MESOSCALE PRECIPITATION DISCUSSION 0125
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
549 AM EDT TUE APR 18 2017

AREAS AFFECTED...SOUTHEAST TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 180948Z - 181515Z

SUMMARY...POCKETS OF VERY SLOW-MOVING SHOWERS AND THUNDERSTORMS
WITH INTENSE RAINFALL WILL CONTINUE THIS MORNING. ADDITIONAL FLASH
FLOODING IS LIKELY.

DISCUSSION...CYCLONIC FLOW ASSOCIATED WITH A SLOW-MOVING MCV WILL
CONTINUE TO FOCUS POCKETS OF SHOWERS AND THUNDERSTORMS THIS
MORNING ALONG THE MIDDLE AND UPPER TX COAST...AND SOMEWHAT INLAND
CLOSER TO THE VORT CENTER ITSELF. ALREADY ISOLATED AREAS IN
BRAZORIA COUNTY TO THE SOUTHWEST OF HOUSTON HAVE RECEIVED OVER 9
INCHES OF RAIN THIS MORNING DUE TO A CLUSTER OF NEARLY STATIONARY
THUNDERSTORMS. THE CONVECTION IS BEING FACILITATED BY THE VORT
DYNAMICS AND PROXIMITY OF A RATHER STRONG INSTABILITY GRADIENT
ALONG THE COAST. LOW LEVEL SOUTHEAST FLOW IS ALSO TRANSPORTING
DEEPER MOISTURE INTO A SURFACE TROUGH NEAR THE COAST. IN
FACT...PWATS REMAIN RATHER HIGH AND IN THE 1.6 TO 1.8 INCH RANGE
AS PER THE LATEST GPS-DERIVED PWAT DATA.

THIS HIGHER PWAT ENVIRONMENT WILL CONTINUE TO FOSTER RAINFALL
RATES OF AS MUCH AS 2 TO 3 INCHES/HR...AND WITH VERY WEAK STEERING
FLOW OVER THE REGION...THE CELL MOTION WILL BE QUITE SLOW WHICH
WILL HELP ALLOW FOR SOME VERY HEAVY RAINFALL TOTALS. THE LATEST
RUNS OF THE HRRR SUGGEST POCKETS OF AN ADDITIONAL 3 TO 6 INCHES OF
RAIN THROUGH MID-MORNING...AND THIS IS EXPECTED TO FALL ON SOME
AREAS THAT ALREADY RECEIVED VERY HEAVY RAIN. FLASH FLOODING IS
LIKELY.

ORRISON

ATTN...WFO...BRO...CRP...EWX...FWD...HGX...LCH...SHV...

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

LAT...LON   31499522 31329468 30619414 29919410 29429445
            29309464 28969511 28729544 28439603 28169648
            27679698 26999730 27029777 27289797 27829791
            28239762 28619730 29159696 29579696 30359698
            31069681 31459611