MESOSCALE PRECIPITATION DISCUSSION 0123
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 PM EDT MON APR 17 2017

AREAS AFFECTED...SE AR, NORTHERN MS, WESTERN & CENTRAL TN

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 171910Z - 172310Z

SUMMARY...CONVECTION WITH HEAVY RAIN IS MOVING ALONG A STALLING
OUTFLOW BOUNDARY AND A WEAK FRONTAL WAVE.  HOURLY RAIN RATES TO
2", WITH LOCAL AMOUNTS OF 2-4", COULD LEAD TO FLASH FLOODING.

DISCUSSION...EXPERIMENTAL GOES-R SATELLITE IMAGERY SHOWS AN ARRAY
OF CIRCULATIONS NEAR AR AND WESTERN TN, INCLUDING A PAIR OF MCVS. 
AT THE SURFACE, THE MAIN BOUNDARY IS ONE STRETCHING FROM SOUTHEAST
AR ACROSS NORTHWEST MS INTO WESTERN TN, WHICH THEN EXTENDS EAST
FROM A FRONTAL WAVE ACROSS SOUTH-CENTRAL TN.  HEAVY RAINFALL HAS
BEEN MOST FOCUSED ALONG THE TRAILING BOUNDARY ACROSS NORTHWEST MS.
 A SECOND OUTFLOW BOUNDARY IS ENTERING SOUTHWEST AR AND APPEARS TO
BE HOLDING UP THE MOVEMENT OF THE EASTERN BOUNDARY.  PRECIPITABLE
WATER VALUES NEAR 1.5" EXIST IN THIS AREA.  BULK SHEAR IN THE 0-6
KM LAYER IS 25-30 KTS, WHICH COULD LEAD TO SOME CONVECTIVE
ORGANIZATION. MLCAPES OF 1000-1500 J/KG EXIST ACROSS THE REGION.

THE GFS-BASED GALVEZ-DAVISON INSTABILITY INDEX IMPLIES INCREASING
CONVECTIVE COVERAGE EAST OF THE WAVE ACROSS WESTERN AND CENTRAL TN
WHICH HAS BEEN APPARENT IN RECENT SATELLITE AND RADAR IMAGERY. 
THERE IS TIME FOR ANOTHER 500 J/KG OF MLCAPE/MUCAPE TO BUILD
AREAWIDE PRIOR TO SUNSET.  A SLIGHT AMOUNT OF INCREASE IN THE
LOW-LEVEL INFLOW IS EXPECTED OVER THE NEXT FEW HOURS ACROSS TN. 
WITH MINIMAL MOVEMENT TO THE TRAILING BOUNDARY, HEAVY RAIN
CONCERNS ALSO EXIST FROM SOUTHEAST AR ACROSS NORTHWEST AND
NORTHERN MS IN ITS VICINITY OVER THE NEXT SEVERAL HOURS.  SLOW
CELL MOTION TO THE EAST IS MAIN ISSUE ACROSS AR/MS WHILE CELL
TRAINING APPEARS TO BE THE ISSUE ACROSS TN, WHERE STORMS SHOULD
MOVE EAST TO EAST-SOUTHEAST AT 20-25 KTS.  HOURLY RAIN RATES UP TO
2", WITH LOCAL AMOUNTS OF 2-4", COULD BROADEN THE FLASH FLOOD
CONCERNS ACROSS THIS AREA. 

ROTH

ATTN...WFO...BMX...FFC...HUN...JAN...LZK...MEG...MRX...OHX...
SHV...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   36248563 35598400 34828573 33858963 33069159
            33019234 34829019 36198847