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000
FXUS62 KRAH 112331
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
631 PM EST WED DEC 11 2013

.SYNOPSIS...
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HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST
TONIGHT THROUGH FRIDAY. A WEAK LOW PRESSURE SYSTEM WILL DEVELOP IN
THE DEEP SOUTH FRIDAY NIGHT...THEN TRACK NORTHEAST ALONG THE
CAROLINA AND MID ATLANTIC COAST ON SATURDAY AND SUNDAY.
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&&

.NEAR TERM /TONIGHT THROUGH THURSDAY NIGHT/...
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AS OF 240 PM WEDNESDAY...

WEAK HIGH PRESSURE CENTERED OVER EASTERN NC WILL PUSH OFFSHORE
TONIGHT...WITH A WEAK RETURN FLOW DEVELOPING AHEAD OF ANOTHER SHOT
OF COLD AIR LATER TONIGHT. DEWPOINTS HAVE TEMPORARILY MIXED OUT
LOWER THAN MOST GUIDANCE VALUES IN THE WESTERN PIEDMONT...SO WILL
ADJUST THOSE WITH THE FORECAST PACKAGE.

TONIGHT...A DRY COLD FRONT...CURRENTLY STRETCHING FROM MICHIGAN TO
MISSOURI...WILL CROSS THE AREA TONIGHT BETWEEN 03Z AND
09Z...USHERING ANOTHER SHOT OF ARCTIC AIR. WITH LOW LEVEL
THICKNESSES DROPPING TO AROUND 1280M BY 12Z...GUIDANCE IS GIVING MID
TO UPPER 20S...WITH A FEW AREAS ACROSS THE NORTH POSSIBLY DIPPING
BELOW 25.

THURSDAY AND THURSDAY NIGHT...A COLD NORTHWESTERLY WIND WILL LIKELY
BE A LITTLE GUSTY IN THE MORNING...MAINLY IN THE 15-20KT
RANGE...BEFORE ABATING LATER IN THE DAY AS CANADIAN HIGH PRESSURE
BUILDS IN FROM THE WEST-NORTHWEST.  PATTERN RECOGNITION SUGGESTS
OROGRAPHIC CIRRUS MAY DEVELOP EARLY IN THE DAY...THOUGH THE GFS IS
THE ONLY MODEL SHOWING MORE SIGNIFICANT SATURATION WRT ICE. THE
MOUNTAIN WAVE SIGNAL IS EVIDENT ON THE NAM AND ECMWF...SO IT WILL
DEPEND ON WHERE THE UPSTREAM MOISTURE CHANNEL ADVECTS. NOT CONFIDENT
ENOUGH IN CIRRUS TO ALTER HIGHS SO WILL MAINLY STATISTICAL
GUIDANCE...40-46. LOWS WILL BE COLDER ON THURSDAY NIGHT AS THE
SURFACE HIGH SETTLES OVER THE REGION...LIKELY IN THE LOWER TO MID 2OS
AREA WIDE.
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&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
AS OF 240 PM WEDNESDAY...

