MESOSCALE PRECIPITATION DISCUSSION 0774
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT THU AUG 31 2017

AREAS AFFECTED...EASTERN AR...NORTHERN MS...SOUTHWEST TN...MO
BOOTHEEL

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 311830Z - 010000Z

SUMMARY...PERSISTENT ASCENT ALONG DEFORMATION ZONE CONTINUE TO
SUPPORT HEAVY RAINFALL LIKELY TO POSE FLASH FLOODING CONDITIONS
THROUGH THIS EVENING. 

DISCUSSION...WSR-88D RADAR MOSAIC AND 6.9UM EXPERIMENTAL GOES-16
WV CHANNEL DEPICTS A BAND/LOBE OF LOW TO MID-LEVEL VORTICITY
PRESSING NORTHWARD ACROSS MS PROVIDING INCREASING DPVA/DYNAMIC
ASCENT ALONG AND IN ADVANCE OF THE W TO E ARCHED BAND FROM E AR TO
NW AL ATTM. ADDITIONAL LARGER SCALE ASCENT IS PRESENT ACROSS
WESTERN TN/NE AR AT THE RIGHT ENTRANCE OF SLIGHTLY DIFFLUENT POLAR
JET DEPICTED WELL BY EXPANDING BAROCLINIC LEAF IN MO.

MODEST INSTABILITY UP TO 1500 J/KG CAPES WITH SKINNY/MOIST
ADIABATIC LAPSE RATE PROFILES ACROSS N MS ALLOWING FOR BROADLY
EXPANDING SHIELD OF PRECIPITATION WITH EMBEDDED CONVECTIVE
ELEMENTS (TORNADIC AT TIMES...SEE SPC WATCH 476 AND MCD 1605 FOR
MORE DETAILS).  THESE CONVECTIVE ELEMENTS GIVEN DEEP MOISTURE
PROFILE WITH TPWS IN EXCESS OF 2.25" SUPPORT WARM CLOUD RAINFALL
PROCESSES WITH CAPABILITY OF 2.5"/HR RATES...THOUGH THE ELEMENTS
ARE PROGRESSIVE THROUGH THE BROADER SHIELD CAPABLE OF 1-1.5"/HR
THESE STREAKS WILL LIKELY POSE THE GREATEST FLASH FLOOD RISK. 

CURRENT TRENDS ARE FOR THIS EXPANDING SHIELD TO RE-ESTABLISH A
BETTER MID-LEVEL DEFORMATION/CONVERGENCE ZONE ACROSS THE MS RIVER
IN E AR/N MS/SW TN OVER THE NEXT 6HRS. HOWEVER....GOES-E 11UM IR
STILL SHOWS COOLING/EXPANDING REGION OVER E AR COINCIDENT WITH
EARLIER DEFORMATION ZONE/BAND EXTENDING NORTH TO THE MO BOOTHEEL
CAPABLE OF 1.0-1.5"/HR FOR THE NEXT 2-3 HRS RAINING OVER AREAS
ALREADY EXPERIENCING LOCALIZED FLOODING CONDITIONS...AND HENCE
PROLONGING THE THREAT HERE AS WELL.  AS SUCH 2-4" TOTALS OVER
DESHA/ARKANSAS/PHILLIPS COUNTIES WHILE 3-6" CAN BE EXPECTED THE
TN/MS BORDER.  THIS EVOLUTION IS CONSIDERED HIGH CONFIDENCE IN
OCCURRING GIVEN STRONG HI-RES GUIDANCE AS WELL AS LARGER SCALE
GUIDANCE SUCH AS THE NAM/GFS/ECMWF/UKMET AGREEMENT ANCHORING SUCH
TOTALS THROUGH 00Z WITH SOME SUGGESTIONS OF 7 OR 8" LOCALIZED
VALUES NOT OUT OF THE REALM OF POSSIBILITY.  AS SUCH FLASH
FLOODING IS CONSIDERED LIKELY.

GALLINA

ATTN...WFO...HUN...JAN...LZK...MEG...

ATTN...RFC...ABRFC...LMRFC...SERFC...

LAT...LON   36439054 35938949 35768831 34858816 33968843
            33998965 33719037 33289104 33189125 33329199
            34329224 35809141