-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 101751
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1250 PM 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 930 AM TUESDAY...

THE RESIDUAL CAD AIRMASS IS HOLDING ON THIS MORNING WHILE BEING
SLOWLY ERODED BY THE RETREATING WEDGE FRONT FROM THE SOUTH AND A
COLD FRONT CROSSING THE APPALACHIANS.  THE WEDGE FRONT AND A SOUTH-
SOUTHWESTERLY SURFACE WIND HAVE PROGRESSED INTO
SCOTLAND/CUMBERLAND/SAMPSON COUNTIES...WITH TEMPS NOW IN THE UPPER
50S AND LOWER 60S. HOWEVER...THE NORTHWARD PROGRESSION OF THE WEDGE
FRONT SHOULD SLOW AS A NARROW RAINBAND OVER THE WESTERN
PIEDMONT...AIDED BY A 50KT LOW LEVEL JET AND LOW-LEVEL FGEN...MOVES
EAST ACROSS THE CWA. WHILE NEAR TERM MODELS SHOW THE FORCING FOR
THIS BAND WEAKENING OVER THE NEXT FEW HOURS...THE SPC MESO-ANALYSIS
SHOWS UP TO 500 J/KG OF MUCAPE IMMEDIATELY AHEAD OF THE
BAND...MAINLY ALONG THE NC/SC BORDER. BECAUSE OF THIS...RAIN RATES
MAY BE LOCALLY ENHANCED TO A QUARTER INCH PER HOUR AND AN ISOLATED
LIGHTNING STRIKE CANNOT BE RULED OUT.

BY THIS AFTERNOON...DRIER AIR WILL BEGIN TO FILTER INTO THE NORTHERN
CWA AND A NORTHWESTERLY LOW-LEVEL WIND WILL DEVELOP...BRINGING
PRECIP TO AN END FROM WEST TO EAST.  THE NEAR SURFACE DRYING IN
CONJUNCTION WITH LINGERING LIGHT PRECIP MAY INITIALLY LEAD TO
EVAPORATIONALLY ENHANCED COOLING OVER THE NORTHERN PIEDMONT BEFORE
SKIES CLEAR...AND THIS SEEMS TO BE CAPTURED WELL IN THE CURRENT
GRIDDED FORECAST.  WILL ONLY MAKE MINOR ADJUSTMENTS TO TEMPS WITH
HIGHS MAXING OUT BY MIDDAY OR HOLDING STEADY IN MOST AREAS BEFORE
COOLING SETS IN THIS AFTERNOON. -SMITH

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/...
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.

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 1245 PM TUESDAY...

ONE LAST BAND OF RAIN IS MOVING THROUGH THE NC COASTAL PLAIN THIS
AFTERNOON...WITH THE BACK EDGE JUST HAVING PASSED THROUGH KRDU.  LOW
CLOUDS STILL LINGER...RANGING FROM LIFR IN THE RAIN BAND TO IFR AS
FAR WEST AS KGSO AND KINT.  A NORTHWESTERLY WIND IS BEGINNING TO
SHOW UP IN SURFACE OBS ACROSS THE WESTERN PORTIONS OF THE
STATE...AND LOW LEVEL MOISTURE WILL BEGIN TO SCOUR FROM WEST TO EAST
OVER THE NEXT FEW HOURS.  EXPECT MOST IF NOT ALL TAF SITES TO BE VFR
BY 20-22Z.  A FEW WIND GUSTS TO AROUND 20KT WILL BE POSSIBLE AS
SKIES BEGIN TO CLEAR.

ONCE THE WIND GUSTS SETTLE DOWN THIS EVENING...A WESTERLY WIND WILL
BECOME LIGHT AND VARIABLE LATE TONIGHT.  VFR CONDITIONS WILL PREVAIL.

OUTLOOK...
HIGH PRESSURE DOMINATE THE WEATHER PATTERN FOR THE LATTER
HALF OF THE WEEK.  A STORMS SYSTEM WILL IMPACT THE REGION OVER THE
WEEKEND AND WILL BRING THE NEXT CHANCE OF ADVERSE AVIATION
CONDITIONS.
-- End Changed Discussion --

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

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