685
FXUS62 KRAH 151801
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
101 PM EST SUN DEC 15 2024
SYNOPSIS
A SHORTWAVE TROUGH WILL GLANCE VA AND NORTHWESTERN NC THIS MORNING.
HIGH PRESSURE AND ASSOCIATED COLD AIR DAMMING WILL OTHERWISE EXTEND
ACROSS THE PIEDMONT OF THE CAROLINAS, WHILE GRADUALLY WEAKENING,
THROUGH TUESDAY, DURING WHICH TIME A QUASI-STATIONARY, WEDGE FRONT
WILL WAVER OVER THE EASTERN PIEDMONT AND COASTAL PLAIN.
NEAR TERM /THROUGH TONIGHT/
AS OF 940 AM SUNDAY...
NO MAJOR CHANGES WERE MADE WITH THE MID-MORNING FORECAST UPDATE AS
THE FORECAST REMAINS ON TRACK BASED ON INCOMING OBSERVATIONS AND
LATEST HI-RES GUIDANCE. PREVIOUS FORECAST DISCUSSION AS OF 410 AM
FOLLOWS.
ALREADY STRONG WARM AIR ADVECTION, AMID ESELY FLOW CENTERED AT 925
MB --AND ASSOCIATED ISENTROPIC UPGLIDE ATOP AN ANOMALOUSLY STRONG
SURFACE HIGH EXTENDING THROUGHOUT THE ERN US-- WILL FURTHER
STRENGTHEN TODAY. THAT ISENTROPIC UPGLIDE, IN CONJUNCTION WITH
UPSLOPE FLOW ACROSS WRN NC, WILL CONTRIBUTE TO THE EXPANSION OF LOW
CEILINGS AND DEVELOPMENT OF LIGHT RAIN AND DRIZZLE INTO THE NW NC
PIEDMONT TODAY. A TIGHT TEMPERATURE GRADIENT AND WEDGE FRONT WILL
DEVELOP ALONG THE ERN EDGE OF THE ASSOCIATED CLASSICAL, DIABATICALLY-
ENHANCED COLD AIR DAMMING AIRMASS OVER THE NW PIEDMONT, WITH HIGH
TEMPERATURES THAT WILL RANGE SHARPLY FROM AROUND 40 F AT INT TO LWR
60S IN THE SRN-CNTL COASTAL PLAIN.
TONIGHT, THE AFOREMENTIONED INTENSE WAA REGIME WILL GRADUALLY
WEAKENS AT 925 MB, EDGE EWD, AND BECOME MAXIMIZED AROUND 850 MB.
NOCTURNAL COOLING/INCREASING BOUNDARY LAYER HUMIDITY TONIGHT WILL
LIKELY OFFSET THE LIFTING (IN HEIGHT) OF THE WAA AND ASSOCIATED
FORCING FOR ASCENT, SUCH THAT LOW CEILINGS AND AREAS OF LIGHT RAIN
AND DRIZZLE WILL DEVELOP/SPREAD EWD ACROSS ALL OF CNTL NC OVERNIGHT.
LIMITED DIURNAL TEMPERATURE RANGE WITHIN THE HEART OF THE CAD WILL
FAVOR JUST A 2-3 F DECREASE IN TEMPERATURES INTO THE UPR 30S OVER
THE NW PIEDMONT, WITH MORE APPRECIABLE COOLING INTO THE 40S --WITH
ASSOCIATED FURTHER EWD DEVELOPMENT/EXPANSION OF THE CAD AIRMASS
THROUGHOUT CNTL NC-- WILL RESULT THROUGH MON MORNING.
SHORT TERM /MONDAY AND MONDAY NIGHT/
AS OF 320 AM SUNDAY...
SOME REMNANTS OF TODAY'S COLD-AIR DAMMING/HIGH PRESSURE WILL REMAIN
ACROSS CENTRAL NORTH CAROLINA MONDAY MORNING, BUT THINK THAT ANY
REMAINING SHOWERS SHOULD BE LIMITED TO FAR NORTHEASTERN COUNTIES AND
END BY MID-MORNING. MODELS TYPICALLY ERODE CAD TOO QUICKLY, AND AS A
RESULT, CONFIDENCE ON MONDAY'S HIGH TEMPERATURES IS LOW AS THE
TEMPERATURE FORECAST WILL BE HIGHLY DEPENDENT ON HOW LONG IT TAKES
FOR CLOUD COVER TO BREAK. THE CURRENT FORECAST CALLS FROM A RANGE
FROM THE LOWER 50S IN THE NORTHWEST TO THE UPPER 60S IN THE
SOUTHEAST, WHERE THE MOST SUN WILL OCCUR. A COLD FRONT WILL CROSS
THE APPALACHIAN MOUNTAINS LATE MONDAY INTO MONDAY NIGHT, AND IT
APPEARS THAT MOST OF THE MOISTURE IN THE ATMOSPHERE SHOULD BE
SQUEEZED OUT ON THE WESTERN SIDE OF THE MOUNTAINS. HAVE ONLY GONE
WITH SLIGHT CHANCE SHOWERS NORTHWEST OF RALEIGH AFTER MIDNIGHT. LOWS
WILL RANGE FROM THE MID 40S TO THE MID 50S.
