MESOSCALE PRECIPITATION DISCUSSION 0807
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
319 PM EST MON DEC 26 2016
 
AREAS AFFECTED...ARKANSAS...EXT NORTHEAST TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 262015Z - 270100Z
 
SUMMARY...ISOLATED THREAT OF FLASH FLOODING WITH
BACKBUILIDING/SLOW MOVING CELLS OVER WET GROUND CONDITIONS. 

DISCUSSION...AS MAIN FORCING/UPPER LEVEL DYNAMICS LIFT
NORTHEASTWARD...THE INFLUENCE ACROSS THE SOUTH IS BECOMING FURTHER
REDUCED WITH LESSENING UPPER LEVEL PERIPHERAL RIGHT ENTRANCE
DIVERGENCE MAINLY OVER CENTRAL AR INTO W TN.  STILL BROAD SWLY AND
SOUTHERLY CONFLUENCE IN THE LOW LEVELS OF HIGH MOISTURE AIR WITH
TDS IN THE LOW 70S AND UPPER 60S OBSERVED ACROSS NE TX/N LA INTO
SW AR ATTM AHEAD OF THE FRONT.  EVEN THOUGH SFC AND BOUNDARY LEVEL
WINDS ARE MORE MILD (15 TO 30KTS RESPECTFULLY) BROADER CONFLUENCE
FROM SWLY AND SOUTHERLY STREAMLINES ARE NOTED IN THE VAD NETWORK
AND USING CU STREAMERS ON RADAR AND VISIBLE IMAGERY SUPPORTING
SOLID MASS CONVERGENCE.   PEAK HEATING THROUGH BROKEN SHALLOW CU
HAVE SUPPORTED A STEADY INCREASE OF INSTABILITY WITH SBCAPES
REACHING 2000 J/KG IN SW AR AND HIGHER FURTHER SOUTHWEST INTO N
TX.   THESE COMBINE FACTORS HAVE LED TO INCREASING CONVECTIVE
ACTIVITY BOTH ALONG THE COLD FRONT IN SE OK/SW AR AS WELL AS A
PRE-FRONTAL BOUNDARY FROM NE TX INTO SW AR.  IR TOPS ARE NEARING
-55C WHICH IS NEAR THE EL TEMPS WITH A STEADY INCREASE IN
LIGHTNING SUGGESTING STRONGER VIGOR LIKELY TO SUPPORT RATES OF
1.25-1.5" HR. 

WEAKER FLOW ALOFT BUT STILL FAIRLY STRONG LOW LEVEL INFLOW FROM
THE SW AND S...PROPAGATION VECTORS WILL SUPPORT UPSTREAM
DEVELOPMENT WITH A SLOW SOUTHEASTWARD PROGRESSION AS THE FRONT
SLIPS SOUTH.  THIS MAY SUPPORT EFFECTIVELY STATIONARY OR SLOW
MOVING RAIN CORES WHICH MAY LEAD TO ISOLATED COMPOUNDED TOTALS IN
EXCESS OF 2-2.5" THAT COULD EXCEED FLASH FLOOD GUIDANCE.  THIS IS
PARTICULARLY THE CASE ACROSS AN AXIS FROM JUST WEST OF TEXARKANA
TO MEMPHIS WHERE 300-400% OF NORMAL PER AHPS OVER THE PAST WEEK. 
AS SUCH FFG VALUES MAY HAVE REBOUNDED A BIT QUICKER THAN IN
REALALITY GIVEN WINTER SEASON GROUNDS GOING DORMANT.  GIVEN FFG
ARE IN THE 1.5-2"/1HR AND 2-2.5"/3HR RANGE IT IS WELL WITHIN
POSSIBILITY GIVEN THE RATES AND CELL MOTIONS THIS COULD BE
ECLISPED AND LEAD TO LOCALIZED FLASH FLOODING.  THIS IS BEST
PRESENTED BY THE 12Z WRF-ARW, RECENT RUNS OF THE HRRR, HRRR EXP,
AND RAP.  THIS PROVIDES SOME MODERATE CONFIDENCE IN LOCALIZED
FLASH FLOOD CONDITIONS OCCURRING OVER THE LATE AFTERNOON INTO
EARLY EVENING HOURS ACROSS ARKANSAS..AND NE TEXAS. 

GALLINA

ATTN...WFO...LZK...MEG...SHV...

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

LAT...LON   35769116 35489082 34959067 34579098 33889160 
            33519199 33219364 33299480 34569362 35049245