[LeArc] MESOSCALE DISCUSSION 1751

[Duane Whittingham]

MESOSCALE DISCUSSION 1751
NWS STORM PREDICTION CENTER NORMAN OK
0101 PM CDT WED JUL 21 2004

AREAS AFFECTED...SERN IA INTO NRN IL

CONCERNING...SEVERE THUNDERSTORM WATCH <../watch/ww0661.htm>661...

VALID 211801Z - 211930Z

SO FAR...ORGANIZED TSTMS HAVE NOT DEVELOPED AS PLANNED...BUT SHOULD 
INCREASE THIS AFTERNOON.  ENVIRONMENT IS STILL CONDUCIVE TO A BOW ECHO 
SITUATION WITH DAMAGING WIND THE PRIMARY THREAT.

18Z DAVENPORT SOUNDING SHOWED A WARM LAYER IN THE H85-H7 LAYER AND IS 
LIKELY THE MAIN INHIBITING FACTOR IN SUSTAINED SURFACE BASED TSTM 
DEVELOPMENT THUS FAR.  MODIFYING THE SOUNDING FOR CONDITIONS
DOWNSTREAM ACROSS NRN ILL WITH 85/77 STILL INDICATES ABOUT 75 J/KG 
INHIBITION.  CONTINUED HEATING...HOWEVER...AND INCREASING CONVERGENCE ALONG 
W-E ORIENTED OUTFLOW BOUNDARY WILL LIKELY LEAD TO ADDITIONAL TSTM 
DEVELOPMENT/INTENSIFICATION ACROSS EXTREME SERN IA
OR NWRN IL THIS AFTERNOON.

WIND FIELDS REMAIN VERY FAVORABLE FOR BOW ECHO FORMATION.  DAVENPORT 
SOUNDING SHOWED BETTER THAN 30 KTS OF UNIDIRECTIONAL FLOW ABOVE 2 KM 
AGL.  AS STORMS DEVELOP AND BECOME ALIGNED WITH THE WLY SHEAR VECTORS...A 
BOW ECHO IS LIKELY TO EVOLVE AND TRACK EWD ACROSS NRN IL...NRN IND AND 
EXTREME SRN LOWER MI THROUGH LATE AFTERNOON.
    DAMAGING WINDS WILL BE THE PRIMARY THREAT WITH SOME GREATER THAN 70 KT 
GUSTS POSSIBLE.  HAIL COULD ALSO OCCUR.

AS THE SITUATION EVOLVES...WW MAY NEED TO BE REALIGNED/REISSUED FOR THE 
AREA AND DOWNSTREAM.

..RACY.. 07/21/2004


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