MESOSCALE PRECIPITATION DISCUSSION 0268
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1151 PM EDT WED JUN 24 2015
 
AREAS AFFECTED...AREAS SURROUNDING THE MO/IL/IA BORDER 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 250351Z - 250921Z
 
SUMMARY...THUNDERSTORM ACTIVITY IS EXPECTED TO CONTINUE GROWING IN
SCALE OVERNIGHT.  SINCE THE STORMS ARE MOVING OVER SATURATED
SOILS, FLASH FLOODING IS LIKELY.

DISCUSSION...AN ELONGATING AREA OF THUNDERSTORMS COMPOSED OF
BACKBUILDING AND FORWARD PROPAGATING ELEMENTS IS ENVELOPING
GREATER REAL ESTATE ACROSS SOUTH-CENTRAL IA.  VAD WIND PROFILES
SHOW A BROAD AREA OF 25-40 KT INFLOW AT 850 HPA, ADVECTING IN FROM
A POOL OF STRONG INSTABILITY UNDER A CAP (3500-4500 J/KG MLCAPE). 
PRECIPITABLE WATER VALUES ARE AROUND 2", AT LEAST TWO SIGMAS ABOVE
THE NORM FOR LATE JUNE.  SOME DIRECTIONAL WIND SHEAR EXISTS IN
THIS REGION, WHICH COMBINED WITH THE STRONG INSTABILITY IS LEADING
TO SOME FORWARD PROPAGATING ELEMENTS ALONG ITS EAST/SOUTHEAST
EDGE.  THE MEAN PROPAGATION IS EXPECTED TO BE EAST-SOUTHEAST AT 30
KT BASED ON THE 18Z GFS AND TAKING THE ALIGNMENT OF THE 1000-500
HPA THICKNESS AND MLCAPE GRADIENTS INTO ACCOUNT.

MUCH OF THE AVAILABLE MESOSCALE QPF GUIDANCE APPEARS TOO FAR NORTH
WITH THE EXPECTED HEAVY RAIN AXIS BASED ON THE CURRENT AND
EXPECTED BOUNDARY LAYER MOISTURE CONVERGENCE FROM THE 01Z RAP.  AT
THIS TIME, A SLIGHTLY NORTHEAST ADJUSTED 02Z HRRR APPEARS TO BE
THE BEST BET.  INFLOW AT 850 HPA IS EXPECTED TO NEAR 50 KTS
OVERNIGHT, 15-20 KTS ABOVE THE MEAN 850-400 HPA WIND, AND SHOULD
SLOWLY BECOME MOST WESTERLY WITH TIME.  THIS WOULD CAUSE SOME
EAST-SOUTHEAST TO SOUTHEAST SHIFT IN THE BACKBUILDING REGION
ACROSS IA.  THIS SHOULD ALLOW FOR PRECIPITATION EFFICIENCY, WITH
HOURLY RAIN RATES UP TO 2.5" ANTICIPATED, HIGHER IN REGIONS OF
PROLONGED CELL TRAINING, CELL MERGERS, AND MCV DEVELOPMENT.  LUCAS
IA RECEIVED 1.75" IN 20 MINUTES, INDICATING THAT THE MCS IS VERY
EFFICIENT RAINFALL PRODUCTION-WISE.  THERE ARE NO MAJOR SHORTWAVES
ALOFT THAT WOULD POTENTIALLY DISRUPT THE BACKBUILDING ACROSS IA,
WHICH INCREASES THE OVERALL FLASH FLOOD THREAT.  THE MESOSCALE
GUIDANCE GENERALLY ADVERTISES LOCAL AMOUNTS IN THE 4-6" RANGE. 
THROW INTO THE MIX THAT THIS AREA HAS RECEIVED 8-10" OF RAIN OVER
THE PAST 30 DAYS PER SOUTHERN REGION PRECIPITATION ESTIMATES,
FLASH FLOODING IS CONSIDERED LIKELY OVER SATURATED SOILS.

ROTH

ATTN...WFO...DMX...DVN...EAX...ILX...LSX...OAX...

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

LAT...LON   42459408 42179091 40938907 39978876 38948919 
            38509043 40279283 41149412 42009545