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000
FXUS62 KRAH 130830
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
330 AM EST FRI DEC 13 2013

.SYNOPSIS...HIGH PRESSURE WILL EXTEND ACROSS THE REGION THIS MORNING
THEN DRIFT OFFSHORE THIS AFTERNOON. A LOW PRESSURE SYSTEM WILL
DEVELOP OVER THE DEEP SOUTH TONIGHT... THEN TRACK NORTHEAST OVER THE
CAROLINAS AND MID ATLANTIC REGION THIS WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM FRIDAY...

TODAY...SURFACE HIGH OVER TEH AREA EARLY THIS MORNING WILL SCOOT
EASTWARD AND LIE OFFSHORE LATER TODAY. RETURN SW FLOW WILL FUNNEL
WARMER AIR INTO THE REGION. THIS REFLECTED IN LOW LEVEL THICKNESSES
RECOVERING INTO THE 1312-16M RANGE...ABOUT 20M HIGHER THAN THURSDAY
BUT STILL 15M BELOW NORMAL FOR MID DECEMBER. EXPECT TEMPS TO REBOUND
QUICKLY FROM EARLY MORNING TEMPS IN THE LOW-MID 20S...REACHING THE
MID-UPPER 40S BY NOON ..AND 50-55 FOR AFTERNOON MAX TEMPS. EXPECT TO
SEE AN INCREASE IN HIGH LEVEL CLOUDS THIS AFTERNOON BUT APPEARS THAT
THESE HIGH CLOUDS WILL NOT THICKEN IN TIME TO HAVE AN EFFECT ON MAX
TEMPS.

TONIGHT...HIGH CLOUDS WILL CONTINUE TO THICKEN AS A S/W IN THE
SOUTHERN STREAM MOVES EAST ACROSS THE SOUTHERN PLAINS-LOWER MS
VALLEY. MODEL GUIDANCE IN GOOD AGREEMENT IN DELAYING ARRIVAL OF
PRECIP UNTIL CLOSE TO DAYBREAK SO HAVE DELAYED ARRIVAL OF SLIGHT
CHANCE POPS A FEW HOURS FROM PREVIOUS FORECAST. THIS DELAYED ARRIVAL
ALSO SUGGEST THAT THE THREAT FOR FREEZING RAIN/FREEZING DRIZZLE ON
ITS ONSET IN THE WESTERN PIEDMONT ARE NOT AS MUCH AS A CONCERN AS
EARLIER IN THE WEEK BUT STILL NEEDS TO BE MONITORED A SFC WET BULB
TEMPS HOVER NEAR FREEZING ACROSS THE NW PIEDMONT UNTIL SHORTLY AFTER
DAYBREAK. MIN TEMPS GENERALLY IN THE MID 30S...AND LIKELY REALIZED
AROUND MIDNIGHT AS THICKENING CLOUD COVER OVERNIGHT SHOULD AID TO
STABILIZE TEMPS.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
AS OF 330 AM FRIDAY...

SATURDAY...MODEL GUIDANCE HAS COME INTO GOOD AGREEMENT CONCERNING
THE ONSET OF A COLD AIR DAMMING EVENT ACROSS CENTRAL NC AND THE
MOVEMENT/TIMING OF A SFC WAVE AND ATTENDANT SFC BOUNDARY CROSSING
THE REGION AND ENDING THE CAD EVENT SATURDAY NIGHT.

