[MCD] SWOMCD

[MCD at goshenarc.org]

ACUS11 KWNS 201632
SWOMCD
SPC MCD 201631 
ILZ000-IAZ000-201900-

MESOSCALE DISCUSSION 0772
NWS STORM PREDICTION CENTER NORMAN OK
1131 AM CDT THU MAY 20 2004

AREAS AFFECTED...CNTRL/SRN IA...PARTS OF NW IL

CONCERNING...SEVERE THUNDERSTORM POTENTIAL 

VALID 201631Z - 201900Z

TRENDS ARE BEING MONITORED FOR INCREASING SEVERE THREAT AND WW. 
INCREASING CONVECTIVE DEVELOPMENT IS ONGOING...BUT ONSET OF
SURFACE-BASED ACTIVITY STILL APPEARS TO BE SEVERAL HOURS AWAY.

INCREASING CONVECTIVE DEVELOPMENT IS EVIDENT IN LATEST VISIBLE
SATELLITE AND RADAR IMAGERY...IN BROAD ANTICYCLONIC ARC FROM PARTS
OF NORTHERN KANSAS/SOUTHERN NEBRASKA THROUGH CENTRAL IOWA.  ACTIVITY
APPEARS TO BE BASED ABOVE CAPPING INVERSION...IN ZONE OF MOIST
ISENTROPIC ASCENT ASSOCIATED WITH LOWER/MID TROPOSPHERIC JET STREAK
NOW PROGRESSING INTO CREST OF SUBTROPICAL RIDGE.  MODELS SUGGEST
THIS FEATURE WILL PROGRESS FROM THE VICINITY OF THE KANSAS/NEBRASKA
BORDER THROUGH AREAS JUST NORTH OF THE MISSOURI/IOWA BORDER THIS
AFTERNOON.

CONSIDERABLE UNCERTAINTY EXISTS ABOUT STRENGTH OF CAPE FOR MOIST
MID-LEVEL PARCELS.  HOWEVER...MID-LEVEL LAPSE RATES ARE QUITE STEEP
ON NORTHERN PERIPHERY OF ELEVATED MIXED LAYER...AND INSTABILITY MAY
BE SUFFICIENT FOR SOME HAIL IN STRONGER CELLS DEVELOPING WITHIN NEXT
HOUR OR TWO.  

CLOSER TO THE 20-21Z TIME FRAME...MODELS SUGGEST MID-LEVEL UPWARD
VERTICAL MOTION FIELD WILL WEAKEN CAP ALONG/AHEAD OF SURFACE FRONT
ACROSS CENTRAL IOWA...PERHAPS AIDED BY EVAPORATIVE COOLING BELOW
MID-LEVEL BASED CONVECTION.  AS THIS OCCURS...POTENTIAL FOR MORE
VIGOROUS SURFACE-BASED THUNDERSTORM ACTIVITY WILL INCREASE.  ONCE
THIS INITIATES...DEVELOPMENT WILL BE RAPID AS BOUNDARY LAYER IS VERY
MOIST WITH 70F+ SURFACE DEW POINTS.  ADDITIONAL SURFACE HEATING
LIKELY WILL YIELD MEAN MIXED LAYER CAPE UP TO 3000 J/KG. 
GIVEN MAGNITUDE OF INSTABILITY...VERTICAL SHEAR PROFILES BENEATH
MID-LEVEL JET WILL BE SUPPORTIVE OF UPDRAFT ROTATION...ENHANCING
POTENTIAL FOR VERY LARGE HAIL.

..KERR.. 05/20/2004

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...ILX...DVN...ARX...DMX...

42419434 42759178 42348998 40798988 40669145 40989454 

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