Mesoscale Discussion 496

Issued

May 3, 2021, 2:08 PM CDT (19:08 UTC)

Expired

May 3, 2021, 3:15 PM CDT

In force

67 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

The Lincoln radar (KILX), 97 km from the middle of the area, began a volume at 19:08 UTC, the scan nearest the moment this went out.

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• Severe Thunderstorm Watch 131May 3, 2:45 PM CDT

199 
ACUS11 KWNS 031909
SWOMCD
SPC MCD 031908 
ILZ000-MOZ000-IAZ000-032015-

Mesoscale Discussion 0496
NWS Storm Prediction Center Norman OK
0208 PM CDT Mon May 03 2021

Areas affected...Eastern Missouri into central Illinois

Concerning...Severe potential...Watch likely 

Valid 031908Z - 032015Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms will likely overspread eastern Missouri into
central and northern Illinois over the next several hours. Scattered
strong to severe storms are likely and will support a risk for
damaging wind and hail.

DISCUSSION...Recent visible satellite imagery reveals gradually
clearing skies across western and southern IL ahead of a cold front
draped from central WI southward through western MO. This is also
just ahead of a remnant MCV that is slowly propagating eastward
ahead of the front. Recent RAP mesoanalysis indicates MLCIN is
decreasing across the clearing warm sector where temperatures are
warming into the low 70s/upper 80s and deeper boundary-layer mixing
is eroding remaining inhibition. Insolation, combined with low to
mid 60s dewpoints and mid-level lapse rates approaching 7 C/km, is
supporting MLCAPE values on the order of 1000-1500 J/kg. While the
most favorable air mass is currently limited to eastern MO/western
IL, the warm sector should spread eastward with time as clearing
continues. 

30-45 knots of effective bulk shear nearly orthogonal to the front
and a subtle surface trough extending southward from the MCV (noted
in surface obs across central MO) should support semi-discrete cells
within a broken line along the front. Low-level shear is expected to
gradually increase across the warm sector with ESRH values near 150
m2/s2, which may support a tornado threat - particularly in the
vicinity of the MCV across central IL where low-level flow may be
slightly more backed to the southeast (though confidence in this
potential is low). Regardless, a watch is likely in the coming hours
as convection continues to develop.

..Moore/Grams.. 05/03/2021

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

ATTN...WFO...PAH...LOT...ILX...LSX...DVN...SGF...

LAT...LON   38819228 39879213 40729208 41339111 41458985 41148864
            40428791 39678769 38848792 38268844 38018929 38009046
            38079177 38819228

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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.