MESOSCALE PRECIPITATION DISCUSSION 0261
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1015 AM EDT FRI SEP 20 2013
 
AREAS AFFECTED...NORTHEAST/CENTRAL TX...SOUTHWEST AR...NORTHWEST
LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 201414Z - 202014Z
 
SUMMARY...HEAVY RAINFALL OVER SATURATED SOILS FROM RECENT RAINS IS
EXPECTED TO CAUSE REGIONAL FLASH FLOODING ACROSS PORTIONS OF
CENTRAL AND NORTHEAST TX AS WELL AS SOUTHWEST AR.

DISCUSSION...THE RAIN EVENT THAT BEGAN YESTERDAY AFTERNOON ACROSS
PORTIONS OF CENTRAL TX CONTINUES FROM THE RIO GRANDE VALLEY INTO
CENTRAL TX, AND FROM EAST OF THE DALLAS/FORT WORTH METROPOLITAN
AREA ACROSS NORTHEAST TX INTO SOUTHWEST AR.  THE FOCUS FOR THE
HEAVY RAINFALL IS A BAROCLINIC TROUGH/FRONTAL ZONE ACROSS THE
CENTRAL RIO GRANDE VALLEY, WITH A SURFACE WAVE NEAR CHILDRESS TX
AIDING THUNDERSTORM ACTIVITY ACROSS NORTHEAST SECTIONS OF THE
STATE. PRECIPITABLE WATER VALUES OF 2.25-2.50 INCHES ACROSS THE
AREA ARE ABOVE THE 95TH PERCENTILE FOR LATE SEPTEMBER FOR THE
REGION, WHICH IS AIDING PRECIPITATION EFFICIENCY.  LOW-LEVEL
INFLOW INTO THE REGION IS ON THE ORDER OF 30 KNOTS INTO NORTHEAST
TEXAS, WITH LESSER VALUES NEAR THE RIO GRANDE.  CAPE VALUES IN THE
SOURCE REGION -- NEAR THE GULF COAST -- ARE IN THE 1000-2000 J/KG
RANGE.  THIS COMBINATION OF INDICES FAVORS ORGANIZED CONVECTION IN
THE FORM OF WET MACROBURST MULTICELLS.  DIVERGENCE ALOFT IS BEING
ENHANCED BY A SOUTHERN STREAM SHORTWAVE MOVING THROUGH THE
SOUTHERN ROCKIES.  

RAINFALL RATES IN THE STRONGER CONVECTIVE CELLS HAVE BEEN
EXCEEDING TWO INCHES PER HOUR, WHICH IS WELL ABOVE THE FLASH FLOOD
GUIDANCE VALUES FOR THE REGION WHICH AVERAGE NEAR 1.5 INCHES IN
THREE HOURS.  CORFIDI VECTORS ARE GENERALLY UNDER 10 KNOTS TO THE
NORTHEAST WITH THIS REGION, WHICH COULD ALLOW FOR SLOW MOVEMENT TO
ORGANIZED CONVECTION.  WITH LOW-LEVEL INFLOW INCREASING ACROSS
EASTERN TX, NORTHWEST LA, AND SOUTHWEST AR, ORGANIZED CONVECTION
SHOULD CONTINUE ACROSS THE REGION THOUGH THE DAY TO TODAY, WITH
THE EMPHASIS SHIFTING INCREASINGLY TOWARDS THE ARKLATEX.  AS A
WHOLE, THE THUNDERSTORM ACTIVITY IS EXPECTED TO SHIFT EASTWARD
THROUGH THE DAY TODAY AS THE SYSTEM SLOWLY PROGRESSES EASTWARD. 
CONSIDERING THE ABOVE, BELIEVE REGIONAL FLASH FLOODING IS LIKELY
HERE.

ROTH

ATTN...WFO...LZK...SHV...TSA...HGX...FWD...OUN...EWX...SJT...
MAF...

ATTN...RFC...ABRFC...LMRFC...WGRFC...

LAT...LON   33449702 34589420 34549187 33059252 31519443 29439832
            28670034 29230102 29450142 29840215 30550181 31750015
            32599864 33449702