Mesoscale Discussion – outlook for possible severe storm development this Friday afternoon/evening

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The National Storm Prediction Center has issued a Mesoscale Discussion indicating the possibility of a severe weather and the potential for a Watch issuance this afternoon over central Illinois into central Indiana including a portion of the Chicago area south of Interstate-80 (outlined escalloped area on the highlighted map). With a shower/thunderstorm complex moving east across a warm front during the peak-heating time of the day (temperatures reaching the lower 80s and dew points in the 60s) instability will be increasing this afternoon and continue into the early evening.

Below is the discussion issued by the National Storm Prediction Center…

Mesoscale Discussion 0845

NWS Storm Prediction Center Norman OK

0125 PM CDT Fri May 26 2017


Areas affected…Central and eastern Illinois and far western



Concerning…Severe potential…Watch possible


Valid 261825Z – 262100Z


Probability of Watch Issuance…60 percent


SUMMARY…An area of convection over western Illinois will gradually

intensify while moving eastward into the discussion area.  A WW will

be considered around/just after 20Z.


DISCUSSION…Convection over western Illinois is moving eastward

along and just north of a subjectively analyzed surface boundary

lifting slowly northward across central/eastern Illinois.  Along and

south of this boundary, weak to moderate instability has developed

in response to warming surface temperatures (nearing 80F) and low to

mid-60s dewpoints.  This warm front will continue to lift northward

slowly during the day, and the attendant increase of instability and

lift associated with an approaching remnant mesoscale convective

vortex over northwestern Illinois will foster scattered

thunderstorms capable of hail and damaging wind gusts.  A few

tornadoes will also be possible owing to backed surface flow in

vicinity of the lifting warm front/surface boundary especially if

convection can maintain a favorable (cellular) storm mode.