Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1156 PM CST Mon Feb 26 2024
Valid 271200Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID MS AND LOWER OH VALLEYS INTO THE SOUTHERN GREAT LAKES....
...SUMMARY...
Scattered strong to severe thunderstorms, associated with large hail
(some 2 inches diameter), damaging gusts, and a few tornadoes will
be possible from late this afternoon into the evening and overnight,
from parts of the mid Mississippi Valley to the Ohio Valley and
southern Great Lakes.
...Synopsis...
Low-amplitude, split mid-level flow over much of the central and
western CONUS will gradually consolidate and amplify through the
forecast period, as a northern-stream shortwave trough merges with
strong southwesterly flow from the southern stream. Multiple weak
perturbations embedded within the increasingly strong
southern-stream flow ahead of the main vort max will aid in
deepening a broad surface cyclone along a cold front over the
northern Plains. As the surface low and trailing front advance, warm
advection will draw limited, but sufficient, moisture northward into
the lower OH Valley and Great Lakes. Strong to severe thunderstorms
are possible ahead of the low and along the trailing front through
early Wednesday.
...Mid MS and Lower OH Valley...
Early in the forecast period, isolated to widely scattered
thunderstorms may be ongoing within a strong low-level warm
advection regime over the lower OH Valley. Ahead of the main surge
of deeper surface moisture, these storms are expected to remain
primarily elevated through the mid morning. Elevated buoyancy, steep
lapse rates and sufficient vertical shear for supercells may support
a conditional risk for large hail through mid morning.
Continued warm advection should gradually transport upper 50s to low
60s F surface dewpoints northward into parts of southern and central
IL, IN and western OH by mid afternoon. A diffuse moisture gradient
along a surface pressure trough/weak dryline should become
established across western/central IL into far eastern MO by late
afternoon. Strong surface heating and confluence along this feature
may support isolated convective development by 21-00z across
central/northern IL. At the same time, warm advection along an
expected differential-heating zone near the nose of the returning
surface moisture may allow for scattered thunderstorm development
across portions of northern IN, southern lower MI and northwestern
OH. Model soundings show moderate MLCAPE (1500-2000 J/kg) and strong
effective shear of 40-50 kt favorable for supercells. A prominent
EML for February, with lapse rates of 8 C/km, will favor strong
updrafts with efficient hail growth and a risk for significant hail.
Later in the evening, the approach of the deepening mid-level trough
and surface pressure falls ahead of the surface low across northern
IL will yield increasing mass response across the warm sector. Model
soundings show enlarged low-level hodographs potentially supporting
a few tornadoes and damaging gusts.
As the cold front and low move eastward, additional storm
development is possible along the surface pressure trough and the
surging cold front across portions of far eastern MO and southern
IL. Uncertainty on storm mode and coverage remains fairly high, with
some CAM solutions suggesting more isolated development ahead of the
line, while other show mostly linear growth along the front.
Regardless, these storms should continue eastward overnight across
southern IN, northern KY and into southwestern OH with the potential
for hail and damaging gusts. Should more discrete development occur
and be maintained ahead of the building squall line, increasingly
strong low-level shear (0-1km SRH of 250-400 m2/s2) could support a
risk for tornadoes. The severe threat should gradually diminish into
Wednesday morning as the frontal squall line pushes eastward into
parts of eastern OH and the central Appalachians with decreasing
buoyancy.
..Lyons/Darrow.. 02/27/2024
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