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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 100059
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
759 PM EST MON DEC 9 2013

.SYNOPSIS...
-- Changed Discussion --
A COLD AIR DAMMING WEDGE WILL PERSIST OVER THE AREA
THROUGH TUESDAY AFTERNOON. DRY HIGH PRESSURE WILL BUILD INTO THE
REGION FROM THE WEST TUESDAY NIGHT AND WEDNESDAY.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 250 PM MONDAY...

CENTRAL NC REMAINS WELL ENTRENCHED WITHIN THE RESIDUAL COLD AIR
DAMMING AIRMASS TODAY...WITH THE WEDGE FRONT STILL WELL TO OUR SOUTH
NEAR THE SAVANNAH RIVER VALLEY.  WHILE THE DEPTH OF THE RESIDUAL
COLD POOL IS DECREASING...PER 12Z KGSO RAOB AND AIRCRAFT
SOUNDINGS...THERE IS STILL A 30-40KT FLOW AT 850MB AND ENOUGH WARM
ADVECTION TO KEEP STATIC STABILITY STRONG AND THE CAD LOCKED IN.
TEMPS HAVE RISEN VERY SLOWLY TODAY AND STILL RANGE FROM THE UPPER
30S TO NEAR 50.  WINDS JUST ABOVE THE SURFACE ARE FORECAST TO WEAKEN
A LITTLE THIS EVENING BEFORE A SHORTWAVE AND SURFACE LOW IMPACT THE
AREA LATER TONIGHT AND TUESDAY. AS SUCH... THE CURRENT BAND OF
PRECIP OVER THE WESTERN PIEDMONT SHOULD WEAKEN A BIT THIS
EVENING...AND IF IT DOES SO...FOG MAY REDEVELOP AFTER SUNSET.  A FEW
SITES ARE CURRENTLY REPORTING 1/2SM AND 1/4SM AROUND THE SOUTHERN
PIEDMONT...AND WE PLAN TO ISSUE AN SPS FOR THE EARLY EVENING HOURS.

TONIGHT...
A SHORTWAVE OVER THE SOUTHERN PLAINS WILL SHEAR OUT AS IT
LIFTS TOWARD THE OHIO VALLEY TONIGHT...BUT WILL RE-ENERGIZE THE
SOUTHWESTERLY FLOW LEVEL FLOW OVER THE SOUTHEAST US AND CAUSE A WEAK
AREA OF LOW PRESSURE TO DEVELOP AND ADVANCE ALONG THE SLOWLY
RETREATING WEDGE FRONT.  MEANWHILE... THE PRIMARY COLD FRONT WEST OF
THE MOUNTAINS TODAY WILL BEGIN TO CROSS THE MOUNTAINS AND BEND SOUTH
INTO THE NC FROM THE NORTH-NORTHWEST LATE TONIGHT. WHILE THE
STRONGEST FORCING FROM MID-LEVEL FGEN AND UPPER DIVERGENCE
ASSOCIATED WITH THE RIGHT ENTRANCE REGION OF THE MAIN UPPER JET WILL
PASS TO OUR NORTHWEST ACROSS THE CENTRAL APPALACHIANS...A 50KT LOW
LEVEL JET... ISENTROPIC LIFT... LOW-LEVEL FRONTOGENESIS ASSOCIATED
WITH THE COLD FRONT SHOULD BE SUFFICIENT TO PRODUCE RAIN AREAWIDE.
DETERMINISTIC MODEL QPF AMOUNTS RANGE FROM 0.25" TO 0.50" AND THE
SREF MEAN IS AROUND 0.50".  MODELS SHOW SOME WEAK INSTABILITY OVER
EASTERN NC WITH THE PASSAGE OF THE SURFACE LOW LATE TONIGHT...BUT
ITS UNCLEAR WHETHER OR NOT ISENTROPIC LIFT AND LOW-LEVEL THETA
ADVECTION WILL BE ENOUGH TO OVERCOME THE LOW-LEVEL STABILITY NORTH
OF THE WEDGE FRONT FOR ANY THUNDER.  AFTER A LULL THIS
EVENING...WILL SHOW POPS RAMPING UP TO CATEGORICAL AGAIN AFTER
MIDNIGHT AND CONTINUING INTO TUESDAY...HIGHEST IN THE WEST.  TEMPS
WILL HOLD RELATIVELY STEADY IN THE UPPER 30S AND 40S
TONIGHT...POSSIBLY RISING SLIGHTLY IN THE SOUTH WITH THE APPROACH OF
THE SURFACE LOW.

