-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 100835
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
335 AM EST TUE DEC 10 2013

.SYNOPSIS...AN AREA OF LOW PRESSURE WILL CROSS CENTRAL NC
TODAY...DRAGGING A COLD FRONT ACROSS THE AREA THIS AFTERNOON. COOL
AND DRY HIGH PRESSURE WILL EXTEND INTO THE CAROLINAS AND VIRGINIA
WEDNESDAY THROUGH FRIDAY.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 305 AM TUESDAY...

THIS MORNING AND TODAY: LINGERING CAD AIRMASS CONTINUES TO HANG ON
THIS MORNING ALONG WITH A PLUME OF MOISTURE IN THE SW FLOW ALOFT
HELPING TO SPREAD RAIN ACROSS ALL OF CENTRAL NC... EXCEPT FOR THE
FAR NORTHWEST PIEDMONT CURRENTLY. THIS HAS HELPED IN KEEPING DENSE
FOG FROM DEVELOPING THIS MORNING FOR MOST LOCATIONS. WITH THE 4 AM
PACKAGE WE PLAN ON DROPPING THE DFA FOR THE NORTHWEST PIEDMONT AS
MID AND HIGH LEVEL CLOUD COVER ASSOCIATED WITH THE S/W PRODUCING
RAIN JUST TO THE EAST OF THE NORTHWEST PIEDMONT HAS ALLOWED VISBYS
TO IMPROVE GREATLY OVER THE PAST FEW HOURS. HOWEVER... AT PATCHY
FOR/DENSE FOG WILL REMAIN POSSIBLE IN BETWEEN THIS AREA OF RAIN AND
RAIN EXPECTED TO MOVE INTO THE AREA FROM THE WEST LATER THIS
MORNING. ALTHOUGH CONFIDENCE IN THE FOG AND HOW DENSE IS QUITE LOW.

LATER THIS MORNING WE WILL SEE THE NEXT AREA OF RAIN AND EVEN SOME
EMBEDDED THUNDER (CURRENTLY LOCATED TO THE WEST OF CENTRAL NC FROM
THE NORTHERN GULF COAST TO THE CENTRAL APPALACHIAN) MOVE INTO THE
AREA THIS MORNING INTO THE AFTERNOON AS A STRONG QUICK MOVING S/W
MOVES FROM THE PLAINS/MIDWEST THIS MORNING INTO THE NORTHEAST/NEW
ENGLAND BY THIS EVENING. THIS S/W WILL HELP DRIVE A COLD FRONT
THROUGH CENTRAL NC TODAY AND FINALLY SCOUR OUT THE CAD AIRMASS BY
MID TO LATE AFTERNOON TODAY... WITH MOST EVERYBODY SEEING SOME SUN
BY LATE IN THE DAY (CLEARING IN A WEST TO EAST FASHION). THIS WILL
MAKE FOR A CHALLENGING TEMP FORECAST FOR TODAY. IN FACT A WEAK AREA
OF LOW PRESSURE IS LOCATED ALONG THE SOUTHERN/SOUTHEASTERN REACHES
OF THE WEDGE FRONT NEAR KCAE. AS THIS LOW SLOWLY LIFTS NNE IT MAY
HELP DRAG THE WEDGE FRONT BACK NORTHWESTWARD INTO OUR FAR SOUTHEAST
COUNTIES... ALLOWING THEM TO WARM UP INTO THE 60S. HOWEVER... FOR
LOCATIONS THAT REMAIN IN THE WEDGE AIRMASS... WE DO NOT EXPECT MUCH
MOVEMENT IN THE TEMPS UNTIL THE COLD FRONT MOVES ACROSS THE REGION
TO SCOUR OUT THE CAD AIRMASS. IN FACT WE MAY SEE TEMPS ACTUALLY RISE
BY SEVERAL DEGREES WHEN THE SKIES CLEAR OUT LATE IN THE DAY WITH THE
NORTHWESTERLY DOWNSLOPE FLOW (WARMING ONLY IN THE REGION THAT REMAIN
IN THE CAD UNTIL FROPA). THUS... EXPECT HIGH TEMPS WILL RANGE FROM
THE MID TO UPPER 40S IN THE CAD AIRMASS TO THE MID TO UPPER 60S IN
THE FAR SOUTHEAST.

