MESOSCALE PRECIPITATION DISCUSSION 0687
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
349 AM EST TUE DEC 22 2015
 
AREAS AFFECTED...SOUTHEAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 220752Z - 221452Z
 
SUMMARY...FLASH FLOODING IS POSSIBLE ACROSS PARTS OF
ALABAMA...GEORGIA...AND SOUTH CAROLINA THROUGH 15Z.

DISCUSSION...A STATIONARY FRONT EXTENDING FROM MONTGOMERY TO ABOUT
MACON...AUGUSTA
AND CHARLOTTE CONTINUES TO STRENGTHEN IN RESPONSE TO THE
APPROACHING UPPER TROUGH INCLUDING WARM ADVECTION SOUTH OF THE
FRONT AND DIABATIC COOLING NORTH OF IT. THE RESULT IS A STRONGER
FRONT WITH COMPENSATING FRONTOLYTIC RESPONSE. ADDITIONALLY...A
WELL DEFINED SURFACE LOW OVER SOUTHEAST ALABAMA CONTINUES TO MOVE
ALONG THE FRONT ENHANCING ASCENT. 

OBSERVED AND RADAR DERIVED RAIN RATES WITHIN CLOSE PROXIMITY OF
THE LOW HAVE PEAKED AROUND 1.5 IN/HR WITH A DURATION OF ABOUT 2
HOURS.

RECENT RUNS OF THE HRRR AND OTHER HI-RES GUIDANCE CAPTURE THE
ONGOING SYNOPTIC AND MESOSCALE ENVIRONMENTS REASONABLY WELL...AND
ALLOW THE LOW TO CONTINUE MOVING NORTHEASTWARD THROUGH GEORGIA AND
PARTS OF SOUTH CAROLINA THROUGH 18Z...SUPPORTING A NARROW CORRIDOR
OF VERY HEAVY RAINFALL ALONG AND JUST NORTH OF THE FRONTAL
BOUNDARY...AND ALONG AND JUST SOUTH OF INTERSTATE 85.

ALTHOUGH INSTABILITY FOR VERTICAL DEVELOPMENT IS NEAR ZERO...THE
SLOPING FRONTAL BOUNDARY MAY SUPPORT SOME SLANTWISE CONVECTION
ENHANCING THE ALREADY HIGH RAINFALL RATES. MODELS ALSO SHOW THE
CLOUD LAYER WINDS WEAKENING SLIGHTLY AND LOW LEVEL JET INCREASING
AND VEERING THROUGH 15Z...WHICH WOULD HELP TO CREATE SLOWER CELL
MOTIONS AND INCREASE THE LIKELIHOOD OF SOME BACK BUILDING OR
LONGER DURATIONS RAINS.  FFG VALUES ACROSS NORTHERN GEORGIA AND
UPSTATE SOUTH CAROLINA ARE 2.5 TO 3 INCHES IN 3 HOURS...WHICH HAS
A CHANCE OF BEING EXCEEDED. IF NOT FLASH FLOODING...THE TIMING OF
THE HEAVY RAIN DURING RUSH HOUR AND HOLIDAY TRAVEL MAY BE
PROBLEMATIC BY ITSELF.  

JAMES

ATTN...WFO...BMX...CAE...FFC...GSP...

ATTN...RFC...SERFC...

LAT...LON   35058201 35058122 34208178 33548248 32748349 
            32058477 32358534 33178494 33928408 34608300