TUESDAY... THE PASSAGE OF THE AFOREMENTIONED SHORTWAVE TO OUR NORTH
WILL SWEEP THE SURFACE COLD FRONT ACROSS THE AREA...WITH PRECIP
COMING TO AN END BETWEEN 18Z AND 00Z WITH THE ARRIVAL A DRIER AND
GUSTY NORTHWESTERLY WIND.  THICKNESSES BEGIN TO CRASH AFTER
18Z...BUT FORECAST SOUNDINGS ARE DRY ABOVE 0C AND PRECIP SHOULD END
AS JUST RAIN.  HIGHS 43 TO 60 NORTHWEST TO SOUTHEAST.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 250 PM MONDAY...

FOR TUESDAY NIGHT: BOTH THE MID LEVEL TROUGH AXIS AND THE RIGHT REAR
QUAD OF THE UPPER JET WILL BE MOVING QUICKLY OFF THE NORTHEAST COAST
EARLY TUE EVENING... AS THE SURFACE FRONT PUSHES OFFSHORE. SURFACE
HIGH PRESSURE NOW CENTERED JUST EAST OF THE CENTRAL ROCKIES WILL
BEGIN TO BUILD IN FROM THE WEST... WITH THICKNESSES CONTINUING TO
DROP... DOWN INTO THE 1290S BY DAYBREAK. DRY AIR PUNCHING IN ALOFT
ON FLAT WESTERLY MID LEVEL FLOW ALONG WITH DIFFLUENT AND DOWNSLOPE
WNW FLOW 850 MB SHOULD YIELD RAPID CLEARING WITH A VERY STABLE AND
DRY COLUMN. THE COMBINATION OF COLD AIR ADVECTION... TYPICAL
NOCTURNAL COOLING FACILITATED BY CLEAR SKIES...AND DIMINISHING
SURFACE WINDS WILL MAKE FOR A CHILLY OVERNIGHT. PREFER LOWS ON THE
LOW END OF STATISTICAL GUIDANCE... 24-31.

FOR WEDNESDAY THROUGH THURSDAY NIGHT: COOL AND FAIRLY QUIET. THE
SURFACE HIGH WEAKENS A BIT AS IT DRIFTS OVERHEAD WED... THEN A
SECONDARY MID LEVEL TROUGH AND REINFORCING SURFACE COLD FRONT
APPROACH FROM THE WNW AND MOVE QUICKLY THROUGH CENTRAL NC BETWEEN
03Z AND 09Z WED NIGHT. THE COLUMN WILL REMAIN DRY AND FAIRLY
STABLE... SO EXPECT NO PRECIP WITH THIS FRONTAL PASSAGE... ALTHOUGH
THE VERTICAL WIND AND THERMAL STRUCTURE COMBINED WITH A POCKET OF
SOMEWHAT MOIST AIR AROUND 500 MB MAY LEAD TO DEVELOPMENT OF
OROGRAPHICALLY ENHANCED HIGH CLOUDS OVERNIGHT INTO EARLY THU
MORNING. OTHERWISE... EXPECT GENERALLY CLEAR SKIES AND BELOW-NORMAL
TEMPS. LOW LEVEL THICKNESSES START OUT ROUGHLY 25 M BELOW NORMAL
WED... THEN IN THE WAKE OF THE REINFORCING FRONT WED NIGHT...
THICKNESSES DROP FURTHER TO AROUND 35-40 M BELOW NORMAL. EXPECT
HIGHS 45-50 WED AND 39-46 THU. LOWS 24-31 WED NIGHT AND LOW-MID 20S
THU NIGHT AS AN ARCTIC-SOURCE HIGH BUILDS OVERHEAD. -GIH

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
-- Changed Discussion --
AS OF 320 PM MONDAY...

