MESOSCALE PRECIPITATION DISCUSSION 0660
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
817 AM EDT WED AUG 09 2017

AREAS AFFECTED...N-CNTRL TO ERN GA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 091216Z - 091615Z

SUMMARY...SLOW MOVING CONVECTION WITH TEMPORARY TRAINING
ATTRIBUTES WILL ALLOW A LOCALIZED FLASH FLOOD THREAT TO LINGER
ACROSS PORTIONS OF GA THROUGH 16Z. RAINFALL RATES OF 1-2 IN/HR
WILL BE POSSIBLE.

DISCUSSION...12Z KFFC RADAR DATA SHOWED A NEARLY STATIONARY LOW
LEVEL...SMALL SCALE CIRCULATION AND LOCALLY HEAVY RAINFALL PRESENT
OVER THE NRN ATLANTA METRO REGION...LOCATED ALONG AN 850 MB
BOUNDARY WHICH EXTENDED WEST TO EAST ACROSS GA AT 12Z. LOCAL
WUNDERGROUND.COM OBSERVATIONS HAVE GENERALLY SHOWN THE HIGHEST
RAINFALL RATES TO BE IN THE 1-2 IN/HR ACROSS NRN FULTON...DEKALB
AND SRN GWINNETT COUNTIES WHERE RAINFALL HAS NOT MOVED OVER THE
PAST 3 HOURS. A BIG LIMITING FACTOR IN HEAVIER RAINFALL RATES HAS
BEEN LOW-END INSTABILITY ACROSS THE REGION WITH RAP/HRRR AND THE
SPC MESOANALYSIS PAGE SHOWING ABOUT 500 J/KG OF NEAR SURFACE-BASED
INSTABILITY OVER ATLANTA. FARTHER TO THE SOUTHEAST WHERE
INSTABILITY IS ESTIMATED TO BE CLOSER TO 1000 J/KG...NEARLY
UNIDIRECTIONAL FLOW FROM THE WEST AT ABOUT 15 KT HAS ALLOWED FOR
RADAR ESTIMATED RAIN RATES NEAR 2 IN/HR OVER HANCOCK AND BALDWIN
COUNTIES.

THE LOW LEVEL CIRCULATION OVER THE ATLANTA METRO REGION IS
REPRESENTED REASONABLY WELL IN THE HRRR MODEL OUTPUT AND IS
FORECAST TO DROP SOUTHEAST AND SHEAR OUT OVER THE NEXT 2-4 HOURS.
LOCALLY STRONGER WLY FLOW TO THE SOUTH OF THIS CIRCULATION MAY
ALLOW ADDITIONAL LOCALIZED TRAINING ELEMENTS TO LINGER OVER
PORTIONS OF N-CNTRL TO ERN GA THROUGH 16Z. THE ADDITION OF SOLAR
HEATING AND BOUNDARY LAYER MIXING SHOULD CONTINUE TO WEAKEN
ONGOING ACTIVITY SPECIFICALLY OVER THE ATLANTA METRO REGION WITH
ANY LINGERING THREAT OF FLASH FLOODING LIKELY DIMINISHED IN THE
SHORT TERM. FARTHER TO THE SOUTHEAST HOWEVER...THE FLASH FLOOD
THREAT LOOKS TO LINGER ANOTHER FEW HOURS.

OTTO

ATTN...WFO...CAE...CHS...FFC...

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

LAT...LON   34178394 33588276 33478187 32998154 32428247
            32768384 33538458 34128452