MESOSCALE PRECIPITATION DISCUSSION 0835
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
135 PM EDT WED SEP 27 2017

AREAS AFFECTED...SOUTH-CENTRAL AND CENTRAL TEXAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 271732Z - 272200Z

SUMMARY...HEAVY RAIN BANDS ARE LIKELY TO PERSIST TO THE EAST OF A
MID-LEVEL CIRCULATION AND BOTH MAY SHIFT SLOWLY NORTHWEST WITH
TIME THIS AFTERNOON. RAIN RATES UP TO 2-3 IN/HR MAY LEAD TO AREAS
OF FLASH FLOODING.

DISCUSSION...A MESOSCALE CONVECTIVE VORTEX (MCV) CONTINUED TO SHOW
A SLOW DRIFT TO THE NORTHWEST TODAY...WITH A WELL-ESTABLISHED
PLUME OF DEEP TROPICAL MOISTURE IMMEDIATELY TO THE EAST. CIRA
LAYER PW PRODUCTS SHOW THE POCKET OF HIGHER MOISTURE EXTENDS WELL
UP IN TO THE 500-300MB LAYER...AND TOTAL PRECIPITABLE WATER VALUES
LIKELY EXCEED 2 INCHES OVER THE ENTIRE DISCUSSION AREA. THE COLDER
CLOUD TOPS EVIDENT ON IR SATELLITE IMAGERY EARLIER THIS MORNING
HAVE SINCE ERODED...AND MOST OF THE CLOUD TOPS IN THE VICINITY OF
ONGOING HEAVY RAIN BANDS ARE NOW WARMER THAN -30C. THE PERSISTENCE
OF HIGHER LOW-LEVEL REFLECTIVITY ON RADAR COINCIDING WITH THE LOSS
OF MID-UPPER LEVEL CLOUDS IN ICE GROWTH LAYERS MAY PORTEND A SHIFT
TO MORE DOMINANT WARM RAIN PROCESSES AND A SLIGHT UPTICK IN RAIN
RATES.

DURING THE MORNING HOURS...THE HEAVIEST RAINFALL HAS BEEN FOCUSED
OVER PORTIONS OF KINNEY...UVALDE...AND ZAVALA COUNTIES...AND FLOOD
REPORTS FROM THESE AREAS HAVE BEGUN TO TRICKLE IN AS OF 17Z. KDFX
RADAR CONTINUES TO SHOW NEW SHALLOW UPDRAFT GROWTH TO THE SOUTH
AND SOUTHEAST OF ONGOING HEAVY RAIN BANDS...AND THESE RAIN BANDS
ALIGN WITH THE LOW-MID LEVEL MEAN FLOW. ALL THAT SUGGESTS THE
THREAT OF CONTINUED TRAINING OF RAIN BANDS AND THE POSSIBILITY OF
EXACERBATING EXISTING FLOODING. RAIN RATES UP TO 2-3 IN/HR APPEAR
LIKELY IN THE HEAVIER AND MORE PERSISTENT RAIN BANDS.

AS THE MCV...AND THE ASSOCIATED CHANNEL OF LOW-MID LEVEL MOISTURE
TRANSPORT TO ITS EAST...CONTINUE TO DRIFT NORTHWEST THIS AFTERNOON
THE THREAT FOR HEAVY RAIN MAY AS WELL. THUS FAR TODAY...THESE
AREAS IN THE EDWARDS PLATEAU HAVE RECEIVED STEADIER MODERATE
RAIN...BUT THIS MAY PRIME THE AREA FOR FLASH FLOODING LATER IF THE
HIGHER RAIN RATES CAN PUSH INTO THE AREA.

LAMERS

ATTN...WFO...CRP...EWX...MAF...SJT...

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

LAT...LON   31340031 31009970 30659942 30209908 29739868
            29249858 28729869 28249900 28009934 28019986
            28180021 28450052 28830075 29220106 29470128
            29690173 29930192 30410181 30960135 31300091