MESOSCALE PRECIPITATION DISCUSSION 0193
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
150 PM EDT THU MAY 24 2018

AREAS AFFECTED...SOUTHERN SC...CENTRAL GA...CENTRAL AL

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

VALID 241800Z - 250000Z

SUMMARY...INCREASING COVERAGE OF SLOW MOVING CONVECTION ACROSS
PORTIONS OF THE SOUTHEAST IN A HIGH MOISTURE CONTENT AIRMASS MAY
PRODUCE HOURLY RAINFALL RATES NEAR 2.00 INCHES. THESE RAINFALL
RATES COULD RESULT IN A FLASH FLOOD THREAT INTO THE LATE AFTERNOON
HOURS...ESPECIALLY IN AREAS THAT RECEIVED HEAVY RAINFALL IN
PREVIOUS DAYS.

DISCUSSION...REGIONAL RADARS ARE SHOWING AN INCREASE IN CONVECTIVE
COVERAGE ACROSS SC/GA/AL EARLY THIS AFTERNOON. THE CONVECTION IS
FORMING IN THE PRESENCE OF A WEAK MID LEVEL LOW OVER SOUTH CENTRAL
GA... WHERE THE LOW CLOUD COVER IN STARTING TO BREAK. THE BREAKING
CLOUD COVER HAS ALLOWED MLCAPES TO JUMP TO BETWEEN 1000-1500 J/KG,
STRETCHING FROM SOUTHEAST AL ACROSS CENTRAL GA INTO WEST CENTRAL
SC.

THE MOST RECENT RAP ANALYSIS/BLENDED TPW PRODUCT SHOWED AN AXIS OF
1.75 INCH PRECIPITABLE WATER AIR OVER THIS AREA, AND THE DEEP
MOISTURE HAS ALREADY ALLOWED SMALL CELLS TO PRODUCE HOURLY
RAINFALL RATES IN EXCESS OF 1.50 INCHES (BASED ON THE KMXX RADAR)
OVER PORTIONS OF EAST CENTRAL AL/WEST CENTRAL GA. THE MID LEVEL
FLOW REMAINS WEAK ACROSS THE SOUTHEAST STATES, FOSTERING SLOW CELL
MOTIONS, AS WELL THE POSSIBILITY OF SHORT TERM TRAINING AND CELL
MERGERS.  

THE CELL MERGERS AND SHORT TERM TRAINING MAY RESULT IN THE
POTENTIAL OF HOURLY RAINFALL RATES AT OR ABOVE 2.00 INCHES. IN
FACT, THE 12Z HREF MEAN SHOWED HIGH PROBABILITIES OF HOURLY
RAINFALL RATES IN EXCESS OF 2.00 INCHES OVER SOUTH CENTRAL GA
DURING THE 24/21Z THROUGH 25/00Z TIME FRAME. THE MOST RECENT
HRRR/EXPERIMENTAL HRRR...AS WELL AS THE 12Z WRF ARW... INDICATED
LOCAL 3.00/4.00 INCH RAINFALL AMOUNTS...ESPECIALLY WHERE TRAINING
OR CELL MERGERS OCCUR.

WHILE THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE FAIRLY HIGH
OVERALL, CLUSTERS OF STORMS OVER THE PAST FEW DAYS HAVE PRODUCED
HEAVY RAINFALL OVER PORTIONS OF CENTRAL GA INTO FAR EAST CENTRAL
AL. THESE AREAS COULD BE ESPECIALLY VULNERABLE TO FLASH FLOODING,
EVEN IF THE TOTAL CONVECTIVE COVERAGE IS NOT AS GREAT AS PREVIOUS
DAYS. THE THREAT FOR FLASH FLOODING SHOULD BEGIN TO WANE AFTER
25/00Z...AS THE INSTABILITY STARTS TO BECOME EXHAUSTED.

HAYES

ATTN...WFO...BMX...CAE...CHS...FFC...ILM...MOB...TAE...

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

LAT...LON   33747980 32458118 31568516 32088719 33358705