INITIAL S/WE OVER THE LOWER MC VALLEY EARLY SATURDAY QUICKLY SHEARS
OUT TO THE NE IN RESPONSE TO ANOTHER BUT STRONGER S/W FOLLOWING
CLOSELY ON ITS HEELS...CROSSING THE SOUTHERN PLAINS SATURDAY. THESE
TANDEM OF S/WS WILL ENHANCE THE LOW LEVEL SLY FLOW AND ASSOCIATED
MOISTURE TRANSPORT FROM THE NORTHERN GULF INTO THE CAROLINAS
SATURDAY. THIS INFLUX OF MOISTURE COUPLED WITH INCREASING UPGLIDE IN
THE LOWER LEVELS AND INCREASING DIVERGENCE ALOFT ASSOCIATED WITH THE
NOSE A STRONG 300MB JET CROSSING THE DEEP SOUTH WILL CAUSE RAIN TO
BLOSSOM ACROSS CENTRAL NC BY LATE SATURDAY MORNING AND CONTINUE INTO
SATURDAY AFTERNOON. THIS RAIN FALLING THROUGH THE DRY STABLE AIR
MASS DEPOSITED BY THE SFC HIGH CURRENTLY OVERHEAD WILL INITIATE AND
LOCK IN AN INSITU DAMMING EVENT. THE WEDGE BOUNDARY THAT DEVELOPS
SHOULD LIE IMMEDIATELY TO OUR SE SATURDAY MORNING THEN DRIFT SLOWLY
NW INTO TEH SANDHILLS/COASTAL PLAIN BY LATE IN THE DAY. THIS
BOUNDARY SHOULD CAUSE A DECENT TEMP VARIATION ACROSS CENTRAL NC WITH
LATE AFTERNOON TEMPS IN THE UPPER 30S/AROUND 40 IN THE NW TO THE
UPPER 50S/AROUND 60 IN THE FAR E-SE. EXPECT THE HEAVIEST RAINFALL TO
FALL ON THE COOL SIDE OF THE WEDGE BOUNDARY WHICH WOULD FAVOR THE
SOUTHERN-EASTERN PIEDMONT INTO THE NORTHERN COASTAL PLAIN. SINCE
BEST LIFT OVER THE REGION BETWEEN 16Z-00Z...AND NOT OVER A SPAN OF
12-18Z HOURS AS ADVERTISED 2-3 DAYS AGO...RAINFALL TOTALS ON THE
ORDER OF A HALF TO ONE INCH EXPECTED WITH ISOLATED AMOUNTS AROUND
1.25 INCHES POSSIBLE.

WHILE FAVORABLE KINEMATICS IN PLACE FOR CONVECTION...AVAILABLE
INSTABILITY TO INITIATE/SUSTAIN CONVECTION VIRTUALLY NON-EXISTENT.
THUS CHANCES FOR CONVECTION TOO MINUSCULE TO MENTION IN THE FORECAST
AT THIS TIME.

NOW APPEARS THAT THE 850MB TROUGH WILL SLIDE EAST ACROSS THE REGION
EARLY SATURDAY EVENING...VEERING WINDS IN TEH 925-850MB LEVEL TO A
MORE WLY FLOW. THIS FLOW WILL AID TO SHUT DOWN PRECIP GENERATION
FROM WEST-TO-EAST DURING THE EVENING HOURS. IF MODEL TIMING
VERIFIES...PRECIP MAY END SHORTLY AFTER 7 PM IN THE WEST...PRIOR TO
MIDNIGHT IN THE EAST. FAVOR A SLOWER TIMING...SIMILAR TO THE ECMWF
WHICH TAPERS PRECIP FROM WEST-TO-EAST LATE EVENING INTO THE
OVERNIGHT HOURS. MIN TEMPS EXPECTED TO RANGE FROM THE UPPER 30S NW
TO THE MID-UPPER 40S SE.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 305 AM FRIDAY...

SUNDAY AND SUNDAY NIGHT: STRENGTHENING SURFACE LOW PRESSURE WILL
LIFT OFF TO THE NORTHEAST ON SUNDAY AS MID LEVEL DRY AIR SURGES INTO
THE REGION. THIS WILL LEAD TO A DRYING CONDITIONS... WITH MOSTLY TO
PARTLY SUNNY SKIES AT LEAST RETURNING BY SUNDAY AFTERNOON. THUS...
WITH IMPROVING CONDITIONS ON SUNDAY AND DOWNSLOPE FLOW WILL RAISE
HIGH TEMPS BY A COUPLE OF DEGREES AND END ALL POPS BY MID MORNING AT
THE LATEST. THIS YIELDS HIGH TEMPS RANGING FROM AROUND 50 NW TO MID
50S SOUTH AND EAST. SOME STATISTICAL GUIDANCE ALONG WITH THE IN
HOUSE LOW LEVEL THICKNESS SCHEME IS SHOWING HIGH TEMPS APPROACHING
THE UPPER 50S TO AROUND 60 FOR SUNDAY ACROSS THE SOUTHEAST.
HOWEVER... MODEL SOUNDINGS ARE SHOWING A RATHER SHALLOW MIXED LAYER
ACROSS OUR SOUTHEAST/SOUTH... ALONG WITH POSSIBLY SOME LINGERIN LOW
LEVEL MOISTURE. THUS... WILL LIMIT/CAP HIGHS FOR SUNDAY IN THE MID
50S.

SURFACE HIGH PRESSURE WILL BE BUILDING INTO THE AREA FROM THE GULF
COAST STATES ON SUNDAY NIGHT. THUS... WILL RAISE LOWS TEMPS FROM THE
PREVIOUS FORECAST A BIT... SHOWING LOWS AROUND FREEZING WITH CLEAR
SKIES.

