MESOSCALE PRECIPITATION DISCUSSION 0130
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
134 AM EDT SUN MAY 06 2018

AREAS AFFECTED...OUTER BANKS AND FAR EASTERN NORTH CAROLINA

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

VALID 060534Z - 061130Z

SUMMARY...HEAVY RAINFALL IS LIKELY OVER FAR EASTERN NORTH CAROLINA
EARLY THIS MORNING...PARTICULARLY OVER THE OUTER BANKS. LOCALIZED
FLASH FLOODING WILL BE POSSIBLE IF HEAVY RAIN RATES CAN BE
SUSTAINED FOR A FEW HOURS. RAINFALL TOTALS SHOULD REACH AND MAY
EXCEED 3-5 INCHES BY 8 AM EDT IN PARTS OF THE OUTER BANKS.

DISCUSSION...THE LATEST CIRA BLENDED TPW PRODUCT SHOWS 2 INCH
PRECIPITABLE WATER VALUES ENCROACHING ON THE COAST OF THE
CAROLINAS AS OF 05Z...AS DOES THE OBJECTIVE RAP ANALYSIS. THIS IS
FURTHER SUPPORTED BY TWO GPS-PW OBSERVATIONS AROUND 1.9 INCHES
(ONE ON THE SC COAST AND ONE IN NC). BASED ON THE SOUNDING
CLIMATOLOGY (1948-2014) FROM THE MOREHEAD CITY NC AREA...2 INCH
PWATS HAVE GENERALLY NOT BEEN OBSERVED PRIOR TO JUNE 1 WITH AN
EXCEPTION IN THE LAST WEEK OF MAY. THEREFORE...THE ATMOSPHERIC
MOISTURE CURRENTLY PUSHING INTO THE EASTERN CAROLINAS IS QUITE
ANOMALOUS AND IS LIKELY NEAR RECORD LEVELS FOR EARLY MAY. BROAD
LOW-LEVEL INFLOW OFFSHORE SHOULD MAINTAIN THE MOISTURE FLUX
THROUGH SUNRISE AND SUPPORT PERSISTENCE OF HEAVY RAIN.

WHETHER THUNDERSTORMS WILL BE EMBEDDED IN THIS AREA OF HEAVY RAIN
IS ANOTHER QUESTION. OBJECTIVE RAP ANALYSIS SHOWS AROUND 500 J/KG
OF MUCAPE BUT HARDLY ANY LIGHTNING STRIKES HAVE BEEN OBSERVED IN
THE LAST HOUR. THIS MAY BE DUE TO THE NARROW CAPE PROFILE...WITH
DEEP SATURATION ON MODEL FORECAST SOUNDINGS BUT LIMITED CAPE ABOVE
THE -10C LAYER. INDEED MRMS SHOWS LIMITED ICE IN RAIN BANDS (VIA
VERTICALLY INTEGRATED ICE PRODUCT) AND 30 DBZ ECHO TOPS GENERALLY
BELOW THE -10C LAYER. WHILE THIS MAY LIMIT THUNDERSTORMS...IT IS
ALSO HIGHLY TYPICAL OF ENVIRONMENTS WITH DOMINANT WARM RAIN
(COLLISION-COALESCENCE) PROCESSES AND EFFICIENT RAINFALL
PRODUCTION. EVEN IN THE HEAVIER RAIN BANDS...KLTX RADAR SHOWS ZDR
VALUES AROUND OR LESS THAN 1 DB...CONSISTENT WITH SMALLER AND MORE
SPHERICAL RAIN DROPS AND WARM RAIN PROCESSES. RADAR RAINFALL
ESTIMATES MAY STRUGGLE IN THIS ENVIRONMENT...PARTICULARLY AT
LONGER RANGES FROM THE RADAR SITE GIVEN THAT THE BULK OF HIGHER
REFLECTIVITY SHOULD BE CONCENTRATED BELOW 10 KFT.

GIVEN THE MESOSCALE ENVIRONMENT...CONFIDENCE IS HIGH IN HEAVY
RAINFALL. THE 00Z HREF SHOWS A GREATER THAN 70 PERCENT CHANCE OF
5+ INCHES OF RAINFALL OVER THE OUTER BANKS BY 12Z AS A BOUNDARY
LAYER CONVERGENCE MAXIMUM PIVOTS IN AND SHOULD HELP FOCUS HEAVIER
PRECIPITATION. ADDITIONALLY...ALMOST ALL HI-RES MODELS SHOW RAIN
RATES APPROACHING 2 IN/HR IN THE HEAVIEST RAIN BANDS. THIS MAY
TRANSLATE INTO SOME LOCALIZED FLASH FLOODING IF THE HEAVIER RAIN
RATES CAN BE SUSTAINED FOR A FEW HOURS. HOWEVER...THE ANTECEDENT
CONDITIONS AND SANDY SOILS IN THE REGION DO NOT GENERALLY FAVOR
FLASH FLOODING. NEVERTHELESS FLASH FLOODING WILL BE
POSSIBLE...PARTICULARLY IF A HEAVY RAIN BAND CAN BECOME SITUATED
SLIGHTLY FURTHER W/NW OVER MORE URBANIZED INLAND LOCATIONS OF FAR
ERN NC.

LAMERS

ATTN...WFO...AKQ...ILM...MHX...

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

LAT...LON   36297545 35617510 35107530 34707593 34337672
            33807772 33627832 34137856 34937792 35617700
            36127614