868
FXUS62 KILM 091820
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
220 PM EDT WED SEP 9 2026
WHAT HAS CHANGED
FORECAST RAIN CHANCES HAVE BEEN INCREASED BY ~20 PERCENT BOTH
SATURDAY AND SUNDAY AFTERNOONS, LARGELY DRIVEN BY NBM. FORECAST
HIGH TEMPS SATURDAY THROUGH TUESDAY HAVE BEEN INCREASED BY 1-2
DEGREES OVER THE PREVIOUS FORECAST. THIS INCREASES FORECAST HEAT
INDICES BY A FEW DEGREES THROUGH THE PERIOD TOO.
KEY MESSAGES
1) SHOWER AND THUNDERSTORM CHANCES WILL INCREASE THIS WEEKEND
AS A FRONT APPROACHES THE AREA.
2) HEAT AND HUMIDITY WILL BUILD AND HEAT INDICES COULD EXCEED
100 DEGREES YET AGAIN.
DISCUSSION
KEY MESSAGE 1...SHOWER AND THUNDERSTORM CHANCES WILL INCREASE
THIS WEEKEND AS A FRONT APPROACHES THE AREA.
A SHALLOW FLOW OF ATLANTIC MOISTURE SHOULD SPREAD ACROSS EASTERN
SOUTH CAROLINA ON THURSDAY. THIS COULD LEAD TO SCATTERED
SHOWERS BREAKING OUT DURING THE DAY. DRY AIR ALOFT WITHIN THE
UPPER RIDGE SHOULD TEND TO LIMIT COVERAGE TO 20-40 PERCENT.
THE PERSISTENT MID AND UPPER LEVEL RIDGE OVER THE CAROLINAS
SHOULD BEGIN TO BREAK DOWN THIS WEEKEND AS A TROUGH DIGS INTO
THE MID MISSISSIPPI VALLEY. THIS SHOULD RESULT IN A DEEPER FLOW
OF GULF MOISTURE AND PRECIPITABLE WATER VALUES SHOULD RISE TO
2.0-2.2 INCHES. AN APPROACHING SYNOPTIC COLD FRONT SHOULD STALL
OUT BEFORE REACHING THIS FAR SOUTH, BUT AN INCREASINGLY
UNCAPPED ATMOSPHERE AND DIFFERENTIAL HEATING/SEABREEZE
BOUNDARIES MAY PROVIDE ENOUGH SUPPORT FOR NUMEROUS SHOWERS AND
STORMS INLAND ON FRIDAY, THEN ACROSS THE ENTIRE AREA SATURDAY
AND SUNDAY. THREE-DAY QPF IS 0.50 TO 1.00 INCH WITH THE OBVIOUS
INCLUSION OF HIGHER AMOUNTS IN HEAVIER STORMS.
IT'S WORTH MENTIONING THE INCREASE IN FORECAST RAIN CHANCES IN
OFFICIAL FORECASTS IS DRIVEN LARGELY BY NBM OUTPUT. MOS
FORECASTS BASED ON THE GFS AND ECMWF REMAIN A GOOD 20-30 PERCENT
LOWER FOR POPS THROUGH THE WEEKEND.
THE VERY HUMID AIRMASS WILL CONTINUE ON INTO EARLY NEXT WEEK,
BUT THE UPPER RIDGE MAY BEGIN TO RESTRENGTHEN ACROSS THE
CAROLINAS. THIS IS SHOWN PARTICULARLY IN THE 12Z GFS AND 00Z
ECMWF, BUT NOT THE 00Z CANADIAN WHICH KEEPS THE RIDGE FARTHER
WEST ACROSS THE LOWER MISSISSIPPI VALLEY. A RIDGE RETURNING
WOULD TEND TO SUPPRESS CONVECTIVE COVERAGE WHICH IS WHAT OUR
FORECAST IS BASED ON FOR NEXT WEEK.
KEY MESSAGE 2...HEAT AND HUMIDITY WILL BUILD AND HEAT INDICES
COULD EXCEED 100 DEGREES YET AGAIN.
DESPITE FALLING SUN ANGLES AND SHORTENING DAY LENGTHS, THE
AIRMASS ACROSS THE CAROLINAS SHOULD RETURN TO UNSEASONABLY HOT
SUMMERTIME LEVELS THIS WEEKEND INTO EARLY NEXT WEEK.
