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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 040557
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1255 AM EST WED DEC 4 2013

.SYNOPSIS...
-- Changed Discussion --
AN UPPER LEVEL DISTURBANCE WILL QUICKLY TRACK EAST
ACROSS THE REGION OVERNIGHT... AS A WARM FRONT MOVES NORTHWARD
THROUGH THE AREA. A WARM AND MOIST SOUTHERLY FLOW BEHIND THIS WARM
FRONT WILL PERSIST THROUGH FRIDAY... RESULTING IN ABOVE NORMAL
TEMPERATURES. A COLD FRONT WILL MOVE IN FROM THE WEST EARLY SATURDAY.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 840 PM TUESDAY...

TONIGHT: SURFACE HIGH PRESSURE IS CURRENTLY SHIFTING OFFSHORE THIS
EVENING... RESULTING IN A VERY LIGHT SOUTHERLY RETURN FLOW AT THE
SURFACE. ALOFT... A WEAK MID LEVEL DISTURBANCE IS APPROACHING THE
AREA FROM THE WEST... COUPLED WITH INCREASING SOUTHERLY LOW LEVEL
FLOW JUST ABOVE THE SURFACE WILL HELP TO SUPPORT AT LEAST SOME RAIN
OVERNIGHT ACROSS THE AREA... WITH THE BEST COMBO OF MOISTURE AND
LIFT EXPECTED ACROSS SOUTHERN/EASTERN PORTIONS OF CENTRAL NC.
HOWEVER... STILL NOT EXPECTING MUCH IN THE WAY OF PRECIP... MAYBE A
TENTH OF AN INCH OR SO FOR LOCATIONS THAT SEE THE MOST RAIN. THUS...
WILL SHOW POPS RANGING FORM LOW CHANCE ACROSS OUR FAR NORTH TO LOW
END LIKELY ACROSS OUR FAR SOUTH/SOUTHEAST (ALTHOUGH NOT MUCH
PRECIP).

GIVEN WE ALREADY HAVE DEW POINTS IN THE MID TO UPPER 40S ACROSS THE
AREA AND NO CONTINUED SOURCE OF COLD DRY AIR AT THE SURFACE EXPECT
WE WILL NOT SEE TEMPS FALL TOO MUCH OVERNIGHT FROM CURRENT VALUES.
IN FACT TEMPS HAVE GENERALLY LEVELED OFF INTO THE LOWER TO MID 50S
WITH THE INCREASING CLOUD COVER. EXPECT WE MAY SEE TEMPS DROP A FEW
MORE DEGREES... ESPECIALLY AS PRECIP BEGINS TO MOVE INTO THE AREA...
FIRST ACROSS THE SOUTH/SOUTHWEST (WITHIN THE NEXT HOUR OR TWO)... AS
EVIDENT BY THE LATEST RADAR IMAGES FROM KGSP. FOR NOW WILL CONTINUE
TO GO WITH TEMPS GENERALLY AROUND THE WARM SIDE OF GUIDANCE. THIS
YIELDS LOWS RANGING FROM THE MID 40S NORTH/NORTHEAST TO THE LOWER
50S SOUTHWEST... WITH THE MAIN WARM FRONT EXPECTED TO STILL BE TO
THE SOUTH OF CENTRAL NC BY 12Z WEDNESDAY.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 330 PM TUESDAY...

WEDNESDAY AND WEDNESDAY NIGHT: ALTHOUGH THE LOW AND UPPER LEVEL
MOISTURE AND CLOUDINESS ARE EXPECTED TO STICK AROUND...DRY AIR
SHOULD ADVECT INTO THE MID LEVELS. THE LINGERING LIGHT RAIN IN THE
EAST WEDNESDAY MORNING SHOULD TAPER OFF AND ONLY A SLIGHT CHANCE FOR
RAIN WITH LITTLE IF ANY ACCUMULATION EXPECTED THROUGH WEDNESDAY
EVENING. THE WARM FRONT TO THE SOUTH OF THE AREA TONIGHT SHOULD
START A SLOW NORTHWARD PROGRESSION ON WEDNESDAY...INCREASING THE
SOUTHERLY WARM MOIST ADVECTION INTO CENTRAL NC. AT THE UPPER
LEVELS...EXPECT THE RIDGE TO BUILD OVER THE SOUTHEAST U.S. AS THE
LOW OVER THE MIDWEST MOVES NORTH OVER THE WESTERN GREAT LAKES AND
THE TROUGH AMPLIFIES. DESPITE THE CLOUDINESS EXPECTED...THE WARM
ADVECTION SHOULD BE SUFFICIENT TO YIELD TEMPS QUITE A BIT HIGHER
THAN TODAY AND TONIGHT...HIGHS IN THE LOW 60S NORTH TO UPPER 60S
SOUTH AND EAST WEDNESDAY...LOWS IN THE MID 50S WEDNESDAY NIGHT.

