MESOSCALE PRECIPITATION DISCUSSION 0055
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
351 AM EST THU MAR 01 2018

AREAS AFFECTED...EASTERN TN & NORTHEAST AL

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

VALID 010850Z - 011320Z

SUMMARY...HEAVY RAIN WITH HOURLY TOTALS UP TO 0.5" OVER SATURATED
SOILS RUN THE RISK OF FLASH FLOODING.

DISCUSSION...WIDELY SCATTERED SHOWERS AND THUNDERSTORMS HAVE BEEN
FORMING AS OF LATE IN NORTHWESTERLY FLOW ACROSS NORTHERN AR.  TO
THE EAST, HEAVY RAINFALL HAS BEEN SPREADING EASTWARD ACROSS TN
OVER THE PAST FEW HOURS, WITH MESONET SITES SHOWING OCCASIONAL
RAIN TOTALS OF 0.5" AN HOUR IN WESTERN TN.  THIS IS IN ASSOCIATION
WITH OVERRUNNING RAINFALL OCCURRING NEAR AN AREA OF DECENT 850-650
HPA FRONTOGENESIS NORTH OF A STATIONARY FRONT.  DIVERGENCE ALOFT
IN SATELLITE IMAGERY APPEARS TO BE IMPROVING REGIONALLY TO THE
EAST OF A SIGNIFICANT SHORTWAVE ACROSS WESTERN OK AND THE TX
PANHANDLE.  THE LATEST GPS VALUES SHOW PRECIPITABLE WATER VALUES
1.2-1.6", WHICH IS 2-3 SIGMAS ABOVE AVERAGE FOR EARLY MARCH.  THE
VAD WIND PROFILE FROM NORTHEAST AL SHOWS FAIRLY UNIDIRECTIONAL
FLOW FROM THE WEST-SOUTHWEST FROM 3000 FEET UPWARD, WHICH ALOFT IS
DRAWING PACIFIC MOISTURE FROM OFFSHORE BAJA CALIFORNIA AND IN THE
LOWER LEVELS FROM THE GULF OF MEXICO.

RAINFALL ACROSS AR AND WESTERN TN/NORTHERN MS IS EXPECTED TO FADE
OVER THE NEXT FEW HOURS.  THE CURRENT BATCH OF HEAVY RAIN IN
EASTERN TN CURRENTLY ASSOCIATED WITH THE SURFACE WAVE IN NORTHEAST
AL IS EXPECTED TO BE REPLACED/REINFORCED WITH ENHANCED RAINFALL
FROM THE NEXT WAVE UPSTREAM ACROSS NORTHEAST MS.  FLASH FLOOD
GUIDANCE VALUES FROM 00Z-06Z SHOW AN EXTENSIVE AREA OF ROUGHLY 1"
OR LESS IN THREE HOURS ACROSS AR AND THE MID-SOUTH.  MU CAPE
VALUES ACROSS THE REGION ARE ROUGHLY 100 J/KG, WHICH COMBINED WITH
THE AVAILABLE MOISTURE WOULD ALLOW FOR HOURLY RAIN TOTALS UP TO
0.5".  THIS WOULD BE HEAVY ENOUGH TO EXCEED THE LOW FLASH FLOOD
GUIDANCE VALUES RELATIVELY QUICKLY.  THE MESOSCALE GUIDANCE HAS A
SIGNAL FOR 1-1.5" ACROSS NORTHERN MS, EASTERN TN, AND NORTHERN AL
OVER THE NEXT FIVE HOURS IN THIS AREA.  SINCE THE EVENT IS ONE OF
LONGER DURATION, KEPT THE CATEGORY AS FLASH FLOOD POSSIBLE.

ROTH

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

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

LAT...LON   36338686 36328561 36208497 35918447 35508460
            34938444 34538473 34478599 34438634 34408967
            33859225 35069226 35939036 36198959 36318887
            36058794