MD 1159 CONCERNING SEVERE THUNDERSTORM WATCH 331… FOR PORTIONS CENTRAL/NRN IL…SRN/ERN IA…LM…EXTREME NERN MO…NWRN INDIANA.
MESOSCALE DISCUSSION 1159
NWS STORM PREDICTION CENTER NORMAN OK
0127 AM CDT WED JUL 06 2016
AREAS AFFECTED...PORTIONS CENTRAL/NRN IL...SRN/ERN IA...LM...EXTREME
NERN MO...NWRN INDIANA.
CONCERNING...SEVERE THUNDERSTORM WATCH 331...
VALID 060627Z - 060830Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 331
CONTINUES.
SUMMARY...ALTHOUGH OVERALL SEVERE POTENTIAL WITH ONGOING CONVECTIVE
SYSTEMS MAY RAMP DOWN GRADUALLY THROUGH PRE-DAWN HOURS...WE EXPECT
DAMAGING-WIND RISK TO PERSIST LONG AND FAR ENOUGH OUT OF EXISTING
WATCH AREAS THAT A NEW WATCH IS LIKELY TO BE NEEDED IN SHORTER
TERM...PRIMARILY S OF WW 331.
DISCUSSION...LEADING/LARGEST MCS WAS EVIDENT AT 0615Z ALONG ARC
EXTENDING NEAR GRB...JVL...WTI. THIS COMPLEX HAS BEEN DECAYING FROM
N-S AS IT ENCOUNTERS PROGRESSIVELY MORE STABLE BOUNDARY-LAYER AIR
RELATED TO COMBINATION OF BOTH NOCTURNAL/DIABATIC SFC COOLING AND
WRN FRINGES OF MARINE-LAYER SEEPAGE FROM LM. THIS PROCESS SHOULD
CONTINUE...CAUSING CONTINUED EROSION OF DEEPEST/HIGH-REFLECTIVITY
STRUCTURES SWD INVOF LAKESHORE...AND CORRESPONDING N-S-DIRECTED
WARMING OF IR CLOUD TOPS ALREADY NOTED OVER ERN WI. STILL...STG
PRESSURE/THETAE PERTURBATIONS ASSOCIATED WITH THIS COMPLEX MAY FORCE
AT LEAST MRGL SVR POTENTIAL ONTO SWRN PORTIONS OF LAKESHORE ACROSS
WI/IL...AND ADJOINING PARTS OF LM. GIVEN THIS FACTOR...WW 331 HAS
BEEN EXTENDED TO IMMEDIATE SHORELINE AREA IN WI. REMAINDER OF MCS
SHOULD PUSH SEWD INTO MORE OF NRN AND EVENTUALLY CENTRAL IL.
PROSPECTIVE INFLOW-LAYER AIR MASS IS CHARACTERIZED BY RICH LOW-LEVEL
MOISTURE THAT IS KEEPING PACE SLOW FOR DIABATIC SFC COOLING...WITH
MUCAPE RANGING FROM 1000 J/KG IN CHICAGOLAND AREA TO OVER 4000 J/KG
OVER SERN IA/NWRN IL.
OUTFLOW BOUNDARY FROM LEADING MCS TRAILS SWWD/WWD ACROSS CENTRAL IA
NE OF DSM...WHERE IT IS BEING OVERTAKEN BY LONG-LIVED..SMALLER BUT
STILL STG/SVR TSTM COMPLEX WITH HISTORY OF DAMAGING WINDS. THAT MCS
IS EXPECTED TO FOCUS PREFERENTIALLY INTO OPTIMAL THETAE ALONG AND S
OF STILL-PROGRESSIVE OUTFLOW BOUNDARY THAT WILL REORIENT WNW-ESE
WITH TIME. ALTHOUGH WW 331 HAS BEEN EXTENDED S OVER PARTS OF SERN
IA TO COVER SHORT-FUSED THREAT...ASSOCIATED LIFT/CONVERGENCE AND
PROPAGATION SHOULD REDIRECT ASSOCIATED SVR POTENTIAL STILL FARTHER
SEWD INTO PORTIONS SERN IA/NWRN IL NOT PRESENTLY IN WWS.
..EDWARDS.. 07/06/2016
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...GRB...LOT...ILX...MKX...LSX...DVN...DMX...EAX...
LAT...LON 41399467 41809366 42309329 42449321 42159140 42318999
43008894 43928816 43808718 42618726 41148722 40588764
40178852 40168992 40159098 40429229 40999413 41399467
from SPC Mesoscale Discussions http://bit.ly/1lsATBV
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