MESOSCALE PRECIPITATION DISCUSSION 0388
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1114 AM EDT THU SEP 18 2014
 
AREAS AFFECTED...CENTRAL TX...SE TX...FAR SW LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 181513Z - 182013Z
 
SUMMARY...LARGE SCALE FORCING WILL OVERSPREAD A REGION
CHARACTERIZED BY UNUSUALLY MOIST AND MODERATELY UNSTABLE AIR. WHEN
COMBINED WITH WET SOILS FROM RECENT RAINS...INSTANCES OF FLASH
FLOODING APPEAR LIKELY THIS MORNING AND THIS AFTERNOON.

DISCUSSION...ONGOING CONVECTION HAD BECOME FAIRLY WIDESPREAD IN SE
TX...AND IS LIKELY TO PERSIST AS A NORTHERN STREAM SHORTWAVE
TROUGH BRUSHES ACROSS THIS REGION...ENHANCING DEEP LAYER ASCENT AS
WELL AS SOUTHWESTERLY INFLOW WINDS AT 850 TO 600 MB. HIGH
RESOLUTION MODELS ARE SIMILAR IN PREDICTING NEW CONVECTION UP INTO
THE TX HILL COUNTRY ALONG A SHARPENING MID LEVEL TROUGH AXIS. AN
UNUSUALLY MOIST ENVIRONMENT AND SUFFICIENT INSTABILITY WILL YIELD
VERY HEAVY RAIN. THE GREATEST CONCENTRATION OF RAIN AND
PERSISTENCE IS EXPECTED OVER SE TX AHEAD OF A DEVELOPING 700 MB
CIRCULATION SEEN IN THE RAP BY 20Z. THOUGH STRENGTHENING WIND
FIELDS MAY CARRY THE EVENT EAST TOWARD SW LOUISIANA...THE WESTERN
FLANK OF LINE SEGMENTS OR THE FLANK OF A SMALL MCS WILL MORE
STRONGLY INTERCEPT INFLOW...PLACING THE GREATEST THREAT OF
EXCESSIVE RAINS AND FLASH FLOODING IN THE VICINITY OF HOUSTON AND
EVENTUALLY POINTS TO THE EAST.

OF PARTICULAR CONCERN...BROAD MESOCYCLONES HAVE ALREADY BEEN
OBSERVED OWING TO VEERING WIND PROFILES AND ABOUT 25 KT OF DEEP
LAYER SHEAR. BOTH THE MEAN 0-6 KM WINDS AND BUNKERS MOTION FOR
RIGHT-MOVING CELLS ARE AROUND 10 KT...BUT THOSE CELLS THAT DEVELOP
MESOCYCLONES WILL TEND TO ANCHOR HEAVY RATES...ON A SPORADIC
BASIS. SUCH ACTIVITY WAS ALREADY OBSERVED WHERE FLASH FLOODING WAS
REPORTED JUST NORTHWEST OF HOUSTON AT 1430Z. WHEREVER CELLS BECOME
ANCHORED 4 INCHES OF RAIN COULD OCCUR IN UNDER 2 HOURS.

BURKE

ATTN...WFO...EWX...FWD...HGX...LCH...SHV...SJT...

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

LAT...LON   31499767 31099588 31119397 30419290 29439253 
            28769381 28719515 29529704 30779884 31489890