MESOSCALE PRECIPITATION DISCUSSION 0301...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 AM EDT WED AUG 20 2014
 
CORRECTED FOR PW VALUE SOURCES

AREAS AFFECTED...MID MISSOURI-VALLEY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 200358Z - 200958Z
 
SUMMARY...A NORTHWEST-SOUTHEAST ORIENTED THUNDERSTORM BAND IS
EXPECTED TO FORM NEAR THE COMMON BORDERS OF NE/IA AND KS/MO
BETWEEN 05-08Z, WITH EMBEDDED CONVECTION THAT COULD BACKBUILD
AND/OR TRAIN FOR A FEW HOURS THEREAFTER.  FLASH FLOODING IS
CONSIDERED POSSIBLE.

DISCUSSION...A WEAK MESOSCALE FRONTAL WAVE ACROSS SOUTHWEST NE WAS
SEEN IN THE 03Z OBSERVATIONS, WITH A WARM FRONTAL FEATURE
EXTENDING SOUTHEAST THROUGH KS INTO NORTHEAST OK.  THE LATEST SPC
MESOANALYSIS INDICATES MUCAPE VALUES IN THIS REGION ARE 3000-4000
J/KG, ON THE HIGH END FOR THE WET MULTICELL ENVIRONMENT.  SOME CIN
LIES ALONG THE SYSTEM'S WARM FRONT.  A LOW- TO MID-LEVEL CAP
COVERS MUCH OF NE AND KS, AS IMPLIED BY THE 12C ISOTHERM AT 700
HPA.  PRECIPITABLE WATER VALUES IN THIS REGION ARE CLOSE TO 1.50"
PER 00Z RAOBS AND GPS PRECIPITABLE WATER VALUES. 

PRECIPITABLE WATER VALUES ARE EXPECTED TO RISE TO THE 1.5-1.75"
RANGE PER RECENT RAP FORECASTS, WHICH WOULD BE NEAR THE 75TH
PERCENTILE FOR AUGUST 20.  INCREASING 850 HPA INFLOW -- TO THE
35-40 KT RANGE PER RECENT RAP FORECASTS -- ELEVATES OVER A WARM
FRONT WITHIN A MODERATELY BROAD ZONE INTO A RELATIVELY UNCAPPED
REGION OF EASTERN NE, EASTERN KS, SOUTHWEST IA, AND NORTHWEST MO
AND IS EXPECTED TO LEAD TO THE FORMATION OF A NORTHWEST-SOUTHEAST
THUNDERSTORM BAND ACROSS THIS REGION PER COORDINATION WITH SPC. 
THIS INFLOW EXCEEDS THE MEAN 850-400 HPA WINDS IN THE REGION BY
10-15 KTS, IMPLYING GOOD PRECIPITATION EFFICIENCY.  THE INCREASING
INFLOW NEAR CLOUD BASES COULD ALSO CAUSE THE INITIAL STORMS TO
BACKBUILD.  FORWARD PROPAGATING CORFIDI VECTORS SUGGEST SOUTH OF
DUE EAST MOVEMENT AT ~20 KTS, THOUGH ADDITION OF THE MEAN WIND
AND/OR THE INFLUENCE OF EXPECTED COLD POOL FORMATION SHOULD LEAD
TO CELL MOTION MORE TOWARD THE SOUTHEAST AT 40+ KTS, SIMILAR TO
THAT SEEN THE PREVIOUS COUPLE NIGHTS ACROSS THIS AREA.  THE
EXPECTED ORIENTATION OF THE THUNDERSTORM BAND IS EXPECTED TO BE
ROUGHLY PARALLEL TO THE FORWARD PROPAGATION, MAKING CELL TRAINING
A POTENTIAL PROBLEM FOR A FEW HOURS AFTER THUNDERSTORM FORMATION. 
AVAILABLE MOISTURE IMPLIES HOURLY RAIN RATES UP TO 2", WITH LOCAL
AMOUNTS CLOSER TO 4" POSSIBLE.  MOST THE MESOSCALE GUIDANCE DOES
NOT ALLOW THIS CONVECTION TO FORM UNTIL AFTER 09Z, IF AT ALL,
THOUGH MOST GUIDANCE HAS MISPLAYED THE ONGOING CONVECTION ACROSS
SOUTHWEST SD AND NE -- THERE IS CONSIDERABLE UNCERTAINTY IN THIS
FORECAST.  FLASH FLOODING IS CONSIDERED POSSIBLE.

ROTH

ATTN...WFO...SGF...DMX...EAX...OAX...TOP...ICT...GID...

ATTN...RFC...ABRFC...MBRFC...

LAT...LON   40289335 39539275 38779279 38149362 37639475 37709579
            38159612 38439621 39619668 40389717 41329796 41899739
            41999617 41289464 40439354 40289335