MESOSCALE PRECIPITATION DISCUSSION 0163
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1017 PM EDT THU MAY 17 2018
AREAS AFFECTED...SOUTHERN APPALACHIANS
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 180215Z - 180815Z
SUMMARY...HEAVY SHOWERS TO PERSIST LOCALLY WELL PAST MIDNIGHT.
ADDITIONAL FLASH FLOODING WILL BE POSSIBLE.
DISCUSSION...VERY MOIST DEEP LAYER SOUTH TO SOUTHEAST FLOW INTO
THE SOUTHERN APPALACHIANS IS EXPECTED TO CONTINUE OVERNIGHT AND
WILL TEND TO MAINTAIN THE THREAT OF HEAVY SHOWERS AS A BROAD UPPER
TROUGH LINGERS OVER THE SOUTHEAST. INSTABILITY PROFILES ARE
GRADUALLY WEAKENING WITH THE LOSS OF DIURNAL HEATING...BUT THE
PRESENCE OF DIFFLUENT FLOW ALOFT AND OROGRAPHIC LIFT OVER THE
HIGHER TERRAIN SHOULD TEND TO COMPENSATE AT LEAST TO THE EXTENT OF
MAINTAIN THE CONVECTIVE SHOWER THREAT OVER THE NEXT SEVERAL HOURS.
IN FACT...THE LATEST HRRR AND HRRR-TLE GUIDANCE ACTUALLY MAINTAINS
THE CONVECTIVE THREAT ACROSS ESPECIALLY WESTERN NC AND EXTENDING
AS FAR SOUTH AS NORTHEAST GA GOING WELL PAST 06Z. ASIDE FROM THE
DEEP LAYER UPSLOPE FLOW...THE SUPPORT FOR THIS IN PART WILL BE
ATTRIBUTED TO MORE FAVORABLE MID LEVEL FORCING/DIVERGENCE ARRIVING
AROUND THE EASTERN FLANK OF THE UPPER LOW OVER THE MID SOUTH.
MOISTURE IS HIGHLY ANOMALOUS ACROSS THE REGION AND RUNNING AS MUCH
AS 2 STANDARD DEVIATIONS ABOVE NORMAL. THE DEPTH OF MOISTURE IS
QUITE DEEP AND THUS WILL PROMOTE HIGHLY EFFICIENT RAIN RATES
PROCESSES THAT WITH THE AID OF OROGRAPHICS WILL PROMOTE RAINFALL
RATES OF AS MUCH AS 2 INCHES/HR.
GIVEN THESE INTENSE RAINFALL RATES OVER ELEVATED TERRAIN AND ALSO
WITH RECENT RAINFALL...THE THREAT OF FLASH FLOODING WILL CONTINUE.
ORRISON
ATTN...WFO...FFC...GSP...MRX...RNK...
ATTN...RFC...LMRFC...OHRFC...SERFC...
LAT...LON 36948091 36638082 36108131 35398201 34508255
34008336 33988420 34298473 34758466 35378413
36088315 36558232 36868150
Last Updated: 1017 PM EDT THU MAY 17 2018