MESOSCALE PRECIPITATION DISCUSSION 0175
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1222 PM EDT SUN MAY 20 2018

AREAS AFFECTED...PORTIONS OF CNTRL/E-CNTRL TX

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

VALID 201617Z - 202130Z

SUMMARY...REPEATING ECHOS OF HEAVY RAIN ARE EXPECTED TO PRODUCE A
FLASH FLOOD THREAT FOR PORTIONS OF CENTRAL TO EAST-CENTRAL TEXAS
THROUGH 21Z. 6 HOUR RAINFALL TOTALS OF 3-5 INCHES WILL BE POSSIBLE
IN A FEW LOCATIONS.

DISCUSSION...12Z RAOBS CONFIRMED DEEP LOW LEVEL MOISTURE PRESENT
OVER SOUTH TEXAS WITH 850 MB DEWPOINTS RANGING FROM 14 TO 16C
BETWEEN DALLAS-FORT WORTH AND THE RIO GRANDE. FLOW ALOFT WAS
DIFFLUENT NOTED AT 250 MB WITH SHORT TERM FORECASTS SHOWING A
CONTINUATION OF DIFFLUENCE INTO THE EARLY EVENING. SURFACE
OBSERVATIONS AT 16Z SHOWED A SLOW MOVING OUTFLOW BOUNDARY
EXTENDING NORTHEAST TO SOUTHWEST FROM NEAR GVT TO ACT TO ERV.
CONVECTION WAS ALIGNED JUST WEST OR NORTH OF THE BOUNDARY WITH
CLOUD-BEARING LAYER MEAN WINDS ORIENTED SIMILARLY TO THE OUTFLOW
BOUNDARY AT 10-20 KT. MEANWHILE...LOW LEVEL FLOW WAS ORIENTED MORE
PERPENDICULAR TO THE OUTFLOW BOUNDARY ALLOWING FOR SLOW MOVING AND
REPEATING HEAVY RAINFALL ECHOES. KGRK RAINFALL ESTIMATES WERE
PEAKING NEAR 2 IN/HR AS OF 16Z WHICH MATCHED NEARBY
WUNDERGROUND.COM OBSERVATIONS OF RAINFALL.

VISIBLE IMAGERY SHOWED INVIGORATED CUMULUS SOUTH OF THE OUTFLOW
OVER SOUTH-CENTRAL TEXAS WITH RAP ANALYSIS SOUNDINGS INDICATING
LITTLE TO NO CIN AMID 1500-2500 J/KG CAPE. EXPECT CONTINUED
DEVELOPMENT OF CONVECTION ALONG THE SLOW MOVING OUTFLOW BOUNDARY
WITH REPEATING CELLS CONTAINING EMBEDDED RAINFALL RATES BETWEEN
1.5 AND 2.5 IN/HR. RAINFALL TOTALS OVER THE NEXT 6 HOURS MAY RANGE
IN THE 3-5 INCH RANGE WHICH COULD CAUSE FLASH
FLOODING...ESPECIALLY WITH OVERLAP ACROSS THE MORE SENSITIVE
TERRAIN OF THE TEXAS HILL COUNTRY WEST OF I-35.

OTTO

ATTN...WFO...EWX...FWD...HGX...SJT...

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

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            28809871 28809970 29020034 29740056 30270027
            30529983 31189826 31909737 32299653