MESOSCALE PRECIPITATION DISCUSSION 0829
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 PM EDT TUE SEP 26 2017

AREAS AFFECTED...WRN AND NW TEXAS...FAR SC OKLAHOMA

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

VALID 261847Z - 270030Z

SUMMARY...FLASH FLOOD THREAT WILL CONTINUE FROM WEST AND NORTHWEST
TEXAS INTO SOUTH-CENTRAL OKLAHOMA WITH SLOW MOVING RAIN BANDS AND
THUNDERSTORMS PRODUCING RAIN RATES UP TO 2 IN/HR.

DISCUSSION...A NEARLY CONTINUOUS BAND OF LOW-TOPPED CONVECTION HAS
DEVELOPED ALONG A SURFACE BOUNDARY THAT IS A COMPOSITE OF AN
EXISTING QUASI-STATIONARY FRONT AND CONVECTIVE OUTFLOWS. GOES-16
IR SATELLITE CHANNELS SHOW A LACK OF COLD CLOUD TOPS (GENERALLY
ALL -30C OR WARMER ON BAND 14)...SUGGESTIVE OF LOW-TOPPED
CONVECTION. CROSS SECTIONS FROM AREA RADARS SUGGEST MOST OF THE
HIGH-REFLECTIVITY ECHOES ARE CONCENTRATED BELOW -10C...A LOW-ECHO
CENTROID SIGNATURE INDICATIVE OF DOMINANT WARM RAIN PROCESSES AND
POTENTIALLY MORE EFFICIENT RAINFALL PRODUCTION. GOES-16 DAY CLOUD
PHASE RGB AND BAND 5 (SNOW-ICE CHANNEL) IMAGERY ALSO SHOW ONLY
SCATTERED POCKETS OF ICE CLOUDS.

DUAL POL RAINFALL ESTIMATES FROM SOME OF THE AREA RADARS HAVE
GENERALLY BEEN UNDERESTIMATING RAIN RATES AS COMPARED TO
OBSERVATION SITES. ODESSA (KODO) MEASURED AROUND 1 INCH BETWEEN
1-2 PM LOCAL TIME...WHILE KMAF RADAR DUAL POL ESTIMATES WERE
AROUND HALF THAT AMOUNT. MRMS ESTIMATES HAVE BEEN CLOSER TO
SURFACE OBSERVATIONS IN GENERAL...AND HAVE SHOWN RAIN RATES
PEAKING IN THE 1-2 IN/HR RANGE WHERE CONVECTION HAS BEEN ABLE TO
TRAIN A SUFFICIENT AMOUNT OF TIME. THIS MAY LEAD TO FLASH
FLOODING...PARTICULARLY IN LOCATIONS IN WHICH HEAVIER RATES CAN
PERSIST FOR 2-3 HOURS.

THE LONGER DURATIONS OF HEAVY RAIN SEEM TO BE MOST LIKELY NEAR
ABILENE AND THE TEXAS BIG COUNTRY...OR NEAR THE INTERSECTION OF A
LOW-LEVEL CONVERGENCE AXIS EXTENDING TO THE SOUTHEAST...AND THE
AFOREMENTIONED QUASI-STATIONARY FRONT. KDYX RADAR SHOWS A BAND OF
LOW-TOPPED CONVECTION STREAMING NORTHWEST ALONG THE CONVERGENCE
AXIS INTO THE AREA...AND AN ABUNDANCE OF LOW-TOPPED CONVECTION
ALREADY ALONG THE FRONT. THE COMBINATION OF THESE TWO CONVECTIVE
FOCI SHOULD MAINTAIN HEAVY RAIN IN THE AREA FOR THE NEXT SEVERAL
HOURS AND COULD LEAD TO SOME LOCALLY HIGHER RAINFALL TOTALS AND
SLIGHTLY HIGHER LIKELIHOOD OF FLASH FLOODING. RAP FORECASTS SHOW
HIGHER PRECIPITABLE WATER VALUES ADVECTING NORTHWEST INTO THE
FRONT IN THIS REGION OF TEXAS OVER THE NEXT SIX HOURS...SO IT IS
ALSO CONCEIVABLE THAT RAIN RATES WILL INCREASE THROUGH THE
AFTERNOON.

LAMERS

ATTN...WFO...FWD...LUB...MAF...OUN...SJT...

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

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            33569790 33429819 33169843 32749837 32499828
            32059844 31729861 31529892 31519941 31729983
            31720024 31570072 31270136 31060225 30810282
            31050342 31600353 32150306 32310259 32550195
            32770125 33010068 33560002 33819969 34269889
            34599812 34819729