MESOSCALE PRECIPITATION DISCUSSION 0381
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
857 PM EDT WED SEP 17 2014
 
AREAS AFFECTED......WEST CENTRAL TX/FAR SOUTHEAST NM... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180056Z - 180556Z
 
SUMMARY...DEVELOPING CONVECTION MERGING OVER PORTIONS OF WEST
CENTRAL TX COULD UPSCALE AS THE LOW LEVEL FLOW BACKS...INTRODUCING
HIGH MOISTURE CONTENT AIR INTO THE REGION. THE RESULTANT HEAVY
RAIN COULD RESULT IN FLASH FLOODING.

DISCUSSION...KLLB RADAR IS SHOWING OUTFLOW DRIVEN CONVECTION ABOUT
TO MERGER WITH EXISTING CONVECTION TO ITS SOUTHEAST. THE MERGER
COULD RESULT IN LOCALIZED FLASH FLOODING...AS ONE HOUR RADAR
ESTIMATES TOP 2 INCHES. 

THE LOW LEVEL FLOW BACKS THROUGH THE EVENING HOURS...AS THE 850 MB
INCREASES TO BETWEEN 20 AND 25 KNOTS. THE LOW LEVEL INFLOW WILL
PUMP UP PRECIPITABLE WATER VALUES TO BETWEEN 1.75 AND 2.00 INCHES.
SYNOPTIC SCALE ASCENT IN ASSOCIATION WITH A SHORT WAVE EMERGING
FROM NM COULD AID IN UPSCALE DEVELOPMENT IN THE CONVECTION...AS IT
TRANSITIONS OUT OF OUTFLOW DRIVEN MODE.

THE LATEST ARW AND CONEST SHOW THE POTENTIAL FOR LOCAL 2-4 INCH
RAINFALL AMOUNTS WITH THE CONVECTION AS IT SPREADS OUT ALONG A LOW
LEVEL BOUNDARY. THE 12Z NAM CONEST SHOWED AMOUNTS AS HIGH AS 7.50
INCHES...BUT GIVEN THE MOTION OF THE CELLS NOW THAT VALUE MAY BE
TOO HIGH. CURRENT THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE AS
LOW AS 1.50 TO 2.00 INCHES ACROSS PORTIONS OF WEST CENTRAL TX.

THE HIGH RESOLUTION GUIDANCE SUGGESTS THAT THE IN SITU INSTABILITY
WANES THROUGH THE EVENING...AND MAY END UP BEING THE LIMITING
FACTOR FOR ADDITIONAL DEVELOPMENT AFTER 06Z. BEFORE THEN...FLASH
FLOODING IS CONSIDERED POSSIBLE.

HAYES

 

ATTN...WFO...LUB...MAF...SJT...

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

LAT...LON   33420123 33280035 32899975 32450010 32170146 
            32060240 32020310 32100333 32590338 32680338 
            33040284 33330174 33370163