MESOSCALE PRECIPITATION DISCUSSION 0290
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
944 AM EST SAT DEC 21 2013
 
AREAS AFFECTED...ERN AR...WRN TN AND MS...NE TX...NRN LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 211443Z - 211943Z
 
SUMMARY...EXPECTING INCREASING RAINFALL EFFICIENCY AS DEEP LAYER
ASCENT ARRIVES DURING FAVORABLE DIURNAL HEATING CYCLE. TRAINING
CELLS MAY QUICKLY PRODUCE 2-3 INCHES OF RAIN WITH LOCAL TOTALS
APPROACHING 4 INCHES.

DISCUSSION...AN ONGOING MCS WAS ALIGNED WITH THE LARGELY
UNIDIRECTIONAL FLOW IN PLACE ABOVE 850 MB. THE ASSOCIATED COLD
POOL WAS DRIVING THE LEADING EDGE STEADILY EASTWARD...BUT MAINLY
OVER NORTHEAST ARKANSAS WHERE LOW LEVEL FLOW WAS SOMEWHAT VEERED
IN THE WAKE OF A SUBTLE SHORTWAVE. EASTWARD PROGRESS WAS SLOWER
OVER SOUTHERN ARKANSAS...WHERE CELLS WERE ALSO MORE VIGOROUS OWING
TO GREATER CAPE. 

WITH THE UPPER LEVEL WAVE EJECTING TOWARD THIS REGION...THE HIGH
RESOLUTION MODELS ARE UNANIMOUS IN PRODUCING A SWATH OF HEAVY RAIN
IN THE 15-21Z TIME FRAME...BUT THEY DO SO FARTHER NORTH AND WEST
IN ARKANSAS AND MISSOURI. LOW LEVEL FLOW WILL STRENGTHEN...WHICH
DOES CAUSE PREDICTED INDIVIDUAL CELL MOTION AND MCS MOTION TO BACK
BETWEEN 15-18Z...BUT THE PRE-EXISTING COLD POOL WILL LIKELY
POSITION THE AXIS OF HEAVIEST CONVECTIVE RAINS FARTHER SOUTH AND
EAST. ADJUSTING THE 11Z HRRR OUTPUT FOR THIS...WOULD EXPECT THE
HEAVY RAIN THREAT TO CONCENTRATE ACROSS THE OUTLINED AREA. THIS
INCLUDES SOME PORTIONS OF THE POST-FRONTAL ENVIRONMENT IN NE
TX...WHERE THE FRONTAL INVERSION WAS VERY SHALLOW AND THE COVERAGE
OF DEEP CONVECTION WAS SEEN INCREASING AT 1430Z.

PRECIPITABLE WATER VALUES WHERE INCREASING RAPIDLY UP TOWARD 1.70
INCHES PER SOUNDINGS AND SATELLITE DATA. RAIN EFFICIENCY SHOULD
INCREASE...WITH RATES APPROACHING 1.5 INCHES PER HOUR. CELL
MOTION...EVEN FOR RIGHT MOVERS...WILL REMAIN ROUGHLY PARALLEL TO
CORFIDI VECTORS THROUGHOUT THE DAY...SUGGESTING TRAINING CELLS
WITH THE POTENTIAL TO DELIVER FLOODING RAINS.

BURKE

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

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

LAT...LON   31429384 31729268 32209150 33309029 34608941 35588897
            36118918 36288971 36189038 35619147 34729242 33859369
            33499460 32609510 31749487 31429384