MESOSCALE PRECIPITATION DISCUSSION 0767
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
950 AM EDT WED AUG 30 2017

AREAS AFFECTED...EXTREME SE MS...SRN AL...WRN FL PANHANDLE

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

VALID 301345Z - 301845Z

SUMMARY...TRAINING CONVECTIVE CELLS EMBEDDED IN A CHANNEL OF
HIGHER ATMOSPHERIC MOISTURE CONTENT WILL POSE A THREAT FOR FLASH
FLOODING. RAIN RATES OF 2-3 IN/HR WILL BE POSSIBLE WITH STRONGER
CONVECTION.

DISCUSSION...AS OF 13 UTC...REGIONAL RADARS REVEALED A NARROW
RIBBON OF MORE VIGOROUS CONVECTION EXTENDING FROM THE WESTERN TIP
OF THE FLORIDA PANHANDLE SSW INTO THE CENTRAL GULF OF MEXICO. THE
BLENDED-TPW PRODUCT REVEALS THIS IS EMBEDDED IN A PLUME OF HIGHER
PRECIPITABLE WATER VALUES ON THE ORDER OF 2.5 INCHES...AND GPS PW
OBSERVATIONS NEAR MOBILE BAY ARE AS HIGH AS 2.7 INCHES.
THEREFORE...THIS CONVECTION WOULD BE EXPECTED TO BE VERY EFFICIENT
AT RAINFALL PRODUCTION...AND THAT IS CONFIRMED BY OBSERVED DUAL
POL RAIN RATES ON KMOB RADAR AS HIGH AS 2-3 IN/HR.

THE EASTWARD EXTENT OF THE THREAT MAY INITIALLY BE RESTRICTED BY
SOME DRIER AIR TO THE EAST...AS INDICATED IN THE NON-OPERATIONAL
GOES-16 AIR MASS RGB IMAGERY. MEANWHILE...THE WEST AND NORTHWEST
EXTENT MAY BE RESTRICTED BY LOWER INSTABILITY...WITH STRATIFORM
RAIN MORE COMMON OVER THE MS-AL BORDER REGION AND INTO CENTRAL AL.
THEREFORE...THE GREATEST RISK OF FLASH FLOODING THROUGH 18Z IS
EXPECTED TO BE IN THE MIDDLE...ROUGHLY FROM BALDWIN COUNTY ALABAMA
EAST TO OKALOOSA COUNTY FLORIDA.

CONVECTIVE BANDS WITH HEAVY RAINFALL SHOULD PERSIST THROUGH MIDDAY
WITH SEVERAL FACTORS FAVORING MAINTENANCE OF CONVECTION. THERE IS
SOME LARGE SCALE SUPPORT FROM A 50-60 KNOT 300MB JET STREAK THAT
THE RAP HAS EXTENDING FROM CENTRAL MS INTO THE SOUTHERN
APPALACHIANS. THE 12Z BMX SOUNDING HAD A 52 KNOT WIND AT 300MB.
THIS WILL FAVOR UPPER LEVEL DIVERGENCE IN THE RIGHT ENTRANCE
REGION OF THE JET STREAK...OVER THE MPD AREA. STRONG LOW-LEVEL
MOISTURE TRANSPORT WILL ALSO CONTINUE INTO THE AREA. AND CLEAR
SKIES TO THE EAST OF ONGOING CONVECTION SHOULD LEAD TO GREATER
INSTABILITY BY LATE MORNING...WHICH MAY LEAD TO SLIGHTLY EASTWARD
PREFERENTIAL STORM MOTIONS AND A CONTINUED FOCUSING OF THE THREAT
IN THE EASTERN HALF OF THE MPD AREA. FURTHERMORE...INCREASING
TEMPERATURE AND INSTABILITY GRADIENTS WITH DIURNAL HEATING COULD
HELP FOCUS LOW-LEVEL CONVERGENCE...AND CONVECTIVE ELEMENTS THAT
HAVE THUS FAR BEEN MORE SCATTERED MAY BE ABLE TO ORGANIZE INTO
MORE PERSISTENT RAIN BANDS.

RAIN RATES OF UP TO 2-3 IN/HR CAN BE EXPECTED...EVEN IF CONVECTION
REMAINS MORE SCATTERED...WHICH SUPPORTS A RISK OF FLASH FLOODING.
SLIGHTLY HIGHER RATES MAY OCCUR IF CONVECTION CAN ORGANIZE INTO
ONE OR MORE LARGER RAIN BANDS.

LAMERS

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

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

LAT...LON   32388671 32388620 31938592 31518589 30928596
            30358614 30308667 30238728 30178772 30148818
            30258838 30518852 30778859 30968857 31418827
            31888782 32298723