ACUS11 KWNS 172005
SWOMCD
SPC MCD 172004=20
ILZ000-MOZ000-IAZ000-172100-

Mesoscale Discussion 0477
NWS Storm Prediction Center Norman OK
0304 PM CDT Fri Apr 17 2026

Areas affected...portions of eastern Missouri into western Illinois

Concerning...Severe potential...Watch likely=20

Valid 172004Z - 172100Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms developing across the eastern portions of
Missouri may bring the potential for all severe hazards this
afternoon/evening. Watch issuance may be needed soon.

DISCUSSION...Scattered thunderstorm development is ongoing across
portions of eastern Missouri along a weak confluence zone. Storms
have been somewhat slow to strengthen thus far (perhaps owing to a
lingering warm layer around 750 mb). While stronger upper-level
forcing remains displaced to the north and west, forecast soundings
indicate isolation will continue to erode any lingering inhibition.
While some uncertainty remains regarding convective intensification,
the environment ahead of these storms is conditionally favorable for supercells.=20

Surface temperatures in the low/mid-80s F with dewpoints in the
mid-60s are contributing to 2000-3000 J/kg MLCAPE. 35-45 kts of
effective bulk shear will support supercell structures with
thunderstorms that can become more well established. Steep mid-level
lapse rates and elongated hodographs sampled by the 18z TOP/DVN
observed soundings and recent ACARS profiles from STL will support
the potential for large hail of 1-2" in diameter. Steep low-level
lapse rates (8+ C/km) will also promote strong downdraft wind gusts
with thunderstorms. With time, some increase in tornado risk appears
possible owing to a strengthening of the nocturnal low-level jet.
Convective trends will continue to be monitored, and watch issuance
may be needed soon.

..Chalmers/Mosier.. 04/17/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!6WfCMn3A-S5lkQ5kC1ZqmNOhgnxn9lQLZZsVm5uotW8lwVu_fsBY9E9jLr0_cG4Hfh0drufDf= 9EdUe1s_alCdMvYjWc$ for graphic product...

ATTN...WFO...ILX...LSX...DVN...

LAT...LON 38259145 38449196 38919229 39449222 40129204 40589127
40519028 40148955 39698896 39038870 38488917 38058994
38169075 38259145=20

MOST PROBABLE PEAK TORNADO INTENSITY...100-130 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN


=3D =3D =3D
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