MESOSCALE PRECIPITATION DISCUSSION 0017
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
906 PM EST THU JAN 21 2016
 
AREAS AFFECTED...PORTIONS OF THE CENTRAL GULF COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 220206Z - 220806Z
 
SUMMARY...THUNDERSTORMS WITH HEAVY RAINFALL COULD CAUSE FLASH
FLOOD ISSUES OVER THE NEXT SEVERAL HOURS, BEFORE THE CONVECTIVE
SYSTEM EVOLVES INTO A NARROWING SQUALL LINE AFTER 06Z.

DISCUSSION...RECENT SATELLITE/RADAR IMAGERY INDICATES
THUNDERSTORMS WITH HEAVY RAIN BETWEEN THE WESTERN FL PANHANDLE AND
SOUTHEAST LA, AHEAD OF A COMPLEX LOW PRESSURE AREA MOVING EASTWARD
THROUGH THE GULF COASTAL PLAIN AHEAD OF A MID-LEVEL CYCLONE
LOCATED NEAR THE ARKLATEX.  SOME OF THE ACTIVITY IS BEING CAUSED
BY A SQUALL-LINE LIKE FEATURE MIGRATING OUT OF LA/SOUTHERN MS
WHILE THE REMAINDER OF THE STORMS ARE FORMING WITHIN THE WARM AIR
ADVECTION REGIME NORTH OF A WARM FRONT LOCATED IN THE GULF OF
MEXICO.  PRECIPITABLE WATER VALUES ARE MODEST, IN THE 1-1.25"
RANGE PER RECENT GPS VALUES WHICH IS ABOUT 1.5 SIGMAS ABOVE THE
MEAN FOR LATE JANUARY.  MUCAPES ARE HIGHEST IN THE GULF OF MEXICO,
WITH 1000+ J/KG VALUES ROUGHLY NEAR/SOUTH OF THE 30TH PARALLEL PER
RECENT SPC MESOANALYSES.  THIS INSTABILITY IS BEING LURED
NORTHWARD BY 40-50 KT 850 HPA INFLOW OUT OF THE SOUTH TO SOUTHWEST.

THE CAM GUIDANCE IS ADVERTISING LOCAL AMOUNTS IN THE 2-4" RANGE IN
THIS REGION, WHICH COULD FALL QUICKLY, NEARING THREE HOURLY FLASH
FLOOD GUIDANCE VALUES.  WITH PRECIPITABLE WATER VALUES FORECAST TO
RISE NEAR 1.5", HOURLY RAIN RATES UP TO 1.75" ARE POSSIBLE WHERE
CELL MERGERS/SHORT PERIODS OF CELL TRAINING TAKE PLACE, WHICH HAS
OCCURRED RECENTLY PER DUAL-POL RADAR ESTIMATES.  THESE SORT OF
RAIN RATES WOULD BE MOST TROUBLESOME IN URBAN AREAS SUCH AS AROUND
BILOXI MS, MOBILE AL, AND PENSACOLA FL.  WHILE FORWARD PROPAGATING
CONVECTIVE VECTORS SUGGEST EAST-NORTHEAST MOTION, THE ORIENTATION
OF THE 1000-500 THICKNESS PATTERN IN THE REGION IS WEST-NORTHWEST
TO EAST-SOUTHEAST; HEAVY RAIN CORES ARE EXPECTED TO GENERALLY MOVE
FROM WEST TO EAST AT 40-45 KNOTS.  BETWEEN 06-09Z, THE
PRECIPITATION PATTERN IS EXPECTED TO SIMPLIFY/NARROW INTO A
PROGRESSIVE SQUALL LINE CONFIGURATION PER RECENT CAM GUIDANCE AND
THE 12Z NAM, WHICH SHOULD LESSEN THE FLASH FLOOD THREAT THEREAFTER.

ROTH

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

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

LAT...LON   32658723 32548582 31978541 30838539 30198607 
            30128677 30088859 29648876 29358901 29118896 
            28928923 28909005 28909101 29989043 31328931 
            32378841