SPC MD 1541

MD 1541 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF EASTERN ILLINOIS AND INDIANA

Mesoscale Discussion 1541
NWS Storm Prediction Center Norman OK
1241 PM CDT Mon Aug 21 2017

Areas affected...Portions of eastern Illinois and Indiana

Concerning...Severe potential...Watch unlikely 

Valid 211741Z - 211915Z

Probability of Watch Issuance...20 percent

SUMMARY...Scattered thunderstorms will further develop across the
region this afternoon. Isolated instances of large hail and damaging
winds will be possible. However, the threat should remain limited
enough to preclude watch issuance.

DISCUSSION...Visible satellite imagery depicts an outflow boundary
extending from north of St. Louis eastward to west-central Indiana
early this afternoon. Ample heating and rich low-level moisture
ahead of this boundary have fostered MLCAPE values upwards of
2000-2500 J/kg, and more robust convection has initiated along the
boundary, with a recent 50-kt gust in Coles County, IL. VWP data and
forecast soundings depict relatively modest flow in low/mid levels;
however, stronger west/southwesterly upper-level flow should promote
occasional updraft organization. Therefore, storms may be capable of
isolated damaging winds and large hail through the afternoon hours.
Unidirectional deep-layer flow, oriented parallel to the outflow
boundary, suggests more linear modes will become dominant later this
afternoon, with the threat transitioning to primarily gusty,
damaging winds. A lack of greater storm organization will likely
preclude watch issuance, though.

..Picca/Grams.. 08/21/2017

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

ATTN...WFO...ILN...IWX...IND...ILX...

LAT...LON   39268866 40328703 41008624 41138529 40668487 39768491
            39198630 38638786 38688841 39058870 39268866 

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