-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 110746
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
246 AM EST WED DEC 11 2013

.SYNOPSIS...COOL AND DRY HIGH PRESSURE WILL BUILD INTO THE REGION
THIS MORNING AND MOVE ACROSS THE AREA THIS AFTERNOON. A DRY COLD
FRONT WILL MOVE ACROSS THE REGION TONIGHT... WITH COLD HIGH PRESSURE
BUILDING INTO THE AREA ON THURSDAY BEHIND THE FRONT.

 &&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 215 AM WEDNESDAY...

TODAY: SURFACE HIGH PRESSURE WILL MOVE ACROSS THE AREA TODAY... WITH
A DRY WESTERLY FLOW ALOFT. THIS WILL YIELD SUNNY/MOSTLY SUNNY SKIES
TODAY WITH GENERALLY LIGHT WINDS AND SLIGHTLY BELOW NORMAL TEMPS.
AFTERNOON LOW LEVEL THICKNESS VALUES ARE EXPECTED TO BE IN THE 1315
TO 1325 METER RANGE ACROSS THE AREA. KEEPING IN MIND THAT THE
EASTERN/NORTHERN EASTERN PART OF THE CWA WILL NOT SEE ANY LOW LEVEL
RETURN FLOW UNTIL LATE IN THE DAY... WILL GO WITH HIGH TEMPS RANGING
FROM THE LOWER TO MID 50S SW TO UPPER 40S NE.

TONIGHT: A QUICK MOVING DRY COLD FRONT WILL SWEEP ACROSS THE REGION
TONIGHT. OUTSIDE OF A BRIEF INCREASE IN MID TO HIGH CLOUDS
ACCOMPANYING THE SYSTEM... EXPECT MOSTLY CLEAR SKIES TONIGHT WITH
LIGHT SOUTHWESTERLY WINDS TO START THE NIGHT BECOMING NORTHWESTERLY
BEHIND THE FRONT AN INCREASING TO AROUND 5 TO 10 MPH. THE
NORTHWESTERLY BREEZE OVERNIGHT MAY ACTUALLY HELP TO KEEP TEMPS UP A
BIT. THUS.. WILL GO WITH LOWS RANGING FROM THE MID TO UPPER 20S
ACROSS THE AREA.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
AS OF 240 AM WEDNESDAY...

THURSDAY AND THURSDAY NIGHT: SURFACE HIGH PRESSURE WILL BUILD INTO
THE AREA ON THURSDAY AND SETTLE ACROSS THE REGION ON THURSDAY NIGHT.
THIS HIGH HAS MORE OF AN ARCTIC ORIGIN AND THUS WILL RESULT IN COLD
TEMPS FOR THURSDAY AND THURSDAY NIGHT. ANY MOISTURE ALOFT WILL
REMAIN TO THE WEST OF AN NORTH OF CENTRAL NC DURING THIS TIME.
THUS... EXPECT MOSTLY SUNNY/CLEAR CONDITIONS... WITH A NORTH-
NORTHWESTERLY BREEZE ON THURSDAY (8-12 MPH)... BEFORE WINDS SUBSIDE
WITH SUNSET/LOSS OF MIXING ALONG WITH A WEAKENING PRESSURE GRADIENT.
AFTERNOON LOW LEVEL THICKNESS VALUES ARE PROGGED TO BE AROUND 20 TO
25 METERS LOWER THAN THIS AFTERNOON. THUS... EXPECT CHILLY WELL
BELOW NORMAL HIGHS ON THURSDAY DESPITE FULL SUN. WILL GO WITH HIGH
TEMPS RANGING FROM THE LOWER 40/AROUND 40 NORTH TO THE MID 40S
SOUTH. LOWS FRIDAY MORNING WILL BE COLD... GIVEN THE SURFACE HIGH IS
EXPECTED TO BE OVER THE AREA DURING THIS TIME ALONG WITH CLEAR SKIES
AND DEWPOINT TEMPS AT BEST IN THE TEENS. THUS... EXPECT LOW TEMPS TO
RANGE FROM AROUND 20 TO MAYBE EVEN A FEW TEENS IN THE USUAL RURAL
COLD SITES TO THE MID 20S IN SOME OF THE URBAN AREAS AND FAR
SOUTHEAST.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 250 PM TUESDAY...