TONIGHT: HIGH PRESSURE WILL BUILD INTO THE AREA... WITH A BREEZE TO
START THE NIGHT. THE MSLP WEAKENS NEAR DAYBREAK ALLOWING TEMPS TO
DROP NICELY AFTER MIDNIGHT TONIGHT. EXPECT LOW TEMPS WILL RANGE FROM
THE LOW TO MID 20S IN THE USUAL RURAL COLD AREAS TO AROUND 30 SE.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 250 AM TUESDAY...

WEDNESDAY THROUGH FRIDAY...A BROAD UPPER LEVEL TROUGH WILL COVER THE
EASTERN TWO-THIRDS OF THE NATION THIS PERIOD WITH A SPLIT FLOW
REGIME ALOFT. THE NORTHERN STREAM WILL BE THE MORE DOMINANT JET THIS
PERIOD...WHICH WILL KEEP THE MAIN STORM TRACK WELL TO OUR NORTH-
NORTHWEST.

CLOSER TO THE SURFACE...A PAIR OF HIGH PRESSURE SYSTEMS WILL
INFLUENCE OUR WEATHER. THE FIRST...OF CONTINENTAL ORIGIN WILL RESIDE
OVER THE MID ATLANTIC WEDNESDAY THEN SCOOT OFFSHORE BY WEDNESDAY
EVENING. AIR MASS ASSOCIATED WITH THIS HIGH DRIER AND RELATIVELY
COLL WITH THIS TIME OF YEAR BUT NOT BITTERLY COLD. THICKNESSES
WEDNESDAY AFTERNOON AVERAGE ABOUT 15M BELOW NORMAL...SUGGESTING MAX
TEMPS ABOUT 2-3 DEGREES BELOW NORMAL. EXPECTING AT A MINIMUM PARTLY
CLOUDY SKIES ACROSS THE AREA SO SHOULD HAVE SUFFICIENT WARMTH FROM
THE SUN. MOS GUIDANCE IN LINE WITH THIS THINKING SUGGESTING MAX
TEMPS UPPER 40S NW TO LOWER 50S SE.

A WEAK SFC FRONT WILL SWEEP ACROSS THE REGION WEDNESDAY NIGHT...IN
ADVANCE OF ANOTHER HIGH PRESSURE SYSTEM...THIS ONE OF CANADIAN
ORIGIN. THE FRONTAL PASSAGE WILL BE UNEVENTFUL...MAINLY JUST A
WINDSHIFT AND A FEW PASSING CLOUDS. NLY WINDS THURSDAY WILL ADVECT
COLDER AIR INTO CENTRAL NC WITH THICKNESSES THURSDAY AFTERNOON ABOUT
50M BELOW NORMAL. FAVOR THE COLDER NAM MOS GUIDANCE WHICH IS 3-5
DEGREES COLDER THAN THE GFS MOS.  MAX TEMPS THURSDAY NEAR 40 FAR
NORTH-NW TO THE MID 40S SOUTH.

THIS HIGH WILL SETTLE OVERHEAD THURSDAY NIGHT....PROVIDING US WITH
THE COLDEST NIGHT DURING THIS PERIOD. UNDER CLEAR SKIES AND A NEAR
CALM SFC WIND...TEMPS WILL FALL QUICKLY AFTER SUNSET. THICKNESSES IN
THE 1275-1290M RANGE HAVE HISTORICALLY RESULTED IN MIN TEMPS IN THE
MID 20S WITH NEAR 20-LOWER 20S IN THE MORE RURAL/SHELTERED AREA.
WILL FOLLOW THIS SCENARIO.

