MESOSCALE PRECIPITATION DISCUSSION 0136
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 PM EDT WED JUN 18 2014
 
AREAS AFFECTED...PORTIONS OF THE DAKOTAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 181944Z - 190014Z
 
SUMMARY...CONVECTION WITH EXPANDING AND COOLING TOPS, ALONG WITH
RAIN RATES EXCEEDING AN INCH AN HOUR, ARE DEVELOPING OVER AREAS
WITH SATURATED SOILS.  A FEW OCCURRENCES OF FLASH FLOODING ARE
ANTICIPATED THROUGH 00Z.

CONVECTION IS FIRING NORTH OF THE 700 HPA 12C ISOTHERM NEAR AND
ALONG A TROWAL EXTENDING NORTHWEST FROM A SURFACE LOW IN SOUTHERN
SD.  THE TROWAL ITSELF SHOWS DECENT LOW-TO MID-LEVEL
FRONTOGENESIS, WHICH IS LIKELY LEADING TO THE CONVECTIVE UPSWING. 
THE WARM 700 HPA TEMPS ARE A REFLECTION OF THE MID-LEVEL CAP, AND
SHOULD KEEP CONVECTION ELEVATED NORTH OF THE EFFECTIVE FRONTAL
ZONE LYING ACROSS SOUTHEAST SD AND WESTERN IA.  CAPES OF 2000-4000
J/KG EXIST IN THE REGION, AND 0-3 KM SHEAR IS ROUGHLY 30 KTS. 
COMBINED WITH PRECIPITABLE WATER VALUES OF 1.50-1.75 INCHES --
NEAR THE 95TH PERCENTILE OF MID-JUNE -- AND THE STAGE IS SET FOR
THE WET MULTI-CELL ENVIRONMENT.  SOUNDINGS IN THE REGION SHOW WET
BULB ZERO HEIGHTS IN THE 10,000-11,000 FOOT RANGE ABOVE GROUND
LEVEL, WHICH COULD ALLOW WARM RAIN PROCESSES TO CONTRIBUTE TO
RAINFALL EFFICIENCY.  CORFIDI VECTORS ARE NEAR 10 KTS ALONG THE
TROWAL, WHICH SHOULD LEAD TO MINIMAL CELL MOTION.

THERE IS A MODERATE SIGNAL IN THE MESOSCALE QPF GUIDANCE SHOWING
LOCAL MAXIMA OF 2-3" OVER THE NEXT SEVERAL HOURS, WITH THE MOST
RECENT RUNS OF THE ARW, HRRR, WRF NSSL, NAM CONEST, AND 12Z SSEO
MEAN HAVING THE BEST HANDLE OF THE ONGOING CONVECTION.  AVAILABLE
MOISTURE IN THE REGION SUPPORTS HOURLY RAINFALL RATES OF 2" AN
HOUR IN STRONGER STORMS, WHICH WOULD EASILY EXCEED THE LOW FLASH
FLOOD GUIDANCE VALUES.  HOWEVER, AREAL COVERAGE OF THE CONVECTION
MAY NOT BE ALL THAT LARGE, WHICH LED TO THE DECISION FOR POSSIBLE
FLASH FLOODING OVER LIKELY.  USED 00Z AS THE VALID TIME TO WATCH
HOW CONVECTION TRIES TO DEVELOP INTO AREAS FARTHER EAST, WHICH
SHOULD SEE AN UPSWING IN THEIR 850 HPA INFLOW BEYOND 00Z.  A FEW
LOCALES COULD EXPERIENCE FLASH FLOODING THROUGH 00Z.

ROTH

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LAT...LON   45019762 44360022 44490149 45540306 46920395 47960403
            48260245 47000019 45239734 45019762