MESOSCALE PRECIPITATION DISCUSSION 0257
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1039 AM EDT SUN JUN 21 2015
 
AREAS AFFECTED...NORTHEAST TX...SOUTHERN OK 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 211430Z - 211930Z
 
SUMMARY...VERY SLOW-MOVING SHOWERS AND THUNDERSTORMS TO CONTINUE
THROUGH MID AFTERNOON WITH FLASH FLOODING LIKELY.

DISCUSSION...THE LATEST SATELLITE IMAGERY SHOWS A WELL-DEFINED AND
VERY SLOW MOVING VORT ACROSS NORTHEAST TX WHICH IS EMBEDDED WITHIN
A DEEPLY MOIST ENVIRONMENT. A CLUSTER OF COLD-TOPPED SHOWERS AND
THUNDERSTORMS ASSOCIATED WITH THE VORT HAS ALREADY PRODUCED NEARLY
5 INCHES OF RAIN AS PER DUAL-POL ESTIMATES ACROSS SOUTHEAST COLLIN
COUNTY...WITH CONVECTION OVER THE LAST HOUR OR SO SEEN EXPANDING A
BIT IN COVERAGE. IN FACT...CONVECTION HAS BEEN GRADUALLY
DEVELOPING TO THE NORTH ACROSS THE RED RIVER INTO PARTS OF FAR
SOUTHERN OK.

PWATS ARE NEAR 2 INCHES ACROSS THE REGION...AND WITH VERY WEAK
STEERING FLOW WITHIN THE DEEPER CLOUD LAYER...LOCALLY VERY HEAVY
RAINFALL TOTALS ARE EXPECTED TO MATERIALIZE. THE LATEST HRRR
SUGGESTS CONVECTION CONTINUING THROUGH MID AFTERNOON AS LOW LEVEL
SURFACE MOISTURE CONVERGENCE COMBINES WITH SOME UPTICK IN
DIURNALLY DRIVEN INSTABILITY. DEEPER LAYER FORCING ASSOCIATED WITH
THE VORT SHOULD PERSIST AS WELL.

IN FACT...THE LATEST HRRR SUGGESTS AREAS ALONG AND NEAR THE RED
RIVER SEEING STORM TOTAL RAINFALL AMOUNTS APPROACHING 10 INCHES
WHICH TENDS TO BE BELIEVABLE GIVEN THE SLOW STORM MOTION AND VERY
HIGH RAINFALL RATES WHICH ARE FORECAST TO BE OVER 2 INCHES/HR.
GIVEN ALL OF THIS FLASH FLOODING IS LIKELY...AND RUNOFF PROBLEMS
WILL BE EXACERBATED LOCALLY FOR AREAS ALREADY IMPACTED THIS
MORNING BY HEAVY RAIN.

ORRISON

ATTN...WFO...FWD...OUN...SHV...TSA...

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

LAT...LON   34949574 34619483 33869448 33219483 32949569 
            32899664 33079735 33479788 34029791 34669721