FOR FRI/FRI NIGHT: QUIET WEATHER FRI WITH HIGH PRESSURE OVERHEAD TO
START THE DAY. THE MID LEVEL LOW NOW OFF THE SRN CA/BAJA COAST WILL
OPEN UP AND EJECT EASTWARD THU... REACHING OK/TX LATE FRI... AS A
ANOTHER NRN-STREAM WAVE TRACKS CLOSE ON ITS HEELS. MID LEVEL FLOW
ALOFT OVER THE CAROLINAS TRANSITIONS QUICKLY FRI FROM WEAKLY/
BROADLY ANTICYCLONIC TO AN ACCELERATED FLAT SW FLOW... AND MODELS
ARE IN AGREEMENT SHOWING THICKENING HIGH CLOUDS DURING THE
AFTERNOON. THE SURFACE HIGH SHIFTS QUICKLY OFFSHORE FRI AFTERNOON
WITH A WEAK INVERTED TROUGH DEVELOPING JUST OFF THE COAST... AS
ATLANTIC-SOURCE RETURN FLOW RAMPS UP OVER THE CWA. THE AFFECTS OF
THIS APPEAR TO HOLD OFF UNTIL MAINLY AFTER MIDNIGHT HOWEVER... AS
THE SUBCLOUD LAYER (BELOW 700 MB) REMAINS DRY UNTIL THEN. CURRENT
FORECAST DEPICTS THIS WELL AND WILL STICK WITH A RAPID INCREASE IN
CLOUDS LATE FRI... AND OVERCAST SKIES FRI NIGHT AS THE DAMPENING
LEAD WAVE MOVES INTO THE REGION FROM THE WSW (WHILE THE TRAILING
PRIMARY TROUGH DIGS ACROSS NM/W TX) IN CONJUNCTION WITH LOW LEVEL
SATURATION. A RESIDUAL LOW LEVEL STABLE LAYER HOLDS OVER CENTRAL NC
FRI NIGHT... AND THE INCREASING MOIST UPGLIDE OVERRUNNING THIS LAYER
SHOULD HELP LOCK IN THE STABLE POOL AREAWIDE (AT LEAST INITIALLY).
LATEST MODEL RUNS SUPPORT A SLOWER ARRIVAL TO THE PRECIP... WITH THE
ECMWF/NAM HOLDING IT JUST TO OUR WEST THROUGH 12Z SAT... WHILE THE
GFS BRINGS IN ONLY VERY LIGHT AMOUNTS... AND WILL HOLD ONTO LOW
CHANCE POPS VERY LATE FRI NIGHT IN THE WRN HALF ONLY. SURFACE WET
BULB FORECASTS FROM THE NAM AND GFS SIT VERY CLOSE TO 32F OVER THE
NW AND FAR NRN PIEDMONT AS DAYBREAK APPROACHES SAT... AND WITH THE
MAX TEMP IN THE WARM NOSE ALOFT GETTING UP TO 5+ C... WE COULD SEE A
LITTLE NUISANCE FREEZING RAIN IN THE NW PIEDMONT WITH ANY PRECIP
THAT CAN MANAGE TO MAKE IT TO THE GROUND VERY LATE FRI NIGHT.
HOWEVER IT LOOKS LIKE ANYTHING THAT FALLS WILL BE VERY LIGHT WITH
THE SUBSTANTIAL RAINFALL HOLDING OFF UNTIL WELL AFTER SUNRISE. HIGHS
48-51 FRI. LOWS 31-37.

FOR SAT THROUGH SUN NIGHT: HIGH CONFIDENCE IN HIGH RAIN CHANCES SAT
INTO SUN MORNING... AS THE SECONDARY MID LEVEL TROUGH PROGRESSES
EASTWARD TOWARD NC. AS HIGH-PW AIR SURGES NORTHEASTWARD INTO NC
(ANTICIPATED VALUES OF 1.0-1.5 INCHES WILL EXCEED 200% OF NORMAL)...
FORCING FOR ASCENT WILL STRENGTHEN QUICKLY AND THROUGH A DEEP
LAYER... WITH SEVERAL LIFT MECHANISMS AT PLAY INCLUDING MID LEVEL
DPVA... INCREASING UPPER DIVERGENCE FROM SW TO NE AS THE UPPER JET
FROM THE LOWER MISS VALLEY TO OFF DELMARVA STRENGTHENS TO OVER 140
KTS... AND STRENGTHENING/ DEEPENING MOIST UPGLIDE. WILL RETAIN THE
CATEGORICAL POPS... STARTING LATE MORNING SAT... AND EXTENDING
THROUGH SAT NIGHT BEFORE ENDING SLOWLY WEST TO EAST SUN MORNING AS
THE MID LEVEL TROUGH SLIDES THROUGH. MODELS ARE IN EXCELLENT
AGREEMENT ON THE FORMATION OF THE LOW LEVEL IN SITU WEDGE PATTERN ON
SAT... AS THE RAINFALL OVERRIDES THE COOL STABLE SURFACE-BASED POOL
DEPOSITED BY THE OFFSHORE-DRIFTING HIGH. MODEL SOLUTIONS ARE QUITE
CLOSE WITH THE SURFACE PATTERN... TAKING THE PRIMARY LOW ACROSS
LA/MS/AL/GA SAT WITH AN INVERTED TROUGH TO JUST W OF THE MOUNTAINS
(AND DIMINISHING LOW TO THE ERN OH VALLEY)... WHILE THEY PUSH THE
WEDGE FRONT ABOUT AS FAR INLAND AS THE TRIANGLE AREA BY LATE SAT.
IT IS DIFFICULT TO PREDICT AT THIS TIME RANGE EXACTLY WHERE THE WEDGE
FRONT WILL SET UP... BUT THE MODEL AGREEMENT INCREASES CONFIDENCE.
THE TEMP SPREAD EITHER SIDE OF THIS LINE COULD EASILY BE 20 DEGREES
OVER A SHORT DISTANCE ORTHOGONAL TO THE WEDGE FRONT. LATEST GUIDANCE
AND CLIMATOLOGY STILL SUPPORTS HIGHS RANGING FROM THE LOW-MID 40S NW
TO THE LOW-MID 60S IN THE FAR SE. LATEST GUIDANCE IS FAIRLY CLOSE ON
AMOUNTS AS WELL... INDICATING ABOUT A HALF TO THREE-QUARTERS OF AN
INCH FOR THE EVENT... WHICH SEEMS REASONABLE GIVEN THE HIGH WATER
CONTENT AND SPEED OF THIS SYSTEM. A FEW LOW-TOPPED ROTATING STORMS
REMAIN POSSIBLE SAT AFTERNOON INTO THE EVENING... AS A THIRD LOW IS
EXPECTED TO FORM ALONG THE WEDGE BOUNDARY SOMEWHERE OVER CENTRAL NC
LATE SAT BEFORE ZIPPING NORTHEASTWARD THROUGH THE EVENING.

