MESOSCALE PRECIPITATION DISCUSSION 0904
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
113 PM EDT SUN OCT 22 2017

AREAS AFFECTED...SERN MS/SRN AL/WRN FL PANHANDLE

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

VALID 221712Z - 222045Z

SUMMARY...A LOCALIZED FLASH FLOOD THREAT WILL CONTINUE ACROSS
PORTIONS OF THE CNTRL GULF COAST OVER THE NEXT FEW HOURS. RAINFALL
RATES OF NEAR 3 IN/HR ARE EXPECTED TO ALLOW FOR 3-5 INCH RAINFALL
TOTALS OVER A 2 HOUR PERIOD THROUGH 20Z.

DISCUSSION...RADAR IMAGERY THROUGH 1645Z CONTINUED TO SHOW A SLOW
MOVING CLUSTER OF HEAVY RAINFALL MOVING THROUGH SERN MS INTO SWRN
AL. RATES OF 3-4 IN/HR WERE REPORTED IN SRN HARRISON COUNTY MS
ENDING NEAR 15Z...WITH KLIX DUAL POL ESTIMATES SHOWING SIMILAR
RAINFALL RATES EASTWARD INTO JACKSON COUNTY AS OF 1645Z. IT
APPEARS JUST RECENTLY THAT THERE HAS BEEN MORE OF AN EASTWARD PUSH
TO THE AXIS OF HEAVY RAINFALL COMPARED TO 2-3 HOURS
AGO...PREVIOUSLY MOVING BETWEEN 5-10 KT. LOW LEVEL CONFLUENT FLOW
INTO THE CNTRL GULF COAST CONTINUES TO SUPPORT THE HEAVY RAINFALL
CLUSTER BENEATH A DIFFLUENT FLOW PATTERN ALOFT AMID PRECIPITABLE
WATER VALUES OF 1.9 TO 2.1 INCHES. FARTHER UPSTREAM...AN ELONGATED
OUTFLOW BOUNDARY CONTINUES TO LESSEN THE GAP BETWEEN IT AND THE
SLOW MOVING CLUSTER OF HEAVY RAIN ALONG THE MS/AL BORDER.

WHILE LOW CONFLUENT FLOW IS EXPECTED TO CONTINUE...UPPER LEVEL
DIFFLUENCE WILL WEAKEN SLIGHTLY FROM ITS CURRENT STATE THROUGH 20Z
AS FLOW ALOFT BECOMES MORE ALIGNED FROM THE SOUTHWEST AHEAD OF AN
APPROACHING UPPER TROUGH. RECENT HI-RES MODELS HAVE BEEN TOO SLOW
WITH THE ELONGATED UPSTREAM OUTFLOW BOUNDARY...WITH CURRENT
OBSERVATIONS SHOWING THE BOUNDARY MOVING AT ABOUT 30 KT. GIVEN
THIS MOVEMENT AND THE CURRENT MOVEMENT OF THE SLOW MOVING AXIS OF
HEAVY RAIN TO ITS EAST...THE TWO MAY MEET UP IN ANOTHER 3-4
HOURS...OR BETWEEN 20-21Z...WHICH COULD FINALLY DISRUPT THE
ONGOING FLASH FLOOD THREAT. UNTIL THEN HOWEVER...FLASH FLOODING IS
LIKELY TO CONTINUE ON A LOCALIZED BASIS WITHIN ABOUT 70 MILES OF
THE COAST.

OTTO

ATTN...WFO...LIX...MOB...TAE...

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

LAT...LON   31308808 31288715 31178628 30668601 30138619
            29858727 30148880 30958879