MESOSCALE PRECIPITATION DISCUSSION 0674
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 PM EDT SAT AUG 12 2017

AREAS AFFECTED...SOUTHERN OK...NORTHERN TX

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

VALID 121945Z - 130100Z

SUMMARY...EXPANDING SLOW MOVING CONVECTION GROWING UPSCALE WITH
POTENTIAL FOR TRAINING IN VICINITY OF RED RIVER.

DISCUSSION...EXPERIMENTAL GOES-16 6.9UM MID-LEVEL WV CHANNEL
DEPICTS MAIN SYNOPTIC SHORTWAVE CURRENTLY APPROACHING THE SW
CORNER OF OK WHILE FURTHER SOUTH A MORE FOCUSED MESOSCALE MCV CAN
BE SEEN WELL IN DYX RADAR LIFTING NORTH AS WELL.  BOTH ARE
PROVIDING EXCELLENT DPVA AND COMBINED WITH PERIPHERAL RIGHT
ENTRANCE DYNAMICS FROM E-W JET ACROSS OK/KS INTO THE OZARKS
PROVIDING EXCELLENT MID TO UPPER LEVEL ASCENT. PERSISTENT CLOUD
COVER NORTH OVER S CENTRAL OK ALONG WITH CLEARING SOUTH OF THE RED
RIVER HAS FURTHER STRENGTHENED FRONTAL ZONE WHILE ALLOWING SFC T
TO REACH THE 90S AND TDS TO REMAIN IN THE LOW 70S.  THIS SUPPORTS
SBCAPES UP TO 4000 J/KG.  AS SUCH GOES-16 VIS SHOWS SIGNIFICANT
CONVECTIVE GROWTH ACROSS N TX FROM SPS TO JDD WITH GREATER
COVERGE/CLUSTERING FURTHER NW TOWARD THE MCV.  SOME MILD MID-LEVEL
DRYING NEEDS TO BE OVERCOME IN THE SHORT-TERM THOUGH CELLS WILL
BECOME INCREASINGLY EFFICIENT WITH TIME...WITH RATES NEAR 2"/HR. 
ADDITIONALLY IN THE SHORT-TERM CELLS ARE CURRENTLY SETTING UP OVER
THE AREA THAT HAS REMAINED MOST DRY OVER THE LAST WEEK OR SO PER
AHPS ANOMALIES AND FFG VALUES...PRESENTING SOME TIME BEFORE FF
CONDITIONS MAY BE REACHED.

GIVEN INFLUENCE OF THE DIFFERENTIAL HEATING...IT APPEARS HI-RES
GUIDANCE IS STRUGGLING A BIT TO HANDLE THE EVOLUTION PARTICULARLY
THE EARLIER ACTIVATION.  HOWEVER...THE 17Z ESRL HRRRV3 APPEARS TO
BE SOLVING THE NEAR TERM THE BEST.  AS THE SHORTWAVE LIFTS NORTH
CELLS WILL CROSS THE RIVER AND POTENTIAL ELEVATE SLIGHTLY GIVEN
THE BOUNDARY...HOWEVER...INCREASED EFFECTIVE BULK SHEAR AND
VEERING STEERING FLOW (TOWARD THE EAST) SET UP THE POTENTIAL FOR
CONVECTION TO TRAIN OVER WETTER SOILS A PRESENT INCREASED RISK OF
FLASH FLOODING THROUGH 00Z...PARTICULARLY ACROSS SOUTH CENTRAL OK.
GIVEN THE 17Z HRRRV3 SUGGESTS RAINFALL TOTALS OVER 3-4" IN THE
NEXT 6HRS FLASH FLOODING IS CONSIDERED LIKELY.

FURTHER EAST ALONG THE LINE CURRENTLY IN NE TX... WITH WEAKER
STEERING FLOW CELLS MAY REMAIN A BIT MORE ISOLATED BUT ALSO HAVE
LIMITED STEERING FLOW/NEAR ZERO PROPAGATION VECTORS.  AS SUCH
THERE WILL BE A GREATER TENDENCY TO HAVE A STRONG
UPDRAFT/DOWNDRAFT COUPLING WITH 2-3" TOTALS BEFORE PROPAGATING ON
THE OUTFLOW TOWARD REMAINING INSTABILITY...THIS WILL EVENTUALLY
PRESENT AN ISSUE NEARER THE RIVER WHERE GROUND CONDITIONS ARE MOST
SATURATED (IN VIC OF LAMAR/FANNIN/RED RIVER/DELTA COUNTIES) WHERE
RAIN TOTALS OVER THE LAST 7 DAYS ARE OVER 600% OF NORMAL...AND AS
SUCH FLASH FLOODING IS HIGHLY PROBABLE WITH CELLS THAT FORM HERE
AS WELL.

GALLINA

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

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

LAT...LON   34709776 34609602 33759481 32549458 32939673
            32529790 32469895 33359934 34379865