MESOSCALE PRECIPITATION DISCUSSION 0489
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
900 AM EDT FRI JUL 20 2018
AREAS AFFECTED...ERN NC...ERN SC
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 201259Z - 201659Z
SUMMARY...INGREDIENTS FOR SMALL SCALE TROPICAL STYLE RAINFALL WERE
IN PLACE. RAIN RATES MAY BE DECEIVING WITH LITTLE THUNDER...BUT
SLOW MOVEMENT COULD LEAD TO MULTIPLE INCH RAINFALL IN SHORT
DURATION...AND SUBSEQUENT FLASH FLOODING.
DISCUSSION...COASTAL LOW PRESSURE IN THE LOWER TO MIDDLE LAYERS OF
THE ATMOSPHERE WAS EMBEDDED WITHIN A PLUME OF TROPICAL MOISTURE
OVER SOUTH CAROLINA...SPREADING INTO EASTERN NORTH CAROLINA.
SHOWERS...SOME AS DEEP AS 30 KFT...WERE ONGOING AT 1245Z. ALTHOUGH
A FRONTAL BOUNDARY CUT ACROSS THE COAST INTO THE OFFSHORE
WATERS...MOISTURE WAS MORE THAN FAVORABLE FOR HEAVY RAIN NORTH OF
THE BOUNDARY...AND INSTABILITY WAS SUFFICIENT ALONG THE COAST AND
FARTHER INLAND NEAR A 500 MB LOW CENTER LOCATED WEST OF
CHARLESTON.
THE 00Z CHARLESTON SOUNDING AND 12Z MOREHEAD CITY SOUNDING HAD
SAMPLED STEEP ENOUGH LOW LEVEL LAPSE RATES TO CONTRIBUTE TO THE
500-PLUS J/KG MIXED LAYER CAPE VALUES SEEN IN THE SPC MESOANALYSIS
AT 12Z. THUS...AS THE DEEP LAYER LOW DRIFTS NORTHEASTWARD AND
HEIGHT FALLS AS WELL AS DIFLUENT MID TO UPPER FLOW SHOULD CONTINUE
TO YIELD DEEP...SLOW MOVING SHOWERS. WITH ABOUT THE LOWER HALF OF
THE CLOUD BEING ABOVE FREEZING...WARM RAIN PROCESSES WILL
DOMINATE. THE FAIRLY INNOCUOUS LOOKING RADAR ECHOES NEAR
WILMINGTON NC AT 1245Z WERE PRODUCING A DUAL-POL ESTIMATED 1.50
INCHES OF RAIN PER HOUR. AFTER AN INITIAL BURST OF THIS HEAVIER
ACTIVITY...STEADY TROPICAL RAINS NEAR THE 500 MB LOW CENTER MAY
BOOST THE 3 TO 4 HOUR EVENT RAINFALL TOTALS...PRESSING THE FLASH
FLOOD GUIDANCE VALUES...ESPECIALLY IN POORLY DRAINED LOCATIONS.
BURKE
ATTN...WFO...CAE...CHS...ILM...MHX...RAH...
ATTN...RFC...SERFC...
LAT...LON 35547658 35297600 34777594 34437631 33257829
32607989 32718069 33358133 34587937 35187785
Last Updated: 900 AM EDT FRI JUL 20 2018