MESOSCALE PRECIPITATION DISCUSSION 0881
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 PM EDT MON OCT 09 2017

AREAS AFFECTED...SOUTHERN MS & SOUTHWEST AL

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

VALID 092004Z - 100204Z

SUMMARY...THUNDERSTORMS ARE SHOWING INCREASING COVERAGE ACROSS AN
AREA THAT HAS RECEIVED 3"+ OF RAIN LATELY.  HOURLY TOTALS TO 3"
WITH LOCAL AMOUNTS TO 5" ARE POSSIBLE.

DISCUSSION...WATER VAPOR IMAGERY SHOWS A SHORTWAVE LIFTING
NORTHEAST NEAR THE LA/TX BORDER WHICH ALONG WITH AN UPPER HIGH TO
THE EAST IS SPONSORING DIVERGENCE ALOFT OVER THE AREA.  INFLOW AT
850 HPA IS CONVERGENT AT ~20 KTS PER VAD WIND PROFILES, WHICH IS
SLIGHTLY MORE THAN THE MAGNITUDE OF THE MEAN 850-400 HPA WIND. 
THUNDERSTORMS ARE FORMING NEAR A MESOSCALE WAVE ACROSS MS.  ML
CAPE VALUES OF 1500+ J/KG LIE IN ITS WARM SECTOR.  EFFECTIVE BULK
SHEAR OF ~25 KTS COMBINED WITH THE RELATIVELY UNIDIRECTIONAL FLOW
OUT OF THE SOUTH-SOUTHWEST HAS BEEN ATTEMPTING TO ORGANIZE
OCCASIONAL LINEAR CONVECTIVE BANDS ACROSS THE REGION OVER THE PAST
SEVERAL HOURS.  PRECIPITABLE WATER VALUES ARE ~2.4" PER GPS DATA.

THE 12Z SSEO NEIGHBORHOOD PROBABILITIES SHOW CONVECTION IN THE
VICINITY MAY HOLD ON UNTIL 02Z, SO USED A SIX HOUR WINDOW.  RECENT
HRRR/HRRR PARALLEL RUNS SHOW LOCAL AMOUNTS ~5" OVER THE NEXT
SEVERAL HOURS, WHICH IS POSSIBLE CONSIDERING THE PARAMETERS
PRESENT.  EXPECT THUNDERSTORMS TO SPREAD BACK INTO SOUTHWEST AL
WITH TIME PER FORWARD PROPAGATING CONVECTIVE VECTORS.  THERE
SHOULD BE SOME DECREASE IN ORGANIZATION PAST 00Z AS WINDS AT 850
HPA RELAX.  UNTIL ORGANIZATION LESSENS, HOURLY RAIN TOTALS UP TO
3" WITH LOCAL AMOUNTS TO 5" ARE POSSIBLE.

ROTH

ATTN...WFO...BMX...JAN...LIX...MOB...

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

LAT...LON   32148807 32098713 31208699 30368747 30188795
            30188846 30178908 30368941 30728948 31398901