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MD 1228 CONCERNING SEVERE POTENTIAL…WATCH POSSIBLE FOR SOUTHERN ILLINOIS…MUCH OF SOUTHEASTERN MISSOURI…ADJACENT NORTHERN ARKANSAS
Mesoscale Discussion 1228
NWS Storm Prediction Center Norman OK
1006 AM CDT Sun Jun 21 2026
Areas affected...southern Illinois...much of southeastern
Missouri...adjacent northern Arkansas
Concerning...Severe potential...Watch possible
Valid 211506Z - 211700Z
Probability of Watch Issuance...40 percent
SUMMARY...Thunderstorm development may slowly intensify through
early afternoon, accompanied by increasing strong to severe wind
gusts and a risk for tornadoes. A severe weather watch will
probably be needed at some point, though how soon remains uncertain.
DISCUSSION...Convective development persists with a pair of remnant
mesoscale convective vortices migrating eastward, within the leading
edge of weak larger-scale mid-level troughing spreading across the
lower Missouri/middle Mississippi Valley region. One vortex remains
a bit better defined and is in the process of migrating across
northeastern Missouri into west central Illinois. The other appears
to be slowly migrating eastward to the north of Springfield, MO. A
belt of 30+ kt deep-layer southwesterly mean flow is accompanying
these perturbation, and appears to include wind speeds on the order
of 30-50 kt in the 850-500 mb layer.
Associated shear likely has been contributing to the occasional
evolution of meso-gamma scale circulations along the gust front of
otherwise still modest thunderstorm development now advancing
into/across the I-44 corridor of southwestern Missouri. However,
low-level moistening and boundary-layer warming along and north of a
weakening frontal zone extending eastward ahead of activity are
contributing to substantive boundary layer destabilization across
southeastern Missouri, as far north as the Greater St. Louis area,
into the lower Ohio Valley. As this proceeds, and develops further
northward through portions of central Illinois during the next few
hours, increasing unstable updraft inflow probably will contribute
to at least a gradual intensification of storms with increasing
severe weather potential. This may include developing cyclonic
circulations with potential to produce strong to severe surface
gusts and the risk for tornadoes.
..Kerr/Hart.. 06/21/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PAH...ILX...MEG...LSX...LZK...SGF...TSA...
LAT...LON 36709359 37529259 38199178 38709116 39219032 39528932
39688774 38128830 36558965 36019142 36339326 36709359
MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN