Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Sun Jun 21 2026
Valid 212000Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE CENTRAL HIGH PLAINS TO THE 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 Illinois,
and Indiana during the afternoon and evening.
...20z Update Mid MS Valley and lower OH Valley...
Minimal changes were made to the prior outlook given the latest
observational trends. Several clusters of strong thunderstorms are
ongoing ahead of an MCV across the mid MS Valley. An observed messy
convective mode should persist with a mix of bowing structures and
transient supercells likely ahead of the MCV, and near the effective
warm front from eastern IL into IN. Additional storm development is
also possible behind the MCV along the remnant boundary into MO and
eastern KS. This will support a risk for damaging gusts and perhaps
a couple of tornadoes where low-level flow is backed and hodographs
are larger. Eventually upscale growth into one or more bowing
clusters is likely later this evening/overnight into the OH valley
with a continued risk for damaging gusts and embedded tornadoes.
...KS/OK this evening/tonight...
Severe storm development appears probable along the modified
trailing outflow across northwest OK and southwest KS this afternoon
into this evening. Sufficient vertical shear exists for supercells
and organized clusters. With large buoyancy and steep low/mid-level
lapse rates, large hail is likely with these strong updrafts. A
brief tornado or two is also possible, owing to storm interactions
and ambient vertical vorticity along the outflow boundary.
Damaging wind potential will likely increase with storm
consolidation, though the more cellular initial mode suggests this
maybe somewhat gradual. These storms, and additional convection
originating further north from the central High Plains, should
persist overnight into central and southern OK, reaching the Red
River Valley by 12z tomorrow morning with isolated severe potential.
..Lyons.. 06/21/2026
.PREV DISCUSSION... /ISSUED 1110 AM CDT Sun Jun 21 2026/
...MO/IL/IN/KY...
A long-lived band of thunderstorms currently extends from
east-central MO into southwest MO/northeast OK. This activity is
tracking into a region of increasingly warm/moist air where
dewpoints are rising to near 70F and breaks in the clouds are
contributing to moderate CAPE values. All CAM guidance suggests
that storms along the line will intensify this afternoon and track
eastward across southern IL/southern IN and northern KY. Low-level
shear is quite strong, but somewhat veered. This increases
uncertainty of storm mode between discrete supercells or bowing
structures. It appears there will be a period of risk early in the
event for tornadic supercells, followed by multiple linear storm
segments capable of damaging wind gusts. Storms may remain severe
as far east as southern OH and eastern KY overnight. Refer to MD
#1228 for further short-term details.
...MO/KS/OK/AR...
In the wake of the aforementioned convection, an outflow boundary
extends southwestward into central OK. Rapid clearing is occurring
north of the boundary, where residual moisture and steep lapse rates
will quickly destabilize the area. Scattered thunderstorms are
expected to form by late afternoon in this zone and track slowly
southeastward. Sufficient deep-layer shear and high CAPE will
promote the risk of a few supercells capable of large hail and
damaging winds. A tornado or two might also occur.
...NE/CO/KS...
Low clouds are eroding across the NE Panhandle southward into
eastern CO/western KS, where rapid afternoon destabilization should
occur. A weak shortwave trough over eastern WY will rotate into the
region this afternoon, helping to initiate scattered thunderstorms.
Supercells capable of very large hail appear possible, tracking
southeastward across the risk area through mid-evening.
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