A MODEST WARM-UP OCCURS FRIDAY AS THE AIR MASS MODIFIES AND THE
PARENT HIGH SCOOTS OFFSHORE BY AFTERNOON. THIS RETURN FLOW WILL
ADVECT A MOIST AND WARMER AIR MASS INTO OUR REGION BY LATE FRIDAY.
THIS MOISTURE ADVECTION WILL BE EVIDENT BY AN INCREASE IN MID-HIGH
LEVEL CLOUDS LATE IN THE DAY FROM THE WEST-SW. AFTERNOON TEMPS IN
THE 40S TO NEAR 50 SHOULD BE COMMON.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
-- Changed Discussion --
AS OF 335 AM TUESDAY...

FRIDAY NIGHT THROUGH SATURDAY NIGHT... MODEL GUIDANCE CONTINUES TO
SUGGEST AN UNSETTLED WEATHER REGIME THIS PERIOD THOUGH MODELS DIFFER
ON TIMING AS WELL AS STRENGTH OF SURFACE ELEMENTS/PARAMETERS.

THE HIGH PRESSURE SYSTEM OVERHEAD FRIDAY WILL SCOOT EASTWARD AFTER
DEPOSITING A COOL DRY AIR MASS AT THE SURFACE. THE RETURN FLOW ALOFT
WILL ADVECT WARM MOIST AIR UP AND OVER THIS COOL STABLE DOME LATE
FRIDAY NIGHT INTO SATURDAY. SURFACE PRESSURE PATTERN SUGGEST A COLD
AIR DAMMING EVENT (MOST LIKELY AN INSITU RATHER THAN HYBRID AS
APPEARS CENTRAL NC NOT ABLE TO CONNECT TO ANOTHER HIGH LOCATED OVER
SOUTHERN QUEBEC).

MODEL DIFFERENCES BECOME MORE NOTICEABLE SATURDAY AS GFS MORE
AGGRESSIVE SPREADING PRECIP NWD ACROSS THE REGION (VERSUS THE ECMWF)
PLUS IT IS QUICKER/DEEPER WITH A MID LEVEL S/W CROSSING THE MID
SOUTH SATURDAY AFTERNOON-EVENING. THIS CAUSES THE GFS TO SPIN UP A
SFC WAVE ALONG THE CAD FRONT BY LATE SATURDAY OVER OUR SOUTHERN
PIEDMONT...AND LIFTING IT NWD SATURDAY NIGHT. GFS ALSO MUCH STRONGER
WITH ITS LOW LEVEL JET...DEPICTING 60-65KTS OVER THE REGION LATE
SATURDAY. ECMWF WIND PROFILE NOT AS STRONG PLUS ITS MUCH WEAKER/NOT
AS AMPLIFIED WITH THE S/W AS THE GFS. IF THE GFS SOLUTION
VERIFIES...COULD SEE POTENTIAL FOR A FEW STRONG STORMS IN THE WARM
SECTOR (EASTERN HALF OF THE CWA) LATE SATURDAY INTO SATURDAY NIGHT
AS LOW LEVEL HELICITY QUITE STRONG WITH WEAK SFC BASED INSTABILITY.

OTHERWISE...EXPECT RAIN TO OVERSPREAD CENTRAL NC SATURDAY MORNING
AND PERSIST WELL INTO SATURDAY NIGHT. THIS RAIN SHOULD LOCK IN
ANOTHER CAD AIR MASS ACROSS THE PIEDMONT...RESULTING IN BELOW NORMAL
TEMPS. UNLIKE THE LAST EVENT THOUGH...TEMPS APPEAR TOO WARM TO WORRY
ABOUT ANY WINTRY PRECIP. TEMPS SATURDAY WILL BE TRICKY ALONG THE
HIGHWAY 1 CORRIDOR AND EASTWARD AS MODELS SUGGEST THE CAD FRONT
RETREATING WESTWARD AS THE SFC WAVE DEVELOPS LATE IN THE DAY. SOME
GUIDANCE SUGGESTING LATE AFTERNOON TEMPS WELL INTO THE 60S IN OUR SE
COUNTIES...AND NEAR 60 IN THE RALEIGH AREA. STILL PLENTY OF TIME TO
MASSAGE THESE TEMPS BUT HAVE ADJUSTED TEMPS UP FROM PREVIOUS
FORECAST 3-5 DEGREES ACROSS THE EAST HALF SATURDAY AFTERNOON.

