that
will overspread MO/IL through the afternoon. Surface heating in
cloud breaks, continued moisture advection and relatively cool
midlevel temperatures will all contribute to warm sector
destabilization (MLCAPE 500-750 J/kg) through the afternoon across
IL.
Surface-based thunderstorm development will become probable by
early-mid afternoon in a broken band along and just ahead of a
remnant dryline moving from MO into IL, and storms will subsequently
move eastward/northeastward into IN by early tonight before
weakening gradually. The deeper buoyancy profiles will be on the
cyclonic side of the midlevel jet, where 500 mb temperatures will be
< -20 C. Forecast wind profiles suggest supercell potential with
long hodographs (effective bulk shear vectors >50 kt), and
sufficient low-level hodograph curvature/shear for tornado
potential. The primary uncertainty centers of the degree of
low-level moistening/destabilization, and the current forecast
represents a conditional/reasonable worst case scenario. Otherwise,
occasional large hail (1-1.5 inches in diameter) will be possible in
IL this afternoon/evening, and the threat for damaging gusts (60-70
mph) and a couple of tornadoes will persist into IN through early
tonight.
...TN/MS/AL this afternoon/evening...
Boundary-layer dewpoints will slowly increase to the upper 50s/lower
60s ahead of the surface wind shift moving across AR/LA this
afternoon. Forcing for ascent should be sufficient to remove the
cap, allowing some deep convection in a broken band this
afternoon/evening. Buoyancy will be relatively weak compared to the
vertical shear, so it will be difficult to get sustained severe
storms and isolated wind damage will be the most probable threat.
..Thompson/Dean.. 03/19/2025
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