AREAS AFFECTED...NERN IL...NRN IND...SWRN LOWER MI
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 282230Z - 290000Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...AN AT LEAST ISOLATED SVR THREAT MAY MATERIALIZE ACROSS
PARTS OF NERN IL/NRN IND/SWRN LOWER MI. CONVECTIVE TRENDS WILL
CONTINUE TO BE MONITORED...AND A WW IS POSSIBLE IF A MORE WIDESPREAD
SVR THREAT APPEARS TO ENSUE.
DISCUSSION...ISOLATED CONVECTION IS DEVELOPING INVOF A SFC FRONT AND
NEARBY WIND-SHIFT AXES...ENHANCED BY LOCALIZED LAKE-BREEZE
CIRCULATIONS NEAR AND NORTH OF THE CHICAGO AREA. THE AREAS OF
GREATEST CONCERN FOR POSSIBLY SVR CONVECTION DURING THE NEXT HOUR OR
TWO INCLUDE KANE COUNTY EWD TO COOK COUNTY INTO SRN LAKE
MICHIGAN...WITH POTENTIAL IMPACTS TO THE CHICAGO AREA BETWEEN 2300
AND 2330 UTC.
THE CONVECTION APPEARS TO BE COLOCATED WITH THE WARM SIDE OF A
700-MB THERMAL GRADIENT. WHILE HOT INLAND SFC TEMPERATURES AMIDST
LOWER/MIDDLE 70S DEWPOINTS ARE SUPPORTING EXTREME
INSTABILITY...STRONG INHIBITION SOUTH OF THE 700-MB TEMPERATURE
GRADIENT OWING TO A PRONOUNCED WARM-LAYER ALOFT -- 700-MB TEMPS IN
EXCESS OF 16C -- YIELD UNCERTAINTY WITH REGARD TO THE FUTURE
EVOLUTION OF ONGOING CONVECTION. FURTHERMORE...THE ONLY GLANCING
INFLUENCE OF A MID-LEVEL SHORTWAVE TROUGH AND ASSOCIATED HEIGHT
FALLS/ASCENT SHOULD PROVIDE ONLY MINIMAL REDUCTION TO ONGOING CINH.
REGARDLESS...THERE IS SOME CONCERN FOR A LOCALIZED SVR-WIND THREAT
GIVEN SFC DEWPOINT DEPRESSIONS IN EXCESS OF 20F AND DCAPE VALUES IN
AOA 1300 J/KG...AS WLY/NWLY MID-LEVEL FLOW STEERS CONVECTION FROM
NERN IL INTO SWRN LOWER MI AND NRN IND. IF STORMS APPEAR TO SHOW
SIGNS OF GROWING UPSCALE INTO A CONVECTIVE COMPLEX WITH A MORE
WIDESPREAD SVR THREAT...A WW MAY BE NEEDED.
..COHEN/HART.. 06/28/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...IWX...GRR...LOT...
LAT...LON 42078508 41738528 41388615 41278783 41658893 42078911
42318826 42428749 42558686 42688579 42558527 42078508