MAY SEE RAIN AMOUNTS ON THE ORDER OF ONE TO AS MUCH AS TWO INCHES
WITH THIS EVENT SATURDAY-SATURDAY NIGHT.

THE MID LEVEL S/W WILL SHEAR OUT TO THE NE SATURDAY NIGHT...DRAGGING
A SFC FRONT ACROSS CENTRAL NC SATURDAY NIGHT INTO EARLY SUNDAY.
DRIER AIR BEHIND THIS BOUNDARY WILL DIMINISH THE RAIN COVERAGE WEST-
TO-EAST SATURDAY NIGHT WITH PARTIAL CLEARING EXPECTED SUNDAY. COOL
DRY HIGH PRESSURE WILL BUILD INTO THE CAROLINAS SUNDAY AFTERNOON AND
EXTEND ACROSS THE AREA MONDAY. TEMPS WILL AVERAGE SLIGHTLY BELOW
NORMAL BOTH DAYS.
-- End Changed Discussion --

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 1 AM TUESDAY...

24-HR TAF PERIOD: ADVERSE AVIATION CONDITIONS (IFR-LIFR) ASSOCIATED
WITH A COLD AIR DAMMING WEDGE WILL PERSIST THIS MORNING THROUGH MID
TO LATE AFTERNOON TODAY AT ALL CENTRAL NC TERMINALS. CEILINGS ARE
EXPECTED TO FALL INTO THE IFR/LIFR RANGE THIS MORNING WITH LIFR TO
MVFR VISBYS. PERIODS OF RAIN WILL BE POSSIBLE THROUGH EARLY TO MID
AFTERNOON. CIGS ARE EXPECTED TO SLOWLY INCREASE INTO THE LOW END IFR
RANGE AS BY MID MORNING INTO THE AFTERNOON... CLOSE TO WHEN THE RAIN
ENDS. IN ADDITION... HAVE ADDED LLWS TO THE KFAY TAF NEAR DAYBREAK
... WHERE THE CAD AIRMASS WILL BE THE SHALLOWEST... AND MODEL
FORECAST SOUNDING ARE SHOWING WINDS NEAR DAYBREAK A COUPLE THOUSAND
FEET OFF THE SURFACE APPROACHING 40-45 KTS OUT OF THE SOUTHWEST.
LLWS CONDITIONS WILL END BY EARLY AFTERNOON AS WINDS NEAR 2K FT ARE
EXPECTED TO WEAKEN.

VFR CONDITIONS ARE EXPECTED TO RETURN TO THE AREA BY MID TO LATE
AFTERNOON WITH THE PASSAGE OF A MID LEVEL TROUGH... WHICH WILL
RESULT IN CLEARING SKIES AND PERHAPS A BRIEF PERIOD OF GUSTY
NORTHWESTERLY WINDS BEFORE SUNSET. EXPECT WE COULD SEE SOME WIND
GUSTS OF UP TO 20 MPH... MAYBE EVEN 25 MPH.

LOOKING AHEAD: VFR/DRY CONDITIONS ARE EXPECTED TO PREVAIL WED
THROUGH FRI AS HIGH PRESSURE BUILDS OVER THE REGION FROM THE WEST.
THE NEXT CHANCE FOR ADVERSE AVIATION CONDITIONS WILL BE LATE FRI
NIGHT AND SAT IN ASSOC/W A STORM SYSTEM APPROACHING THE CAROLINAS
FROM THE SOUTHWEST.
-- End Changed Discussion --

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
NONE
-- End Changed Discussion --

&&

$$

SYNOPSIS...WSS
NEAR TERM...BSD
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...BSD/VINCENT