850 MB TEMPS IN THE +18C TO +19C RANGE WOULD BE SLIGHTLY ABOVE
NORMAL IN MID JULY, BUT NOW THAT WE'RE APPROACHING MID SEPTEMBER
IT'S ABOVE THE 90TH PERCENTILE AND ONLY ABOUT 1C AWAY FROM
RECORDS AT THE MOREHEAD CITY UPPER AIR SITE. THIS SHOULD
TRANSLATE TO INLAND HIGH TEMPS 89-93 DEGREES, WHICH WHEN
COMBINED WITH DEWPOINTS WELL INTO THE 70S SHOULD YIELD HEAT
INDICES ABOVE 100 DEGREES.
AS OF NOW WE WON'T HAVE ANY RECORD HIGH TEMPERATURES FORECAST,
BUT THIS JUST PILES ONTO THE EXCESSIVE AMOUNT OF HEAT AND
HUMIDITY WE'VE DEALT WITH ACROSS THE CAROLINAS THIS YEAR.
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
VFR CONDITIONS WILL CONTINUE THROUGH THE AFTERNOON BENEATH A
SCATTERED 5000 FOOT CUMULUS CLOUD DECK AND LIGHT SOUTH TO
SOUTHEAST SURFACE WINDS. AS WINDS DIMINISH TONIGHT, THERE IS A
MODERATE CHANCE FOR MVFR FOG TO DEVELOP AT KLBT AND KFLO
AIRPORTS MAINLY AFTER 10Z. BOTH NBM AND GFS HOURLY STATISTICAL
GUIDANCE INDICATES SOME POTENTIAL FOR VERY LOW IFR STRATUS
CEILINGS TO DEVELOP AT KFLO AS WELL. THESE EARLY MORNING
IMPEDIMENTS SHOULD BURN OFF 13-14Z.
WITH RICHER MOISTURE IN PLACE THURSDAY LOOK FOR A MORE
EXPANSIVE AND SLIGHTLY CUMULUS CLOUD DECK TO DEVELOP DURING THE
MID TO LATE MORNING HOURS. SCATTERED CONVECTIVE SHOWERS COULD
BEGIN TO DEVELOP BEFORE 18Z ACROSS SOUTH CAROLINA.
EXTENDED OUTLOOK...ALTHOUGH VFR CONDITIONS WILL PREVAIL, THERE
IS INCREASING POTENTIAL FOR POP-UP SHOWERS AND THUNDERSTORMS
BRINGING BRIEF MVFR/IFR CONDITIONS, ESPECIALLY SATURDAY AND
SUNDAY. THERE IS ALSO A LOW POTENTIAL FOR LATE NIGHT/EARLY
MORNING STRATUS OR GROUND FOG, PARTICULARLY AFFECTING KLBT AND
KFLO SATURDAY AND SUNDAY.
MARINE
TONIGHT THROUGH MONDAY...HIGH PRESSURE JUST OFF THE EAST COAST
SHOULD RETREAT FARTHER EAST OVER THE NEXT COUPLE OF DAYS AS A
COLD FRONT, CURRENTLY EXTENDING FROM PENNSYLVANIA TO SOUTHERN
ILLINOIS, APPROACHES THE AREA. AT THIS TIME THE FRONT IS
EXPECTED TO STALL ACROSS INLAND NORTH CAROLINA FRIDAY INTO
FRIDAY NIGHT, THEN RETURN NORTH ON SATURDAY. THIS SHOULD LEAD TO
PRIMARILY SOUTHWEST WINDS ACROSS THE AREA, INTERRUPTED AT TIMES
BY VARIABLE THUNDERSTORM OUTFLOW WINDS AS STORMS BECOME MORE
NUMEROUS ACROSS THE AREA SATURDAY.
FOR EARLY NEXT WEEK, WHAT'S LEFT OF THE OLD FRONT COULD GET
PUSHED SOUTH INTO THE AREA AS A NEW AREA OF LOW PRESSURE PASSES
EASTWARD ACROSS SOUTHEASTERN CANADA. WHILE THERE WON'T BE AN
AIRMASS CHANGE ASSOCIATED WITH THIS FEATURE, CONVERGING/SHIFTING
WINDS COULD KEEP A CHANCE FOR SHOWERS AND THUNDERSTORMS IN THE
FORECAST. WIND SPEEDS SHOULD REMAIN LIGHT OUTSIDE OF STORMS.
ILM WATCHES/WARNINGS/ADVISORIES
NC...COASTAL FLOOD ADVISORY FROM 8 PM TO 11 PM EDT THIS EVENING FOR
NCZ107.
SC...COASTAL FLOOD ADVISORY FROM 6 PM TO 9 PM EDT THIS EVENING FOR
SCZ054-056.
MARINE...NONE.
WHAT HAS CHANGED...TRA
KEY MESSAGES...TRA
DISCUSSION...TRA
AVIATION...TRA
MARINE...TRA
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