FAIRLY QUIET FRI AND MON... WITH A GOOD CHANCE OF RAIN OVER THE
WEEKEND. THE SURFACE HIGH SHIFTS OFF THE COAST FRIDAY... AND THE
SUBSEQUENT RETURN FLOW ALLOWS THE OLD FRONTAL ZONE OVER THE FAR NRN
GULF TO SURGE NORTHWARD BACK TOWARD NC FRI NIGHT... PROPELLED BY
STRENGTHENING SOUTHERLY 850 MB WINDS. MID LEVEL TROUGHING WITHIN THE
SPLIT FLOW EJECTS OUT OF THE DESERT SOUTHWEST LATE FRI... TRACKING
EASTWARD WHILE RELOADING WITH NRN STREAM ENERGY DROPPING OUT OF THE
PACIFIC NORTHWEST. THE APPROACH OF THIS TROUGH ALOFT WILL MAKE FOR
INCREASING AND THICKENING HIGH CLOUDS FRI NIGHT... WHILE THE
PRE-FRONTAL LOW LEVEL WARM MOIST CONVEYOR BELT WILL LEAD TO RAPIDLY
INCREASING LOW CLOUDS... WITH POTENTIAL DRIZZLE LATE FRI NIGHT. THIS
SURGE IN LOW LEVEL MOISTURE WILL OVERRIDE THE RETREATING SURFACE
RIDGE AND LIKELY RESULT IN DAMMING WEDGE OVER THE NRN AND WRN
PIEDMONT... A SOLUTION AGREED UPON BY THE GFS/ECMWF. WILL BRING IN
LOW CHANCE POPS (HIGHER SW) OF DRIZZLE OR LIGHT RAIN LATE FRI NIGHT.
GIVEN THE GOOD MODEL AGREEMENT AND CONSISTENCY WITH A STRONG INFLUX
OF MOISTURE RIGHT OUT OF THE GULF AHEAD OF THE FRONT... EXPECT A
GOOD TO LIKELY PROBABILITY OF RAIN SAT/SAT NIGHT... WITH A FEW
STORMS POSSIBLE AS FORECAST SOUNDINGS SHOW A FEW HUNDRED J/KG OF
MOSTLY ELEVATED CAPE. THE GFS IN FACT DEPICTS A TRIPLE POINT LOW AND
A BIT BETTER INSTABILITY... SO WILL NEED TO KEEP AN EYE OUT FOR
POSSIBLE STRONG STORMS LATE SAT. LOOKS LIKE THE FRONT WILL CLEAR OUT
TO OUR EAST SUN MORNING WITH RAPID IMPROVEMENT. SHOULD SEE A GOOD
BIT OF SUNSHINE BY SUN AFTERNOON... THEN AS THE MID LEVEL TROUGH
SHIFTS THROUGH SUN NIGHT... GREATER COLD AIR ADVECTION SHOULD FOLLOW
FOR MONDAY. GFS IS ALMOST 50 M COLDER THAN THE ECMWF MON MORNING...
AND WITH THIS DISCREPANCY AND THE LACK OF A CLEAR WINNER... WILL BE
CONSERVATIVE WILL THE COOLING AND INDICATE HIGHS IN THE MID 40S TO
LOW 50S SUN... AND THE LOW-MID 40S MON. -GIH
-- End Changed Discussion --

&&

.AVIATION /00Z TUESDAY THROUGH FRIDAY/...
-- Changed Discussion --
AS OF 745 PM MONDAY...

24-HR TAF PERIOD: ADVERSE AVIATION CONDITIONS (IFR-VLIFR) ASSOCIATED
WITH A COLD AIR DAMMING WEDGE WILL PERSIST TONIGHT AND MOST OF THE
DAY TUESDAY AT ALL TERMINALS. EXPECT CEILINGS TO FALL BELOW 500 FT
AGL EVERYWHERE OVERNIGHT...ALONG WITH A POTENTIAL FOR DENSE FOG.
PERIODIC RAIN CAN BE EXPECTED AT THE RDU TERMINAL THROUGH AT LEAST
06Z. PREVIOUS FORECASTS MENTIONED LLWS OVERNIGHT AND THE PRESENCE OF
A STRONG COLD AIR DAMMING WEDGE CERTAINLY INDICATES A
CLIMATOLOGICALLY FAVORABLE ENVIRONMENT FOR LLWS TO OCCUR. THE LATEST
MODEL GUIDANCE SUGGESTS INCREASED UNCERTAINTY W/REGARD TO WHETHER OR
NOT NON-CONVECTIVE LLWS CRITERIA WILL BE MET TONIGHT/TUE MORNING. AS
A RESULT...HAVE OPTED TO OMIT ANY EXPLICIT MENTION OF LLWS WITH THE
00Z TAF ISSUANCE. CONDITIONS WILL IMPROVE LITTLE TUESDAY MORNING...
WITH AN INCREASING POTENTIAL FOR RAIN BY OR SHORTLY AFTER SUNRISE AT
ALL TERMINALS AS A COLD FRONT APPROACHES FROM THE WEST. CONDITIONS
WILL BEGIN TO IMPROVE TO MVFR AND PERHAPS VFR FROM WEST-EAST BY THE
END OF THE TAF PERIOD (00Z WED) AS A DRIER AIRMASS MOVES INTO THE
REGION BEHIND THE FRONT.

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. -VINCENT
-- End Changed Discussion --

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

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