Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0740 AM CDT Sun Jun 21 2026
Valid 211300Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
CENTRAL PLAINS INTO THE MID MISSISSIPPI AND LOWER OHIO VALLEYS...
...SUMMARY...
Scattered severe thunderstorms should occur from the central High
Plains into the mid Mississippi and lower Ohio Valleys, mainly this
afternoon into tonight. Large to very large hail, severe/damaging
winds (some 75+ mph), and tornadoes will all be possible. Some
potential for strong tornadoes may develop across parts of Missouri,
Illinois, and Indiana during the afternoon and evening.
...Central Plains to the Mid Mississippi and Lower Ohio Valleys...
An MCS with a convectively augmented parent MCV extends from parts
of central MO into southeast KS/northern OK this morning. The
airmass downstream of this MCS across MO is not particularly
unstable, but greater low-level moisture and related instability is
present across northeast OK and vicinity. Current expectations are
for the MCS/MCV to continue eastward across the mid MS Valley and
Ozarks through the morning while posing an isolated threat for
severe/damaging winds. With time, some re-invigoration of the MCS
appears possible into the lower OH Valley as destabilization occurs
with daytime heating. Trailing outflow from the morning convection
will serve as a focus for additional thunderstorms later today as a
compact/enhanced low-level jet moves eastward from the Ozarks into
the mid MS/lower OH Valleys.
There still appears to be potential for more robust thunderstorm
development this afternoon across these areas along and south of the
outflow boundary/front. Moderate instability will likely develop in
the presence of 30-40 kt of deep-layer shear, which will be
sufficient to support supercells. Enhanced low-level shear will also
be present owing to the eastward-migrating low-level jet. This will
foster a risk for tornadoes with any sustained supercells, and a
strong tornado appears possible. Considered greater tornado
probabilities and a categorical upgrade in a narrow corridor across
parts of MO/IL/IN, but there remains too much uncertainty regarding
sufficient destabilization in the wake of the morning activity. The
severe/damaging wind threat will also increase, with the potential
for multiple clusters to form and track eastward into the lower OH
Valley through the evening and early overnight hours.
Convective development should also occur farther west along/near the
composite outflow boundary/front across the Ozarks into southern
KS/northern OK by peak afternoon heating. Strong instability and
moderate deep-layer shear will likely support updraft organization
and a mix of supercells and multicell clusters. Large to very large
hail should be the primary threat initially, but deep-layer shear
vectors aligned largely parallel to the boundary should foster
convective mergers and an increasing threat for severe/damaging
winds with multiple clusters that should form and spread
east-southeastward across OK and the Ozarks through the evening. At
least an isolated severe wind threat may persist overnight with
southward extent across the southern Plains into AR given the large
degree of buoyancy forecast.
A mid-level shortwave trough over WY this morning will move
east-southeastward towards the central High Plains by this
afternoon. Enhanced westerly flow aloft attendant to this shortwave
trough will overspread the central High Plains through the day. A
convectively reinforced front extends from northwest OK into the
central High Plains, and modest low-level upslope flow is forecast
to the north of this boundary today. Recent short-term guidance
continues to suggest that moderate instability will develop with
filtered daytime heating in the presence of steep mid-level lapse
rates and strong effective bulk shear. Isolated supercells that can
develop in this regime across eastern CO into western NE/KS should
pose mainly a large to isolated very large (2+ inches) hail risk
initially, before some clustering/upscale growth possibly occurs
this evening. Scattered severe/damaging winds would become an
increasing concern if this mode transition occurs, and isolated
significant gusts (75+ mph) appear possible.
..Gleason/Broyles.. 06/21/2026
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