THURSDAY/FRIDAY: WSW FLOW ALOFT ON THE WESTERN PERIPHERY OF AN UPPER
LEVEL RIDGE BUILDING ALONG/JUST OFFSHORE THE EAST COAST WILL GIVE
WAY TO STRENGTHENING SW FLOW ALOFT ACROSS THE CAROLINAS BY FRIDAY AS
AN UPPER LEVEL TROUGH DEEPENS OVER THE ROCKIES/CENTRAL CONUS. IN THE
LOWER LEVELS...A PERSISTENT SOUTHERLY RETURN FLOW /WARM ADVECTION
REGIME/ WILL PREVAIL ON THE WESTERN PERIPHERY OF OFFSHORE HIGH
PRESSURE...WITH INCREASING MOISTURE ACROSS THE CAROLINAS IN THE THU/
FRI TIME FRAME. DESPITE INCREASING CLOUD COVER DOWNSTREAM OF PRECIP
EXPECTED TO DEVELOP ALONG A STRENGTHENING FRONTAL ZONE OVER THE
LOWER MS RIVER VALLEY AND TN/OH VALLEY ON THU/FRI...THERE IS HIGH
CONFIDENCE THAT PERSISTENT WARM ADVECTION WILL RESULT IN A WARMING
TREND EACH DAY...WITH HIGHS RANGING FROM THE UPPER 60S AND LOWER 70S
IN THE NW PIEDMONT TO LOWER/MID 70S IN THE EAST...WARMEST ON FRIDAY
WHEN HIGHS COULD APPROACH THE UPPER 70S IN THE SE COASTAL PLAIN.
EXPECT WARM LOWS IN THE LOWER 60S THU NIGHT GIVEN CLOUD COVER AND A
SOUTHERLY BREEZE /WARM ADVECTION/. EXPECT LITTLE CHANCE FOR PRECIP
THURSDAY/FRIDAY GIVEN FORCING LIMITED TO TRANSIENT SMALL AMPLITUDE
WAVES IN SW FLOW ALOFT AND PERSISTENT WEAK/BROAD WARM ADVECTION.
ASIDE FROM A SMALL CHANCE OF LIGHT RAIN OR SPRINKLES IN THE FAR NW
PIEDMONT LATE THU EVENING THROUGH FRIDAY MORNING...ANTICIPATE PRECIP
LARGELY REMAINING ALONG/WEST OF THE MOUNTAINS. -VINCENT

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 415 PM TUESDAY...

