Graphic for MPD #0776
MESOSCALE PRECIPITATION DISCUSSION 0776
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
754 PM EDT THU AUG 31 2017

AREAS AFFECTED...NORTHERN MS...WESTERN & CENTRAL TN...NORTHERN
AL...EXT SOUTHERN KY

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

VALID 010000Z - 010600Z

SUMMARY...STRONG MOISTURE FLUX/ASCENT THROUGH THE
TROWAL/DEFORMATION ZONE GENERALLY PARALLEL TO THE TRACK OF HARVEY
POSES LIKELY FLASH FLOODING RISK THROUGH EARLY OVERNIGHT HOURS.

DISCUSSION...WSR-88D MOSAIC DEPICTS HARVEY AS TAKING ON A MORE
CLASSIC EXTRATROPICAL CYCLONE APPEARANCE WITH WELL DEFINED COMMA
HEAD ACROSS NW MS...EFFECTIVE COLD FRONT/INNER CURVED SOLID SQUALL
LINE ACROSS NW AL.  A STRONG SOUTHERLY AND SOUTHEASTERLY FLOW
(35-40KTS AT 85H IN ADVANCE IN THE WARM SECTOR ACROSS CENTRAL
AL/GA ASCENDING OVER THE WARM FRONT INTO CENTRAL/EASTERN TN IN AN
IMPRESSIVE TROWAL SCATTERED WITH EMBEDDED CONVECTIVE ELEMENTS.

EVENTUALLY THE TROWAL MELDS INTO THE LARGER DEFORMATION ZONE FROM
N MS TO S CENTRAL KY THAT IS REINFORCED TO THE NORTH AND IS
ORIENTED FAIRLY PARALLEL TO THE EXPECTED TRACK OF
HARVEY...ALLOWING FOR PROLONGED MODERATE TO HVY RAINFALL WITH
RATES OF 1-1.5" TO PERSIST FOR HOURS LEADING TO 4-7" TOTALS ACROSS
W AND CENTRAL TN BLEEDING INTO S CENTRAL KY AND E CENTRAL TN
TOWARD 06Z.  HI-RES CAM SOLUTIONS CONTINUE TO SHOW STRONG
AGREEMENT THOUGH RAPID REFRESH GUIDANCE SUCH AS THE HRRR AND ESRL
HRRRV3 INDICATE A SLIGHT EASTWARD TREND WHICH IS BEING CONFIRMED
BY RECENT CONVECTIVE TRENDS PLACING NASHVILLE METRO AREA WITHIN
THREAT OF MAIN HEAVY RAINFALL AXIS.

SOUTHEAST OF THE CONFLUENCE OF THE TROWAL AND DEFORMATION ZONE IN
WEST CENTRAL TN...SOUTH AND SOUTHEASTERLY FLOW ISENTROPICALLY
ASCENDS OVER THE EFFECTIVE WARM FRONT FROM JUST SOUTH OF 1M4 TO
GAD...WITH MEAN CELL MOTIONS TOWARD THE NORTH SUPPORTING THE
POTENTIAL FOR BANDED TRAINING ENVIRONMENTS ACROSS N AL AND SOUTH
CENTRAL TN.  ASCENDED WARM SECTOR ENVIRONMENT SUPPORTS INCREASED
INSTABILITY (1000-1500 MUCAPE) ALLOWING FOR STRONGER/BROADER
UPDRAFTS CAPABLE OF 2"/HR RATES.  DEPENDENT ON DURATION OF
TRAINING...TOTALS UP TO 3-5" ARE POSSIBLE POSING FLASH FLOODING
RISK ACROSS THIS REGION AS WELL THROUGH 06Z ESPECIALLY CLOSER TO
THE INTERSECTION WITH THE DEFORMATION ZONE.   

GALLINA

ATTN...WFO...BMX...HUN...JAN...LMK...MEG...OHX...PAH...

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

LAT...LON   37278522 36798516 36388521 35248593 34668585
            33908579 33938770 34768817 34748871 33698962
            33669074 34559093 35709019 36408913 36928784
            37158647


Last Updated: 754 PM EDT THU AUG 31 2017