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000
FXUS62 KRAH 110227
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
925 PM EST TUE DEC 10 2013

.SYNOPSIS...
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COLD AND DRY HIGH PRESSURE WILL BUILD OVER THE REGION
THROUGH THURSDAY. A STORM SYSTEM WILL APPROACH FROM THE SOUTHERN
PLAINS STATES LATE FRIDAY.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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AS OF 925 PM TUESDAY...

WINDS ARE CALMING AND TEMPERATURES ARE DROPPING QUICKLY AT MID
EVENING. JUST A FEW CIRRUS REMAIN... WHICH WILL BE EXITING SHORTLY.
EXPECT CLEAR SKIES OVERNIGHT. NW WINDS PERIODICALLY TO 10 MPH OR SO
WILL BECOME LIGHT. LOWS GENEARLLY IN THE 20S.
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&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 240 PM TUESDAY...

WEAK...MODIFIED HIGH PRESSURE WILL SETTLE OVER THE AREA BRIEFLY ON
WEDNESDAY...THEN GIVE WAY TO ANOTHER WEAK AND DRY COLD FRONT
WEDNESDAY NIGHT.  LOW LEVEL THICKNESSES AROUND 1300M IN THE MORNING
SUPPORT HIGHS JUST SLIGHTLY BELOW NORMAL...48-52 AND COOLEST IN THE
NORTHEAST. OUTSIDE OF SOME HIGH CLOUDS STREAM ACROSS THE SOUTHEAST
US THURSDAY NIGHT...SKIES WILL BE MOSTLY CLEAR THROUGH THE
PERIOD...EVEN AS THE AFOREMENTIONED COLD FRONT SLIPS SOUTH INTO THE
AREA OVERNIGHT.  EVEN WITH COLD ADVECTION OVERNIGHT...GUIDANCE HAS
LOW GENERALLY WITHIN A DEGREE OR TWO OF TONIGHTS LOW...AROUND 24-29
NORTHWEST TO SOUTHEAST.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
AS OF 250 PM TUESDAY...

FOR THURSDAY THROUGH 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

&&

.AVIATION /00Z WEDNESDAY THROUGH SATURDAY/...
AS OF 615 PM TUESDAY...

24 HOUR TAF PERIOD: WITH RAIN CLEARING OUT TO THE EAST EARLIER THIS
AFTERNOON ONLY A FEW CLOUDS REMAIN THIS EVENING AS HIGH PRESSURE
BEGINS TO TAKE OVER THE PATTERN FOR THE NEXT SEVERAL DAYS. WINDS
WILL BEGIN THE PERIOD OUT OF THE NORTHWEST AND STRONG GUSTING THIS
AFTERNOON...PARTICULARLY IN THE TRIAD WILL CALM DOWN OVERNIGHT WITH
WINDS GENERALLY AT 5 KNOTS OR LESS. WHILE THE ATMOSPHERE WILL
CONTINUE TO DRY OUT OVERNIGHT AND NO FOG/STRATUS IS EXPECTED
WEDNESDAY MORNING...EASTERN AREAS INCLUDING KRWI HAVE OBSERVED SOME
MVFR/IFR VISIBILITIES THAT MAY CONTINUE FOR A FEW HOURS AFTER 00Z
BUT ARE NOT EXPECTED TO CONTINUE OVERNIGHT.

ON WEDNESDAY WINDS WILL SHIFT TO SOUTHWESTERLY AS HIGH PRESSURE SETS
UP EAST OF THE AREA AND RETURN FLOW BEGINS. EXPECT DRY AND MOSTLY
CLEAR SKIES THROUGH THE REMAINDER OF THE PERIOD.

LONG TERM: MAINLY VFR CONDITIONS ARE EXPECTED FOR THE NEXT SEVERAL
DAYS. A LOW PRESSURE SYSTEM WILL APPROACH THE AREA NEAR THE END OF
THE WORK WEEK AND MAY BRING SOME ADVERSE CONDITIONS FOR THE WEEKEND.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

SYNOPSIS...PWB
NEAR TERM...PWB
SHORT TERM...SMITH
 LONG TERM...HARTFIELD
 AVIATION...ELLIS