FORECAST CONFIDENCE REMAINS HIGH THAT A STRONG COLD FRONT WILL
PROGRESS THROUGH CENTRAL NC FRIDAY NIGHT AND SATURDAY MORNING...
THOUGH THE PRECISE TIMING OF FROPA WILL HIGHLY DICTATE LOW TEMPS FRI
NIGHT AND HIGHS ON SAT...SO UNCERTAINTY PERSISTS IN THAT REGARD.
UNCERTAINTY ALSO PERSISTS W/REGARD TO PRECIPITATION AMOUNTS. WITHOUT
MUCH IN THE WAY OF UPPER LEVEL FORCING /UNIDIRECTIONAL SW FLOW
ALOFT/...FORCING WILL LARGELY BE TIED TO A PROLONGED PERIOD OF
ISENTROPIC LIFT /WARM ADVECTION/ AS A WARM/MOIST SOUTHWEST H85 FLOW
MOVES ATOP THE SURFACE FRONT TRACKING SOUTHEAST TOWARD THE COAST. AN
UPPER LEVEL TROUGH DIGGING INTO THE 4-CORNERS REGION SAT IS PROGGED
TO TRACK EAST TO THE FRONT RANGE OF THE ROCKIES SAT NIGHT...
AFFECTING THE HEIGHT PATTERN (BACKING/STRENGTHENING LOW-LEVEL FLOW)
OVER THE SOUTHEAST STATES. AS A RESULT...NEAR THE TIME THAT THE H85
TROUGH AXIS WOULD CROSS CENTRAL NC AND WARM ADVECTION ATOP THE
DEVELOPING COLD AIR DAMMING WEDGE WOULD OTHERWISE WEAKEN...
BACKING/STRENGTHENING LOW-LEVEL FLOW OVER THE SOUTHEAST WILL
REINVIGORATE WARM ADVECTION ATOP THE CAD WEDGE...WHICH WILL
STRENGTHEN WITH TIME AS ARCTIC HIGH PRESSURE OVER THE UPPER MIDWEST
BUILDS EASTWARD INTO THE MID-ATLANTIC AND NEW-ENGLAND SAT/SAT
NIGHT...EXTENDING SOUTHWARD INTO THE CAROLINAS EARLY SUNDAY MORNING.

PRECIPITATION CHANCES: FEEL THAT CONFIDENCE IN THE PATTERN IS
SUFFICIENT TO WARRANT A FURTHER INCREASE IN PRECIP CHANCES TO 70%
LATE FRI NIGHT AND SATURDAY. ALTHOUGH A BRIEF LULL IN PRECIP IS
STILL POSSIBLE LATE SAT AFTERNOON (PRIMARILY NORTHERN PIEDMONT)...
THE LATEST GUIDANCE SUGGESTS THAT PRECIP MAY REMAIN MORE-OR-LESS
CONTINUOUS THROUGH SAT NIGHT (PER REASONS IN ABOVE DISCUSSION). THE
UPPER LEVEL WAVE IN THE ROCKIES SAT NIGHT WILL DEAMPLIFY AS IT
TRACKS FROM THE CENTRAL CONUS INTO THE TN VALLEY AND MID-ATLANTIC
SUN/SUN NIGHT...RESULTING IN WEAK MILLER TYPE-B CYCLOGENESIS AND
ISENTROPIC LIFT /WARM ADVECTION/ ATOP THE CAD WEDGE ON SUN...WITH
WARM ADVECTION WEAKENING/SHIFTING NORTHWARD BY LATE SUN...AND PRECIP
CHANCES WILL REMAIN AT 60%. FORECAST CONFIDENCE SIGNIFICANTLY
DEGRADES SUN NIGHT THROUGH EARLY NEXT WEEK W/REGARD TO CAD WEDGE
EROSION AND PRECIP CHANCES...AND WILL MAINTAIN A MOSTLY CLOUDY
FORECAST WITH PRECIP CHANCES AT 20-40%.

TEMPERATURES: TEMPS WILL FALL FROM THE 60S LATE FRI EVENING TO THE
40S FROM NW-SE SATURDAY MORNING THROUGH EARLY SAT AFTERNOON...
FURTHER FALLING INTO THE 30S FROM N-S LATE SAT SAT/NIGHT...THEN
REMAINING STEADY IN THE 30S/40S ON SUN/SUN NIGHT.

WINTER WEATHER ON SUNDAY: LOWS SUN MORNING WILL HIGHLY DEPEND ON THE
PRECISE NATURE OF THE COLD/DRY AIRMASS ADVECTING INTO THE REGION AND
DEGREE OF EVAP COOLING ASSOC/W PRECIPITATION. FROM A PATTERN
RECOGNITION STANDPOINT...PTYPE ISSUES IN THE FORM OF FREEZING RAIN
SHOULD BE AT LEAST A MARGINAL CONCERN ALONG/WEST OF HWY 1 FOR A
PERIOD OF TIME SUNDAY MORNING. MORE SIGNIFICANT ICE ACCUMS CANNOT BE
RULED OUT IN THE FAR N/NW PIEDMONT...HOWEVER...CONFIDENCE REMAINS
VERY LOW IN THE SPECIFICS AT THIS RANGE (TIMING/STRENGTH OF THE SFC
HIGH...PRECIP TIMING/AMOUNTS AND WETBULB POTENTIAL)...AND THE MORE
LIKELY LOCATION FOR SIGNIFICANT ICING POTENTIAL WOULD LIKELY BE
FURTHER NORTH ACROSS WEST/SW VIRGINIA (I.E. SHENANDOAH VALLEY). AT
THIS TIME WILL CONTINUE TO MENTION ALL RAIN SAT NIGHT/SUN DUE TO
GENERAL UNCERTAINTY AT THIS RANGE. -VINCENT

