ACUS11 KWNS 241925
SWOMCD
MESOSCALE DISCUSSION 1387
NWS STORM PREDICTION CENTER NORMAN OK
0225 PM CDT SUN JUL 24 2016
AREAS AFFECTED...PORTIONS OF SE WI...SWRN LOWER MI...NERN IL...NRN
INDIANA...SRN LAKE MI
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 241925Z - 242200Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...THE AREA IS BEING MONITORED FOR INCREASING SVR-TSTM
POTENTIAL. DAMAGING WINDS AND LARGE HAIL WILL BE POSSIBLE. WHILE
UNCERTAINTY REMAINS REGARDING THE CONVECTIVE EVOLUTION AND TIMING OF
MORE SUBSTANTIAL SVR RISK...THE ISSUANCE OF A SVR TSTM WATCH IS
POSSIBLE.
DISCUSSION...SFC MESOANALYSIS PLACES A WEAK COLD FRONT ARCHING FROM
NERN WI TO SERN IA...WITH A RESIDUAL OUTFLOW BOUNDARY EXTENDING FROM
SERN WI THROUGH SRN LAKE MI AND INTO NWRN OH. THE AIR MASS AHEAD OF
THE COLD FRONT...AND S OF THE OUTFLOW BOUNDARY...HAS BECOME
EXTREMELY UNSTABLE. WITH VERY RICH LOW-LEVEL MOISTURE -- E.G. SFC
DEWPOINTS WELL INTO THE 70S...TO AROUND 80F IN NRN IL -- DIABATIC
HEATING OF THE SFC LAYER IS SUPPORTING MLCAPE UPWARDS OF AROUND
4500-5000 J/KG S OF THE OUTFLOW BOUNDARY. WEAKER BUOYANCY EXISTS
FARTHER N FROM PARTS OF SWRN LOWER MI TO E-CNTRL WI -- WHERE
AIR-MASS RECOVERY IS ONGOING IN THE WAKE OF EARLIER CONVECTION.
VISIBLE SATELLITE LOOPS SUGGEST THAT PRE-FRONTAL STRATOCUMULUS
CLOUDS ARE FRAGMENTING FROM SRN WI TO NRN IL...GIVING WAY TOO MORE
CELLULAR-CUMULUS STRUCTURES. FURTHERMORE....INITIAL RADAR RETURNS
ARE BECOMING APPARENT OVER SERN WI...WHERE LITTLE MLCINH REMAINS
AMIDST THE VERY MOIST BOUNDARY LAYER. THIS ACTIVITY IS DEVELOPING
AMIDST NEAR-NEUTRAL LARGER-SCALE VERTICAL MOTION FIELDS...AS
WATER-VAPOR LOOPS IMPLY A DEARTH OF ASCENT ACROSS THE AREA...AND
LOW-LEVEL CONVERGENCE IS WEAK. NEVERTHELESS...SFC OBS IMPLY A
CONFLUENCE AXIS EXTENDING FROM W-CNTRL IL INTO SERN WI -- ALONG
WHICH CONVECTION MAY CONTINUE TO DEVELOP GIVEN THE LACKING MLCINH
AIDED BY THE VERY MOIST BOUNDARY LAYER.
ULTIMATELY...THERE IS UNCERTAINTY REGARDING THE DEVELOPMENT OF
CONVECTION THROUGH MID/LATE-AFTERNOON GIVEN THE LIMITED ASCENT.
HOWEVER...GIVEN THE LARGE DEGREE OF BUOYANCY...AND AT LEAST SOME
LOW-LEVEL LIFT LARGELY MODULATED BY MODIFYING OUTFLOW AND LOCALLY
CONCENTRATED ALONG THE CONFLUENCE AXIS...SUSTAINED TSTM DEVELOPMENT
MAY OCCUR -- ESPECIALLY FOLLOWING REPEATED CONVECTIVE ATTEMPTS. THIS
INITIAL ACTIVITY IS MOST PROBABLE FROM SERN WI TO NERN IL INCLUDING
CHICAGO TO SWRN LOWER MI...WITH THIS ACTIVITY SPREADING SEWD THROUGH
THE EVENING HOURS -- NEAR AND S OF THE OUTFLOW BOUNDARY. THE
SUBSTANTIAL DEGREE OF BUOYANCY SHOULD SUPPORT THE POTENTIAL FOR SVR
WIND/HAIL. THE SVR-WIND RISK WOULD LOCALLY INCREASE WITH CASES OF
MESOSCALE CONVECTIVE CLUSTERING/COLD POOL AMALGAMATION...THOUGH DEEP
SHEAR SHOULD REMAIN MODEST -- E.G. EFFECTIVE SHEAR AROUND 20-30 KT.
..COHEN/WEISS.. 07/24/2016
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...IWX...GRR...IND...LOT...MKX...
LAT...LON 40878607 40628728 41228865 42098924 43128863 42968698
42438564 41558546 40878607
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