MESOSCALE PRECIPITATION DISCUSSION 0174
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 PM EDT SAT MAY 19 2018

AREAS AFFECTED...WEST-CENTRAL TO NORTHERN TX...SOUTHWEST TO
SOUTH-CENTRAL OK

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

VALID 200355Z - 200900Z

SUMMARY...VERY HEAVY RAINFALL FROM SLOW-MOVING SHOWERS AND
THUNDERSTORMS WILL CONTINUE TO POSE A FLASH FLOOD THREAT OVER THE
NEXT SEVERAL HOURS.

DISCUSSION...A RELATIVELY BROKEN AXIS OF HEAVY SHOWERS AND
THUNDERSTORMS WITH VERY COLD CONVECTIVE CLOUD TOPS IS SEEN
PERSISTING ACROSS PORTIONS OF WESTERN AND NORTHERN TX AND INTO
SOUTHWEST OK. THIS INCLUDES A NUMBER OF SLOW-MOVING SUPERCELLS.

THE CONVECTION HAS BEEN FOCUSING ALONG A QUASI-STATIONARY FRONT
WHERE MODERATE INSTABILITY REMAINS POOLED ALONG IT. IN ADDITION TO
THE INSTABILITY...THE MOISTURE PROFILES ARE QUITE CONDUCIVE FOR
HEAVY RAINFALL GIVEN AN AXIS OF 1.2 TO 1.4 INCH PWATS WHICH IS
ABOUT 1.5 TO 2 STANDARD DEVIATIONS ABOVE NORMAL. ALL OF THIS IS
BEING FACILITATED BY A 30 TO 40 KT LOW LEVEL JET WHICH IS LIFTING
NORTH UP ACROSS MOST OF CENTRAL AND WESTERN TX AND OVER THE
AFOREMENTIONED FRONT. THE ACTIVITY ALSO IS BEING FAVORED BY SOME
MODEST RIGHT-ENTRANCE REGION JET DYNAMICS DOWNWIND OF AN UPPER
TROUGH AXIS THAT IS BEGINNING TO EJECT OUT ACROSS THE SOUTHERN
HIGH PLAINS.

A RATHER WIDESPREAD AXIS OF CONVECTION WILL CONTINUE OVER THE NEXT
SEVERAL HOURS ALONG THE FRONT WITH A TENDENCY OVERNIGHT FOR
CONVECTION TO GRADUALLY SETTLE MORE TO THE SOUTHEAST AS THE FRONT
BEGINS MOVING SOUTHEAST AS A COLD FRONT...AND ALSO WITH THE AID OF
SOME REGIONAL CONVECTIVE COLD POOL GENERATION. THE CELLS THOUGH
WILL STILL BE SLOW-MOVING...AND THERE WILL BE A CONCERN FOR
MULTIPLE CELL-MERGERS WHICH WILL ENHANCE THE RAINFALL RATES.

EXPECT THE RAIN RATES TO BE AS MUCH AS 2.5 INCHES/HR...AND SOME
STORM TOTALS BY 09Z MAY REACH AS MUCH AS 6 INCHES GIVEN THE SLOW
MOVEMENT. FLASH FLOODING IS LIKELY AS A RESULT.

ORRISON

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

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

LAT...LON   35209723 34489668 33739715 33049887 32830032
            32880161 33040239 33410276 33840258 34110182
            34370015 34719905 35129835