KINEMATICS REMAIN IMPRESSIVE WITH FORMIDABLE LOW LEVEL HELICITY OVER
300 M2/S2 AND OVER 30 KTS OF 0-2 KM SHEAR... BUT FORECAST SOUNDINGS
SHOW JUST 100-200 J/KG OF MOSTLY ELEVATED CAPE AT BEST... SO ANY
CELLS WOULD NEED TO RELY ON STRONG DYNAMIC LIFT IN CONJUNCTION WITH
THE WEAK INSTABILITY TO GET ANY SUBSTANTIAL TILTING AND STRETCHING
OF LOW LEVEL VORTICITY. THIS SHEAR IS LIKELY TO DROP DRAMATICALLY AS
THE LOW TRACKS TO OUR NE PRIOR TO MIDNIGHT SAT NIGHT. RAIN CHANCES
WILL DIMINISH SUN MORNING WITH FALLING PW BEHIND THE EXITING 850 MB
FRONT... ALTHOUGH THE MID LEVEL TROUGH DOES NOT PASS THROUGH UNTIL
LATER IN THE DAY... SO WE SHOULD CONTINUE TO SEE HIGH CLOUDS THROUGH
THE DAY. IN ADDITION... THERE IS A LACK OF STRONG LOW LEVEL
DOWNSLOPE FLOW THROUGH SUN WITH A LINGERING SURFACE TROUGH
STRETCHING BACK THROUGH WRN NC... SO WE SHOULD SEE SOME SCT-BROKEN
STRATOCUMULUS PERSIST AS WELL... ALL YIELDING PARTLY CLOUDY SKIES.
MODELS SHOW A BACKDOOR SURFACE TROUGH DROPPING SSW THROUGH NC SUN
NIGHT WITH FORECAST SOUNDINGS DEPICTING QUITE A BIT OF MOISTURE IN
THE LOWEST 50 MB WITH NE FLOW DEVELOPING AS HIGH PRESSURE TRIES TO
BUILD IN FROM THE W AND SW OVERNIGHT... SO WILL INDICATE AT LEAST
PARTLY CLOUDY SKIES THROUGH SUN NIGHT. LOWS FROM 37-50 SAT NIGHT...
HIGHS SUN 49-56 WITH ABOVE-NORMAL THICKNESSES NOT FALLING UNTIL LATE
SUN. LOWS 26-32.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 240 PM WEDNESDAY...