LONG TERM /TUESDAY THROUGH SATURDAY/
AS OF 320 AM SUNDAY...
HAVE GONE AHEAD AND REMOVED ANY CHANCE OF SHOWERS TUESDAY MORNING AS
MODELS CONTINUE TO SHOW MINIMAL MOISTURE LOCALLY AS THE COLD FRONT
MOVES THROUGH THE REGION. THE GFS AND ECMWF MODEL SOLUTIONS FOR THE
NEXT STORM SYSTEM TUESDAY NIGHT THROUGH THURSDAY HAVE BEGUN TO
CONVERGE A BIT IN THEIR SOLUTIONS, BUT THIS PART OF THE FORECAST
STILL HAS SLIGHTLY BELOW NORMAL CONFIDENCE CONSIDERING THE
DIFFERENCE IN THE TRACKS OF THE SURFACE LOW. WHILE BOTH MODELS SHOW
A LOW OVER KENTUCKY WEDNESDAY MORNING THAT WILL TRACK OFF THE NEW
ENGLAND COAST THURSDAY MORNING, THE EUROPEAN REMAINS SLIGHTLY
FARTHER TO THE SOUTHEAST THAN THE GFS, WHICH SHIFTS THE TIME PERIOD
OF RAIN QUICKER THAN THE GFS. THE GENERAL CONSENSUS IS THAT THE
HIGHEST CHANCE OF SHOWERS WILL COME WITH THE COLD FRONTAL PASSAGE
WEDNESDAY NIGHT, AND HAVE CONTINUED LIKELY POPS AT THAT TIME. THE
00Z DETERMINISTIC RUNS OF THE MODELS DRY OUT CENTRAL NORTH CAROLINA
BY THURSDAY MORNING, WHILE THE ENSEMBLES KEEP SHOWERS IN FOR A BIT
ON THURSDAY. WILL KEEP SOME POPS IN THE FORECAST DURING THE DAY, BUT
REDUCE THEM FROM WHAT WAS INHERITED. AS HIGH PRESSURE MOVES TO THE
EAST, THE REST OF THE FORECAST SHOULD BE DRY.
TEMPERATURES SHOULD BE ABOVE NORMAL TUESDAY AND WEDNESDAY, WITH
SOUTHERN LOCATIONS IN THE 70S, BEFORE TEMPS TRANSITION TO NEAR
NORMAL ON THURSDAY BEHIND THE COLD FRONT AND FALL BELOW NORMAL FOR
FRIDAY AND SATURDAY. TEMPERATURES WILL NOT FALL BELOW FREEZING UNTIL
WELL AFTER PRECIPITATION ENDS, SO ALL PRECIPITATION WILL FALL AS
RAIN.
AVIATION /18Z SUNDAY THROUGH FRIDAY/
AS OF 100 PM SUNDAY...
IFR CIGS IN THE NC FOOTHILLS HAVE BRIEFLY LEAKED INTO INT WITH MVFR
CIGS FROM GSO TO JUST WEST OF RDU AND VFR ELSEWHERE. CIGS IN THE
TRIAD MAY BOUNCE AROUND FROM THEIR STARTING 18Z OBS, BUT AS AN AREA
OF RAIN OVER UPSTATE SC MOVES NE THROUGH THE AFTERNOON, CIGS WILL
LOWER TO IFR. AFTER SUNSET, NOCTURNAL COOLING AND INCREASING
BOUNDARY LAYER HUMIDITY WILL SUPPORT IFR CIGS TO OOZE EASTWARD AND
LOWER TO LIFR IN MOST LOCATIONS. SOME AIRPORT MINIMUMS MAY BE
REACHED BY MON MORNING AS CIGS LOWER AND BEGIN TO REDUCE VSBY AT THE
SURFACE. GRADUAL IMPROVEMENT THROUGH MON MORNING TO VFR AT RWI/FAY
FIRST AND PERHAPS RDU, BUT THE TRIAD TERMINALS WILL LIKELY REMAIN
BELOW ALTERNATE MINIMUMS (< 600 FT) THROUGH THE TAF PERIOD.
OUTLOOK: FLIGHT RESTRICTIONS AT INT/GSO WILL LIKELY FLUCTUATE
BETWEEN IFR-MVFR BY DAY AND LIFR-IFR BY NIGHT THROUGH WEDNESDAY
MORNING, AS COLD AIR DAMMING HOLDS OVER THE NW NC PIEDMONT.
MEANWHILE TO THE EAST, FLIGHT RESTRICTIONS ARE LIKELY TO BE CONFINED
MAINLY TO THE LATE NIGHT-MORNING HOURS. LOW-LEVEL WIND SHEAR WILL
ALSO BE POSSIBLE OVER THE PIEDMONT MON NIGHT. THE NEXT EXTENDED
PERIOD OF VFR CONDITIONS THROUGHOUT CNTL NC LIKELY WILL NOT BEGIN
UNTIL ANOTHER FRONTAL SYSTEM MOVES ACROSS THE REGION, WITH FOLLOWING
DRY AIR, WED NIGHT-THU.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...MWS
NEAR TERM...MWS/SWIGGETT
SHORT TERM...GREEN
LONG TERM...GREEN
AVIATION...SWIGGETT/MWS
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