MESOSCALE PRECIPITATION DISCUSSION 0022
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
108 AM EST WED JAN 18 2017
 
AREAS AFFECTED...A PORTION OF SOUTHEAST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180610Z - 181000Z
 
SUMMARY...TRAINING AND CELL MERGERS WITH A CLUSTERS OF STORMS JUST
NORTH OF A STATIONARY FRONT COULD RESULT IN A FLASH FLOOD THREAT
EARLY THIS MORNING.

DISCUSSION...REGIONAL RADARS CONTINUE TO SHOW A CLUSTER OF STORMS
MOVING NORTHEAST JUST NORTH OF A STATIONARY FRONT OVER SOUTHEAST
TX. THE CONVECTION LIES IN AN AXIS OF 500-1000 J/KG OF MUCAPE. A
30 KNOT LOW LEVEL SOUTHERLY INFLOW IS PROVIDING 1.50 INCH
PRECIPITABLE WATER AIR (WHICH IS BETWEEN TWO AND THREE STANDARD
ABOVE THE MEAN) TO NEWLY DEVELOPING CONVECTION. THE MOISTURE
SOURCE HAS ITS ORIGINS IN THE EASTERN PACIFIC...AND THE SOURCE OF
MOISTURE REMAINS DEEP. 

THE KGRK RADAR SHOWED HOURLY RAINFALL RATES AS HIGH AS 2.25 INCHES
NEAR 0535Z ACROSS CALDWELL AND BASTROP COUNTIES...BUT THE HCA
PRODUCT AND RECENT SPOTTER REPORTS INDICATE THAT THESE HOURLY
RADAR-BASED RATES COULD BE HAIL CONTAMINATED. NEWLY DEVELOPING
CONVECTION IS FORMING SOUTH OF THE STATIONARY FRONT...WHERE THE
AVAILABLE INSTABILITY IS HIGHER. AS THE NEWLY DEVELOPING
CONVECTION MERGES WITH THE CURRENT CONVECTION...FLASH FLOODING
BECOMES MORE OF A CONCERN.

THE LATEST HRRR SHOWED LOCAL 2.00-3.00 INCH RAINFALL AMOUNTS JUST
NORTHWEST OF KVCT THROUGH 10Z...WITH LESSER AMOUNTS CENTERED ON A
SURFACE TROUGH EXTENDING NORTHEAST ACROSS INTERIOR SOUTHEAST TX.
THE 00Z NSSL WRF IS NOT AS BULLISH WITH THE SIGNAL EARLY ON...BUT
BY 09Z IT SHOWS A STRIPE OF 3.00 TO 4.00 INCHES OF RAINFALL FROM
K11R TO KUTS. 

THREE HOUR FLASH FLOOD GUIDANCE VALUES IN THIS AREA ARE GENERALLY
BETWEEN 2.50 AND 3.50 INCHES. GIVEN THE DEPTH OF THE RICH MOISTURE
SOURCE...THE THREAT OF CELL TRAINING AND MERGERS...AND THE SIGNAL
FROM THE LATEST HRRR/00Z WRF ARW...FLASH FLOODING IS CONSIDER
POSSIBLE EARLY THIS MORNING. 

HAYES

ATTN...WFO...CRP...EWX...HGX...

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

LAT...LON   30889556 30839520 30219506 29209626 28739709 
            28589759 28939773 29429764 30419649