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
AS OF 1255 AM WEDNESDAY...

DETERIORATING AVIATION CONDITIONS ARE LIKELY ACROSS CENTRAL NC EARLY
THIS MORNING... WITH LENGTHY PERIODS OF SUB-VFR CONDITIONS EXPECTED
THROUGH THE END OF THE WEEK. A WARM FRONTAL ZONE TRACKING THROUGH
OUR AREA FROM SW TO NE COMBINED WITH A WEAK DISTURBANCE ALOFT IS
HELPING TO FUEL PATCHY LIGHT RAIN OVER THE REGION WITH
INCREASING/THICKENING CLOUDS. INT/GSO ARE ALREADY MVFR AND ARE
EXPECTED TO DROP TO IFR PRIOR TO DAYBREAK... AND SHOULD REMAIN IFR
THROUGH TODAY (ALTHOUGH CIGS MAY BRIEFLY POP UP ABOVE 1KFT AGL) AND
INTO TONIGHT. FAY/RDU/RWI ARE ALSO EXPECTED TO DROP TO MVFR THEN IFR
BEFORE 09Z... BUT CIGS AT THESE SITES HAVE A BETTER CHANCE OF RISING
BACK UP TO MVFR BY 16Z (RDU/FAY) TO 18Z (RWI). MVFR CIGS/VSBYS ARE
EXPECTED TO DOMINATE AT RDU/FAY/RWI THROUGH 06Z... BUT MAY DROP TO
IFR FOR SHORT PERIODS OF TIME. WINDS ALOFT AT 800-1500 FT AGL WILL
STRENGTHEN FROM THE SW THIS AFTERNOON/TONIGHT TO 20-30 KTS...
CAUSING BORDERLINE LOW LEVEL WIND SHEAR CONDITIONS AFTER NIGHTFALL
TONIGHT AS THE NEAR-SURFACE LAYER STABILIZES WITH SURFACE WINDS
UNDER 6 KTS.

LOOKING BEYOND 06Z TONIGHT...IFR CONDITIONS ARE LIKELY THROUGH
DAYBREAK THU... THEN EXPECT CIGS/VSBYS TO IMPROVE TO VFR BY 16Z THU
WITH BRISK GUSTY SURFACE WINDS FROM THE SW. EXPECT IFR CONDITIONS TO
RETURN THU EVENING/NIGHT WITH LOW STRATUS AND FOG... LIFTING TO MVFR
THEN VFR BY LATE MORNING FRI. SUB-VFR CONDITIONS (POTENTIALLY
IFR/LIFR) ARE LIKELY TO DOMINATE FROM FRIDAY EVENING THROUGH SUNDAY
AS A COLD FRONT MOVES IN AND STALLS OVER THE AREA. COOL SATURATED
SURFACE AIR WITH A STRONG INVERSION IN THE LOWEST 4KFT AGL WILL LEAD
TO A SHARP SHIFT IN WIND SPEED AND DIRECTION THROUGH A SHALLOW LAYER
WITHIN THE LOWEST 4KFT AGL SAT THROUGH SUN... WHICH MAY POSE A
HAZARD TO PILOTS... PARTICULARLY OF SMALL AIRCRAFT... OVER THE
WEEKEND. -GIH
-- End Changed Discussion --
&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

SYNOPSIS...HARTFIELD
NEAR TERM...BSD
SHORT TERM...KC/VINCENT
LONG TERM...VINCENT
AVIATION...HARTFIELD/ELLIS