MESOSCALE PRECIPITATION DISCUSSION 0267
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1131 PM EDT WED OCT 02 2013
 
AREAS AFFECTED...EASTERN NE AND WESTERN IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 030330Z - 030630Z
 
SUMMARY...AN EXPANDING AREA OF THUNDERSTORMS ACROSS EASTERN NE IS
BEGINNING TO ENTER WESTERN IA WITH HOURLY RAINFALL RATES OF 2-3
INCHES.  REGIONAL FLASH FLOODING IS CONSIDERED POSSIBLE DESPITE
ITS FORWARD PROGRESSION.

DISCUSSION...AN EXPANDING AREA OF THUNDERSTORMS STRETCHES ACROSS
EASTERN NE AND IS ABOUT TO ENTER WESTERN IA.  RADAR-DERIVED
RAINFALL RATES ARE 2-3 INCHES PER HOUR IN STRONGER CELLS. 
PRECIPITABLE WATER VALUES OF 1.25-1.5 INCHES ARE BETWEEN THE 85TH
AND 90TH PERCENTILES FOR EARLY OCTOBER, WHICH IS AIDING
PRECIPITATION EFFICIENCY.  IT APPEARS THIS SEGMENT OF THE
THUNDERSTORM AREA IS FORWARD PROPAGATING DUE TO WEAKER INFLOW THAN
SEEN ACROSS SOUTHERN NE.  CAPES ARE IN THE NEIGHBORHOOD OF
1000-1500 J/KG, WHICH SHOULD REMAIN PERSISTENT OVERNIGHT.  WHEN
COMBINED WITH LOW-LEVEL INFLOW OF AROUND 25 KTS AND 0-2.5 KM
VERTICAL WIND SHEAR OF AROUND 30 KTS, THERE IS A LOW-END RISK OF
ORGANIZED WET MACROBURST MULTICELLS.

THE THUNDERSTORMS APPEAR TO BE PROGRESSING BETWEEN THAT INDICATED
BY THE CORFIDI VECTORS -- LIGHT SOUTHEAST MOTION -- AND WHAT IS
INDICATED IN THE 850-400 HPA MEAN WINDS -- TOWARDS THE ENE AT 20+
KTS.  IT IS PRESUMED THIS IS PARTIALLY DUE TO AN EASTWARD-MOVING
OUTFLOW BOUNDARY CAUSED BY AN ASSOCIATED LOW-LEVEL COOL POOL.  BY
06Z, VEERING LOW-LEVEL FLOW SHOULD ALLOW CONVECTION ACROSS NE TO
SPEED UP ITS FORWARD PROPAGATION MORE TO THE SOUTHEAST WHICH WOULD
MINIMIZE REGIONAL FLASH FLOODING, WHICH LED TO A THREE HOUR VALID
TIME.

ROTH

ATTN...WFO...DMX...FSD...OAX...GID...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   40899674 41399759 41999696 42399577 42269478 41689487
            41099551 40899674