MESOSCALE PRECIPITATION DISCUSSION 0021
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EDT THU APR 02 2015
 
AREAS AFFECTED...SOUTHEAST MO AND THE LOWER OH RIVER VALLEY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 021744Z - 022344Z
 
SUMMARY...A THIN BAND OF THUNDERSTORMS HAS RECENTLY DEVELOPED
ACROSS SOUTH-EASTERNMOST MO AND WESTERNMOST KY.  THIS BAND SHOULD
LENGTHEN EAST-NORTHEASTWARD WITH TIME, WHICH COULD LEAD TO CELL
TRAINING.  WITH HOURLY RATES UP TO 1.5", FLASH FLOODING IS
POSSIBLE.

DISCUSSION...A SHORTWAVE MOVING ACROSS WESTERN IA AND NORTHWEST MO
COMBINED WITH AN OUTFLOW BOUNDARY AT THE SURFACE HAS CAUSED THE
RECENT DEVELOPMENT OF A THIN THUNDERSTORM BAND ACROSS SOUTHEAST MO
AND WESTERNMOST KY.  THE MESOSCALE GUIDANCE HAS MISSED THE
DEVELOPMENT OF THIS BAND, WHICH IS GENERALLY ALIGNED ALONG THE
AXIS OF THE MEAN FLOW.  PRECIPITABLE WATER VALUES OF 1.25-1.5" LIE
IN THIS REGION, WITH MIXED LAYER CAPE VALUES OF 1000-2000 J/KG
ACROSS THE REGION PER THE SPC MESOANALYSIS PAGE.  INFLOW AT 850
HPA IS CLOSE TO 50 KTS PER REGIONAL VAD WIND PROFILES, EXCEEDING
THE MEAN 850-400 HPA WIND, AND CAUSING ~35 KNOTS OF LOW-LEVEL WIND
SHEAR BETWEEN THE SURFACE AND 850 HPA.  THE WIND FLOW IS NEARLY
UNIDIRECTIONAL WITH HEIGHT, WHICH SHOULD PERSIST INTO THE EVENING
HOURS.  BULK SHEAR WITHIN THE LOWER 6 KM IS ALSO CLOSE TO 50
KNOTS, SUPPORTING THE DEVELOPMENT OF ORGANIZED
THUNDERSTORMS/SUPERCELLS ALONG WITH WET MULTICELLS.  WET BULB ZERO
HEIGHTS ARE APPROACHING 10,000 FEET, IMPLYING WARM RAIN PROCESSES
ARE POSSIBLE.

THE AVAILABLE MOISTURE SUPPORTS HOURLY RAIN RATES UP TO 1.5".  THE
OUTFLOW BOUNDARIES ACROSS THE REGION COULD PUSH SLIGHTLY FARTHER
SOUTHEAST BEFORE STALLING OVER THE NEXT FEW HOURS.  THE 12Z RUNS
OF THE ARW, SPC WRF, NMMB, WRF4NSSL, NAM CONEST SHOW A SIGNAL FOR
2-4" OF RAIN BETWEEN NOW AND 00Z, THOUGH 50-100 MILES FARTHER TO
THE NORTH.  RECENT RAP RUNS APPEAR BETTER PLACED TO THE SOUTH PER
RECENT RADAR IMAGERY.  IT IS LIKELY THAT THE CURRENT THUNDERSTORM
BAND AND RELATED OUTFLOW BOUNDARIES COULD INTERCEPT INFLOW FROM
AREAS CLOSER TO THE COLD FRONT.  THE EXPECTATION IS FOR THIS BAND
TO ELONGATE TO THE EAST-NORTHEAST AND POTENTIALLY TRAIN PER
850-400 MEAN WINDS AND FORWARD PROPAGATING CORFIDI/PROPAGATION
VECTORS.  THE PRESENCE OF SUPERCELLS COULD LEAD TO SOME LINE
SEGMENTATION AND/OR WAVES WITH TIME.  FORECAST CAPE AND
PRECIPITABLE WATER FIELDS INDICATE ISSUES COULD EXTEND AS FAR
EAST-NORTHEAST AS THE IN/OH/KY BORDER DURING THIS PERIOD.  FLASH
FLOODING IS CONSIDERED POSSIBLE.

ROTH

ATTN...WFO...ILN...ILX...IND...LMK...LSX...MEG...PAH...SGF...

ATTN...RFC...LMRFC...NCRFC...OHRFC...

LAT...LON   39318483 38808395 37528557 36568854 36259004 
            36289084 36509121 37089126 37599016 38308884 
            38878691