MESOSCALE PRECIPITATION DISCUSSION 0128
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1048 PM EDT THU APR 20 2017

AREAS AFFECTED...PORTIONS OF OK & NORTHWEST TX

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

VALID 210247Z - 210847Z

SUMMARY...ELEVATED THUNDERSTORMS ARE EXPECTED TO BACKBUILD/TRAIN
NORTH OF A FRONTAL BOUNDARY NEAR THE RED RIVER VALLEY.  HOURLY
RAIN RATES TO 1.75", WITH LOCAL AMOUNTS OF 2-4", COULD LEAD TO
FLASH FLOODING.

DISCUSSION...THE FIRST ISOLATED SHOWERS AND THUNDERSTORMS BEGAN TO
DEVELOP AROUND 02Z NEAR THIS AREA AS LOW-LEVEL INFLOW VEERED TO A
MORE SOUTHERLY DIRECTION ACROSS THE SOUTHERN PLAINS.  AN INCOMING
NEGATIVELY TILTED SHORTWAVE IS INCREASING UPPER DIVERGENCE ALOFT. 
BULK SHEAR IN THE 0-6 KM LAYER IS ~50 KTS PER SPC MESOANALYSES. 
INFLOW AT 850 HPA IS NOW 30-35 KTS OUT OF THE SOUTH, NEAR THE
MAGNITUDE OF THE 850-400 HPA MEAN WIND.  PRECIPITABLE WATER VALUES
OF AROUND 1.25" EXIST IN THIS AREA PER SOUNDINGS AND RECENT GPS
DATA.  PER MID-LEVEL CAPPING ACROSS THE AREA, SEEN ON AREA
SOUNDINGS, INSTABILITY EXISTS UNUSUALLY FAR POLEWARD OF THE
SURFACE BOUNDARY, ON THE ORDER OF 1000-2000 J/KG MUCAPE-WISE.

THUNDERSTORM WILL SHIFT FROM NORTHEASTERLY TO A MORE
EAST-NORTHEAST MOTION AS THEY ATTEMPT TO BACKBUILD, EXPAND, AND
THEN TRAIN ACROSS PORTIONS OF OK WHILE MOVING EAST-NORTHEAST AT
35-40 KTS.  EMBEDDED MESOCYCLONES COULD HELP AMP UP THE HEAVY RAIN
POTENTIAL.  THE MAIN THREAT OF CELL TRAINING IS EXPECTED TO BE
BEYOND 06Z.  WITH TIME, INSTABILITY IS EXPECTED TO ERODE ACROSS
NORTHERN AND CENTRAL OK WHICH SHOULD REORIENT THE CONVECTION TO A
MORE EAST-WEST, AND EVENTUALLY WEST-NORTHWEST/EAST-SOUTHEAST
ORIENTATION.  THE WIND FLOW SHOULD BECOME INCREASINGLY
UNIDIRECTIONAL WITH HEIGHT WITH TIME.  WHILE GUIDANCE APPEARS
UNDERDONE ON AMOUNTS NEAR CHILDRESS, RECENT ARW, HRRR, WRF4NSSL,
AND NAM CONEST GUIDANCE APPEARS TO HAVE A REASONABLE HANDLE ON
THIS CONVECTIVE ACTIVITY.  HOURLY RAIN RATES TO 1.75", WITH LOCAL
AMOUNTS OF 2-4" ADVERTISED BY THE GUIDANCE, COULD CREATE FLASH
FLOOD ISSUES IN HILLY TERRAIN AND URBAN AREAS.

ROTH

ATTN...WFO...AMA...LUB...OUN...TSA...

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

LAT...LON   36679580 36359470 35429499 34409714 34019947
            34300112 35630002 36539770