Mesoscale Discussion 621

Issued

Apr 30, 2025, 2:40 PM CDT (19:40 UTC)

Expired

Apr 30, 2025, 4:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The St Louis radar (KLSX), 96 km from the middle of the area, began a volume at 19:42 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Tornado Watch 200Apr 30, 4:40 PM CDT

138 
ACUS11 KWNS 301941
SWOMCD
SPC MCD 301940 
ILZ000-MOZ000-302145-

Mesoscale Discussion 0621
NWS Storm Prediction Center Norman OK
0240 PM CDT Wed Apr 30 2025

Areas affected...East-central Missouri into southern Illinois

Concerning...Severe potential...Watch possible 

Valid 301940Z - 302145Z

Probability of Watch Issuance...40 percent

SUMMARY...A few storms are possible along an outflow boundary. All
severe hazards would be possible. A watch is uncertain in the short
term, but issuance is possible this afternoon depending on
observational trends.

DISCUSSION...Airmass modification after earlier convection has been
evident over the past couple of hours in central Missouri and
southern Illinois. The primary outflow boundary is situated just
south of St. Louis and extends into far southern Illinois and
southern Indiana. Dewpoints south of the boundary have increased to
upper 60s F except for parts of southeastern Missouri which has only
recovered into the low 60s F. North of the outflow boundary, stable
billow clouds remain. However, very near the boundary temperatures
and dewpoints have increased and at least some MLCIN has been
removed and convection has begun to slowly deepen.

With 40 kts of effective shear (more favorably oriented across the
boundary on its western half), supercells would be expected if
storms develop. Large hail and damaging winds would be possible. A
tornado or two would also be possible for storms interacting with
the more backed easterly/southeasterly winds on the cooler side of
the boundary. Being in the wake of an earlier MCV, forcing for
ascent will be nebulous and will depend on heating/destabilization
along the outflow. Trends will continue to be monitored. A watch is
possible this afternoon.

..Wendt/Hart.. 04/30/2025

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...PAH...ILX...LSX...

LAT...LON   38359140 38649151 39179104 39229055 38878972 38828868
            38808815 38618795 38168806 37928814 37538862 37558986
            38359140 

MOST PROBABLE PEAK TORNADO INTENSITY...85-115 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN

Mesoscale Discussions in Illinois, 2025Mesoscale Discussions in Missouri, 2025Every mesoscale discussion in 2025

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.