A DRY MEAN AIR MASS IS FORECAST FOR THIS PART OF THE FORECAST
PERIOD. THE GFS HAS BEEN CONSISTENT WITH A BROAD WEST-SOUTHWEST TO
EAST FLOW FROM THE WESTERN STATES THROUGH THE EASTERN CONUS...WITH
ONLY MODEST WEAKNESS IN THE WESTERLY FLOW ALOFT AS A DRY COLD FRONT
MOVES THROUGH CENTRAL NORTH CAROLINA WEDNESDAY. MID-LEVEL MOISTURE
REMAINS NORTH OF CENTRAL NORTH CAROLINA...CLOSER TO THE MODESTLY
BETTER FORCING ALOFT. ALMOST ALL OF THE OTHER GUIDANCE...NOTABLY THE
LATEST CANADIAN...DGEX...AND ECMWF...ARE STRONGER AND DEEPER WITH A
MID-LEVEL TROUGH MOVING OUT OF THE GREAT LAKES TOWARD THE MID-
ATLANTIC DURING THE MIDDLE OF NEXT WEEK...WITH A SLIGHTLY FASTER
SURFACE FRONTAL PASSAGE ON THE 12Z ECMWF. THESE DEEPER GUIDANCE
STILL SUGGEST DRY CONDITIONS...BUT WITH POSSIBLY LIGHT QPF INTO THE
MOUNTAINS DIMINISHING AS ENERGY CROSSES THE HIGHER TERRAIN. FOR THIS
FORECAST...WILL CONTINUE A DRY FORECAST...NOTING A GENERAL PARTLY
CLOUDY CONDITION ESPECIALLY TUESDAY INTO WEDNESDAY. ALL MEX MOS
GUIDANCE POPS ARE BELOW CLIMATOLOGY FROM THE DAY MONDAY THROUGH
WEDNESDAY...ALONG WITH THE LATEST ECMWF ENSEMBLE MEAN MOS POPS.

THE CONSENSUS OF 1000-850MB THICKNESSES SUPPORT HIGH TEMPERATURES
ABOVE THE MOS GUIDANCE. THE GFS MEX MOS TREND IS COOLER BY ABOUT A
CATEGORY ESPECIALLY EARLY IN THIS PERIOD...CLOSE TO THE ECMWF
ENSEMBLE MEAN. WILL TREND WARMER FROM THE PREVIOUS FORECAST...CLOSER
TO THE GUIDANCE BUT NOT QUITE AS WARM AS WHAT THE THICKNESSES WOULD
SUPPORT...IN CONJUNCTION WITH HPC GUIDANCE. THE 12Z ECMWF...WITH A
DEEPER MID-LEVEL TROUGH AND FASTER SURFACE FRONTAL PASSAGE...WOULD
FAVOR HIGHS NOT QUITE TO THE LEVEL SUPPORTED BY THE CONSENSUS OF
1000-850MB THICKNESSES. BOTH HIGHS AND LOWS WILL BE FORECAST AT OR
SLIGHTLY BELOW NORMAL.

&&

.AVIATION /00Z THURSDAY THROUGH SUNDAY/...
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AS OF 630 PM WEDNESDAY...

24-HR TAF PERIOD: VFR CONDITIONS WILL RULE THROUGH THE TAF PERIOD IN
ASSOCIATION WITH HIGH PRESSURE BUILDING INTO THE REGION FROM THE
WEST. LIGHT NNW/NW OR VARIABLE WINDS TONIGHT WILL BECOME NORTH-
NORTHWEST AT 8-12 KT (GUSTS UP TO 15-20 KT) AFTER SUNRISE...OR
BETWEEN 12-15Z THU. NNW WINDS WILL GRADUALLY DECREASE TO 5-8 KT BY
LATE THU AFTERNOON...EVENTUALLY GOING CALM THU NIGHT.

LOOKING AHEAD: VFR/DRY CONDITIONS ARE EXPECTED TO PREVAIL THROUGH
FRI AS HIGH PRESSURE BUILDS OVER THE REGION. WIDESPREAD ADVERSE
AVIATION CONDITIONS ARE EXPECTED OVER THE WEEKEND (SAT/SUN) IN
ASSOCIATION WITH A GOMEX LOW PRESSURE SYSTEM TRACKING NORTHEAST
ALONG THE CAROLINA/MID-ATLANTIC COAST.-VINCENT
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&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...SMITH
SHORT TERM...HARTFIELD
LONG TERM...DJF
AVIATION...VINCENT