SPC MD 1991

SPC MD 1991


Mesoscale Discussion 1991
NWS Storm Prediction Center Norman OK
1113 AM CDT Mon Aug 14 2023

Areas affected…Northeast Illinois into northwest Indiana

Concerning…Severe potential…Watch unlikely

Valid 141613Z – 141815Z

Probability of Watch Issuance…5 percent

SUMMARY…Thunderstorms moving into northeast Illinois and northwest
Indiana through the early afternoon may pose a brief tornado risk.
Watch issuance is not expected.

DISCUSSION…16 UTC surface analysis shows thunderstorms ongoing
just ahead of a cold front and to the south of a warm frontal
boundary draped across northern IL. The viable warm sector for these
storms will continue to shrink through early afternoon as the front
migrates east. Residual cloud cover has largely muted daytime
heating so far with temperatures warming into the low/mid 70s only
across far northeast IL into northwest IN where cloud breaks are
noted in visible imagery. Though still limited, surface-based
buoyancy will likely be maximized (possibly as high as 500 J/kg) in
this pocket over the coming hours, and may support some
intensification of ongoing convection and/or new thunderstorms that
develop along the cold front. Deep-layer shear vectors and storm
motions nearly orthogonal to the cold front will favor discrete
cells. While winds above 4 km are fairly strong (40+ knots noted in
recent KLOT VWP observations), low-level flow will likely remain
fairly weak. Nonetheless, an instance of large hail or two appears
plausible, and south/southeasterly flow in the 1-2 km layer may
support adequate low-level helicity for a brief tornado through the
early afternoon hours. Given the low-confidence and
spatially-limited nature of the threat, watch issuance is not

..Moore/Hart.. 08/14/2023

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


LAT…LON 40108783 40518839 41158884 41698921 41848923 42128897
42158778 41898759 41648734 41708688 41398672 40868667
40448684 40148711 40138726 40108755 40108783

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