MESOSCALE PRECIPITATION DISCUSSION 0839
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
809 AM EDT THU SEP 28 2017

AREAS AFFECTED...SOUTH-CENTRAL AND SOUTH TEXAS

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

VALID 281208Z - 281708Z

SUMMARY...RAIN WILL CONTINUE TO FALL OVER MUCH OF SOUTH-CENTRAL
AND SOUTH TEXAS...WHICH HAVE RECEIVED SEVERAL CONSECUTIVE DAYS OF
RAIN. LOCALIZED HEAVY RAIN BANDS IN THIS ENVIRONMENT MAY PRODUCE
RAIN RATES UP TO 2 IN/HR AND FLASH FLOODING.

DISCUSSION...LATEST REGIONAL RADAR LOOPS SHOWED A BROAD AND
RELATIVELY DISORGANIZED AREA OF RAIN ACROSS MUCH OF SOUTHERN
TEXAS. THE RAIN WAS SITUATED IN A PLUME OF TROPICAL MOISTURE THAT
HAS BEEN WELL ESTABLISHED FOR SEVERAL DAYS NOW...WITH PRECIPITABLE
WATER VALUES OVER 2 INCHES AND THE CIRA LAYER PW PRODUCT SHOWING
THE MOISTURE PLUME EXTENDING UP THROUGH THE DEPTH OF THE
TROPOSPHERE. SUCH AN ENVIRONMENT WOULD GENERALLY BE ABLE TO
SUPPORT HEAVY RAIN...ALTHOUGH REDUCED INSTABILITY HAS BEEN
LIMITING THE VIGOR AND ORGANIZATION OF RAIN BANDS. THE GREATEST
INSTABILITY SHOULD CONTINUE TO BE FOCUSED IN THE SOUTHERN PORTIONS
OF THE OUTLINED DISCUSSION AREA...AND NEW CONVECTION LATER IN THE
MORNING COULD BE FOCUSED IN THOSE AREAS.

THERE APPEAR TO BE SEVERAL LOW-MID LEVEL MESOSCALE CIRCULATIONS OR
MCVS IN FAR NORTHERN MEXICO TIED TO AREAS OF CONVECTION THAT
LASTED THROUGH MUCH OF THE NIGHT. THESE CIRCULATIONS MAY BE
SLIGHTLY MODIFYING THE WIND FIELD NEARBY AND FOCUSING SEVERAL
AREAS OF LOW-LEVEL CONVERGENCE ACROSS SOUTH TEXAS...SEEN IN
SURFACE OBSERVATIONS AND HINTED AT IN RAP ANALYSIS FROM THE
SURFACE THROUGH 850MB. AS OF 12Z...THIS WAS BEING MANIFEST THROUGH
SEVERAL SLOW-MOVING RAIN BANDS: (1) NEAR DEL RIO TX TO NEAR UVALDE
TX... (2) NORTHERN DUVAL COUNTY TX TO OSO BAY. ALTHOUGH RAIN AND
CONVECTION DID NOT APPEAR VERY ORGANIZED THIS MORNING...THE VERY
MOIST AND TROPICAL ENVIRONMENT COMBINED WITH SEVERAL MESOSCALE
CONVERGENCE BOUNDARIES SHOULD BE SUFFICIENT TO MAINTAIN A THREAT
OF LOCALIZED FLASH FLOODING WHERE RAIN BANDS CAN PERSIST FOR A
COUPLE HOURS.

LAMERS

ATTN...WFO...BRO...CRP...EWX...

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

LAT...LON   30060098 29980054 29779997 29479944 29029902
            28589861 28299776 28079713 27749694 27599707
            27359715 27069728 26979760 26989817 27079871
            26809909 26669934 26989955 27229952 27389966
            27539965 27659987 27950010 28150029 28370046
            28640058 28800070 29020078 29190090 29380113
            29490135 29630149 29770157 29990142