FRIDAY: COOL AND QUIET. THE SECONDARY MID LEVEL TROUGH AND
REINFORCING SURFACE COLD FRONT WILL MOVE RAPIDLY ESE THROUGH CENTRAL
NC DURING THE EARLY MORNING HOURS THU. 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 EARLY THU
MORNING. OTHERWISE... EXPECT GENERALLY CLEAR SKIES AND MUCH BELOW-
NORMAL TEMPS THU AND THU NIGHT. LOW LEVEL THICKNESSES DROP TO AROUND
35-40 M BELOW NORMAL... SUPPORTING CHILLY HIGHS OF 39-46 THU. EXPECT
COLD LOWS OF 20-26 THU NIGHT (WITH SOME UPPER TEENS IN OUTLYING
AREAS) AS AN ARCTIC-SOURCE HIGH BUILDS OVERHEAD WITH CLEAR SKIES AND
CALM WINDS. THE SURFACE HIGH SHIFTS OFF THE COAST FRI... AS A MID
LEVEL SHORTWAVE TROUGH WITHIN THE SPLIT FLOW EJECTS OUT OF THE
DESERT SOUTHWEST... TRACKING EASTWARD WHILE RELOADING WITH NRN
STREAM ENERGY DROPPING OUT OF THE PACIFIC NORTHWEST. THE APPROACH OF
THIS TROUGH IS LIKELY TO BRING INCREASING HIGH THIN CLOUDS FROM THE
WEST DURING FRI AFTERNOON. LOW-MID LEVEL FLOW WILL SWING AROUND TO
BE UNIFORMLY FROM THE SW... BUT WITH SHALLOW MIXING AND THE SURFACE
RIDGE STILL EXTENDING BACK ACROSS NC... MUCH OF THIS WARMING WILL
TAKE PLACE ABOVE 925 MB... LEAVING JUST MODEST WARMING AT THE
SURFACE. HIGHS FRI 45-51... AROUND 5-8 DEGREES BELOW NORMAL.

FOR FRIDAY NIGHT THROUGH SUNDAY: A STORMY WEEKEND AHEAD. AS THE
TROUGH ALOFT APPROACHES... THICKENING HIGH CLOUDS WILL CONTINUE TO
OVERSPREAD NC FRI NIGHT WITH LOWERING CLOUD BASES. AT THE SAME
TIME... THE PREFRONTAL LOW LEVEL WARM MOIST CONVEYOR BELT WILL LEAD
TO RAPIDLY INCREASING LOW CLOUDS FRI NIGHT... WITH THE POTENTIAL FOR
AREAS OF DRIZZLE LATE AS THE GFS/ECMWF INDICATE QUICKLY
STRENGTHENING MOIST UPGLIDE AT 290K-295K. THIS SURGE IN LOW LEVEL
MOISTURE WILL OVERRIDE THE RETREATING SURFACE RIDGE AND ITS INITIAL
LOW DEW POINTS (IN THE SINGLE DIGITS (IN THE 20S FRI EVENING) AND IS
LIKELY TO RESULT IN AN IN SITU DAMMING WEDGE OVER THE NRN AND WRN
PIEDMONT HEADING INTO SAT... A SOLUTION AGREED UPON BY THE
GFS/ECMWF. ITS DIFFICULT TO PREDICT AT THIS TIME RANGE EXACTLY WHERE
THE WEDGE FRONT WILL SET UP ON SAT... WITH THE GFS PLACING IT
THROUGH THE MIDDLE OF CENTRAL NC (BISECTING THE TRIANGLE AREA) WHILE
THE ECMWF IS FURTHER SE OVER THE COASTAL PLAIN (MORE SE THAN ITS
PREVIOUS RUNS). THE TEMP SPREAD EITHER SIDE OF THIS LINE COULD
EASILY BE 20 DEGREES OVER A SHORT DISTANCE ORTHOGONAL TO THE WEDGE
FRONT... ENSURING LOW CONFIDENCE IN THE SAT TEMP FORECAST.
CONFIDENCE IS MUCH HIGHER IN THE PRECIP FORECAST... GIVEN THE
MODELS` INDICATION OF A STRONG LOW LEVEL CONFLUENT MOISTURE FEED OUT
OF THE GULF AND A SURGE OF HIGH PW OF NEARLY 300% OF NORMAL SAT
AHEAD OF THE TROUGH AS IT CROSSES THE MS VALLEY. WILL BRING IN A LOW
CHANCE (MAINLY IN THE W) OF DRIZZLE OR LIGHT RAIN LATE FRI NIGHT...
THEN RAMP UP TO LIKELY TO CATEGORICAL POPS SAT THROUGH SAT NIGHT. A
FEW LOW-TOPPED ROTATING STORMS REMAIN POSSIBLE SAT AFTERNOON AND
EVENING... AS FORECAST SOUNDINGS SHOW A FEW HUNDRED J/KG OF MOSTLY
ELEVATED CAPE... AND BOTH THE GFS AND ECMWF DEPICT A TRIPLE POINT
LOW TRACKING NE ALONG THE WEDGE FRONT WITH STRONG LOW LEVEL SHEAR IN
THE VICINITY OF THE FRONT AND ESPECIALLY NEAR THE LOW. RIGHT NOW IT
LOOKS LIKE THE BEST CHANCE OF A STRONG ROTATING CELL WILL BE 21Z-
06Z... WHEN THE GREATEST LOW LEVEL HELICITY (OVER 400 M2/S2 AT 0-2
KM) COINCIDES WITH THE BEST (BUT STILL MEAGER) INSTABILITY (MUCAPE
OF 100-200 J/KG AT MOST). MODELS SHOW THE TRIPLE POINT LOW TRACKING
QUICKLY TO OUR NE OVERNIGHT (06Z-09Z) SAT NIGHT WITH THE WEDGE FRONT
SHIFTING TO OUR EAST BY 12Z... IN TANDEM WITH DRYING ALOFT AND
EVENTUAL LOW LEVEL DOWNSLOPE FLOW SUN MORNING. WE SHOULD SEE A GOOD
BIT OF SUNSHINE BY SUN AFTERNOON... WITH TEMPS ACTUALLY HOLDING
FAIRLY CLOSE TO NORMAL AS THICKNESSES ARE CLOSE TO NORMAL.

