MESOSCALE PRECIPITATION DISCUSSION 0024
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
436 AM EST WED JAN 18 2017
 
AREAS AFFECTED...A PORTION OF SOUTHEAST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180935Z - 181500Z
 
SUMMARY...TRAINING CONVECTION COULD RESULT IN A LOCALIZED FLASH
FLOOD THREAT THROUGH MID MORNING.

DISCUSSION...REGIONAL RADARS ACROSS SOUTHEAST TX SHOWED CONVECTION
MOVING NORTH OF A WARM FRONT STRETCHED FROM SOUTH TX INTO
SOUTHWEST LA. A 25 TO 30 KNOT LOW LEVEL SOUTH SOUTHWEST FLOW (AS
SEEN ON REGIONAL VWP) IS TRANSPORTING 500 J/KG OF MUCAPE AND
PRECIPITABLE WATER VALUES NEAR 1.50 INCHES (PER THE LATEST BLENDED
TPW PRODUCT)OVER THE FRONT...FUELING THE LOW TOPPED CONVECTION.
THE IR LOOP SHOWED SLOWLY COOLING TOPS WITH THIS ACTIVITY... WHICH
IS CLOSE TO THE WV DEPICTION OF A WEAK SHORT WAVE IN THE FLOW OVER
SOUTH CENTRAL TX. 

KHGX RADAR SHOWED HOURLY RAINFALL RATES NEAR 1.75 INCHES OVER
NORTHWEST FORT BEND COUNTY AT ABOUT 09Z...SUPPORTED BY A ONE HOUR
RAINFALL OF 1.92 INCHES NEAR KATY.  INCREASING SHEAR HAS ALLOWED
THE CONVECTION TO BECOME SOME MORE DISCRETE (AS SEEN IN THE KHGX
RADAR IMAGERY)...SO IT IS POSSIBLE THAT THE HOURLY RAINFALL RATES
ARE HAIL CONTAMINATED. 

THE LATEST RAP SHOWED THAT THE ELEVATED INSTABILITY CONTINUES TO
SHRINK BACK TOWARD THE COAST THROUGH THE MID MORNING HOURS. THIS
COULD RESULT IN A DOWNWARD TREND IN THE CONVECTION THROUGH 15Z.
BEFORE THAT TIME...THE LATEST HRRR SUGGESTS THAT SCATTERED
2.00-3.00 INCH RAINFALL AMOUNTS ARE POSSIBLE WHERE CONVECTION
TRAINS AND CELL MERGERS OCCUR. THE HRRR SIGNAL FOR HEAVY RAIN
BECOMES LESS DISTINCT TOWARD 15Z... PROBABLY AS THE INSTABILITY
WANES. 

THREE HOUR RAINFALL FLASH FLOOD GUIDANCE VALUES GENERALLY RANGES
BETWEEN 2.50 AND 3.50 INCHES...SO TRAINING AND CELL MERGERS IN THE
HIGH MOISTURE CONTENT AIRMASS WOULD BE NECESSARY FOR FLASH
FLOODING TO OCCUR. 

HAYES

ATTN...WFO...HGX...LCH...SHV...

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

LAT...LON   32359418 32329394 31339381 30719411 30239446 
            29689527 29699562 29939627 30119639 30539630 
            30989584 31369541 31769502 32229451