MONDAY THROUGH THURSDAY: QUITE WEATHER IS EXPECTED FOR THE MEDIUM
RANGE PORTION OF THE FORECAST... WITH GENERALLY A WEAK L/W TROUGH
ACROSS THE EASTERN HALF OF THE COUNTRY. ANY S/W ENERGY WILL REMAIN
IN THE NORTHERN STREAM AND ONLY SEND A WEAK DRY COLD FRONT ACROSS
CENTRAL NC IN THE TUESDAY INTO TUESDAY NIGHT TIME FRAME. GIVEN THE
LACK OF MOISTURE WITH THIS SYSTEM WILL KEEP THE FORECAST DRY AND
ONLY SHOW A VERY MINOR INCREASE IN CLOUD COVER (MAINLY MID AND HIGH
CLOUDS). MODELS DIFFER THOUGH WITH HOW THEY HANDEL THE EVOLUTION OF
THE NEXT SIGNIFICANT SYSTEM EXPECTED TO MOVE INTO THE CENTRAL PART
OF THE COUNTRY BY THE END OF NEXT WEEK. WHILE WE DO NOT EXPECT ANY
PRECIP ON THURSDAY AT THIS TIME... THE GFS AND ECMWF DIFFER WRT THE
LOW LEVEL PATTERN. THE GFS IS MORE AGGRESSIVE IN BUILDING A 1038 MB
HIGH INTO THE AREA FROM THE NORTH... WHILE THE ECMWF DEPICTS A
WARMING SOUTHERLY RETURN FLOW FOR THE AREA... WITH THE MAIN FRONTAL
ZONE TO THE NORTH OF CENTRAL NC. FOR NOW WILL STICK CLOSE TO WPC AND
KEEP THE WARMER SOLUTION FOR US (ALTHOUGH NOT NEAR AS WARM AS THE
ECMWF IS DEPICTING AT THIS TIME)... WHICH IS IN AGREEMENT WITH THE
LATEST ECMWF. TEMPS DURING THE MEDIUM RANGE WILL START OFF SLIGHTLY
BELOW NORMAL AND TREND TO NEAR TO SLIGHTLY ABOVE NORMAL BY MID TO
LATE IN THE PERIOD (WITH THE POSSIBILITY OF WELL ABOVE NORMAL NEAR
THE END OF THE PERIOD IF THE LATEST ECMWF VERIFIES).

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
AS OF 1245 AM FRIDAY...

AN AREA OF HIGH PRESSURE OVER THE SE U.S. WILL CAUSE VFR CONDITIONS
ACROSS CENTRAL NC THROUGH THIS EVENING. LIGHT AND VARIABLE SURFACE
WINDS EARLY TODAY WILL BECOME SW BETWEEN 5-7KTS THIS AFTERNOON. A
VEIL OF HIGH CLOUDS WILL INCREASE AND THICKEN LATE TODAY AND THIS
EVENING.

VFR CONDITIONS TONIGHT WILL QUICKLY DETERIORATE SATURDAY MORNING
AFTER DAYBREAK AS AN AREA OF LOW PRESSURE OVER THE DEEP SOUTH
FUNNELS MOISTURE INTO THE CAROLINAS. THERE IS A HIGH LIKELIHOOD OF
IFR/LOW END MVFR CEILINGS DEVELOPING ACROSS CENTRAL NC PRIOR TO NOON
SATURDAY AND PERSISTING INTO SATURDAY NIGHT. RAIN WILL BECOME
WIDESPREAD AS WELL WITH MVFR/IFR VISIBILITIES DUE TO RAIN AND FOG
HIGHLY PROBABLE SATURDAY AFTERNOON INTO SATURDAY EVENING.

THE AREA OF LOW PRESSURE WILL CROSS AND LIFT NE ACROSS THE CAROLINAS
SATURDAY NIGHT. NW FLOW ON THE BACKSIDE OF THE DEPARTING LOW WILL
ADVECT DRIER AIR INTO CENTRAL NC...LEADING TO IMPROVING AVIATION
CONDITIONS SUNDAY MORNING. SFC WINDS WILL BECOME BLUSTERY WITH
SUSTAINED 10-15KTS AND GUSTS AROUND 25KTS FROM LATE SUNDAY MORNING
THROUGH THE AFTERNOON.

VFR CONDITIONS APPEAR LIKELY FOR MONDAY INTO TUESDAY AS HIGH
PRESSURE CENTERED OVER THE DEEP SOUTH WILL BE THE DOMINATE WEATHER
FEATURE FOR OUR REGION.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

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