FOR SUN NIGHT THROUGH TUE: AS THE MID LEVEL TROUGH SHIFTS THROUGH
SUN NIGHT THROUGH MON MORNING... GREATER COLD AIR ADVECTION SHOULD
FOLLOW... WITH TEMPS DROPPING BACK WELL BELOW NORMAL FOR MONDAY. THE
GFS REMAINS COLDER THAN THE ECMWF MON (BY ABOUT 15 M)... A MUCH
SMALLER GAP THAN YESTERDAY`S RUNS. THE AVERAGE OF THESE THICKNESSES
IS STILL AT LEAST 30-35 M BELOW NORMAL AS ANOTHER CHILLY ARCTIC HIGH
BUILDS IN FROM THE NW... SO WILL INDICATE HIGHS IN THE LOW-MID 40S
MON. COLD TUE NIGHT WITH A DRY STABLE COLUMN AND THE SURFACE RIDGE
OVERHEAD... LOWS IN THE MID 20S. CONTINUED FAIR ON TUE WITH THE (BY-
NOW MODIFYING) SURFACE RIDGE STILL SPANNING NC... A DRY COLUMN...
AND FAST AND GENTLY CYCLONIC MID LEVEL FLOW. HIGHS STILL A BIT BELOW
NORMAL. -GIH
-- End Changed Discussion --

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AS OF 1220 AM WEDNESDAY...

24 HOUR TAF PERIOD: HIGH CONFIDENCE OF VFR CONDITIONS
CONTINUING THROUGH THE 24 HOUR TAF PERIOD.

HIGH PRESSURE WILL MOVE ACROSS THE AREA TODAY... RESULTING IN
GENERALLY LIGHT AN VARIABLE WINDS AND MOSTLY CLEAR SKIES. WE MAY SEE
SOME WINDS APPROACH 10 MPH OUT OF THE SOUTHWEST AT KGSO/KINT AS THE
HIGH SHIFTS EASTWARD DURING THE AFTERNOON... BEFORE WINDS DECREASE
WITH SUNSET. A DRY COLD FRONT WILL QUICKLY MOVE ACROSS THE AREA
TONIGHT/THURSDAY MORNING... RESULTING IN CONTINUED VFR CONDITIONS.

LONG TERM: VFR CONDITIONS ARE EXPECTED THROUGH FRIDAY. A LOW
PRESSURE SYSTEM WILL APPROACH THE AREA NEAR THE END OF THE WORK WEEK
AND WILL LIKELY BRING ADVERSE AVIATION CONDITIONS FOR THE WEEKEND.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

SYNOPSIS...BSD
NEAR TERM...BSD
SHORT TERM...BSD
LONG TERM...HARTFIELD
AVIATION...BSD