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000
FXUS62 KRAH 060307
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1005 PM EST WED MAR 5 2014

.SYNOPSIS...
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CANADIAN HIGH PRESSURE WILL BUILD SOUTH INTO THE
CAROLINAS OVERNIGHT. A LOW PRESSURE SYSTEM WILL STRENGTHEN ALONG
THE GULF COAST ON THURSDAY...THEN TRACK NORTHEAST ALONG OR
OFFSHORE THE SOUTHEAST COAST ON FRIDAY.
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&&

.NEAR TERM /THROUGH THURSDAY/...
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AS OF 1005 PM WEDNESDAY...

MAIN ADJUSTMENT TO THE NEAR TERM FORECAST WAS TO LOWER MIN TEMPS 2-3
DEGREES AND MAINTAIN MOSTLY CLEAR SKIES UNTIL 2-3 AM.

SUBSIDENCE IN THE WAKE OF THE EXITING MID LEVEL TROUGH HAS AIDED TO
TEMPORARILY CLEAR SKIES ACROSS CENTRAL NC THIS EVENING. AT THE SAME
TIME...A DRY AIR SURFACE RIDGE WAS BUILDING SWD INTO THE CAROLINAS
FROM A PARENT HIGH (1040MB) POSITIONED OVER WESTERN QUEBEC. THE
INFLUENCE OF THIS DRY AIR RIDGE NOTED BY AN AXIS OF LOWER DEWPOINTS
WHICH COVERED THE NORTHERN PIEDMONT AS DEWPOINTS WERE IN THE TEENS
TO AROUND 20. ELSEWHERE DEWPOINTS IN THE 20S TO NEAR 30 WERE COMMON.
THIS DRY AIR RIDGE IS PROJECTED TO BECOME MORE FIRMLY ENTRENCHED
ACROSS CENTRAL NC OVERNIGHT. THIS DRIER AIR MASS COUPLED WITH DECENT
LOW LEVEL CAA (+4 AT 850MB AT GSO VERSUS -7 AT IAD) AND CLEAR SKIES
THROUGH 2-3 AM SHOULD ALLOW TEMPS TO TUMBLE INTO THE 20S ACROSS THE
MAJORITY OF CENTRAL NC WITH MID 20S COMMON OVER THE NORTHERN HALF
AND THE COLDER LOCATIONS IN THE SOUTHERN PIEDMONT. TEMPS MAY
STABILIZE AFTER 3 AM AS CLOUDS BEGIN TO INCREASE FROM THE SOUTH AS
AN AREA OF LOW PRESSURE IN THE NORTHERN GULF GATHERS STRENGTH AND
LIFTS TOT HE EAST-NORTHEAST TOWARD OUR REGION.

BASED ON SATELLITE AND HOURLY TEMP/DEWPOINTS TRENDS...HAVE ADJUSTED
SKY CONDITIONS AND TEMPS THROUGH THE REMAINDER OF THE NIGHT. -WSS

THURSDAY: SHORTWAVE ENERGY OVER THE CENTRAL PLAINS THIS AFTERNOON
WILL AMPLIFY AS IT TRACKS SOUTHEAST INTO THE DEEP SOUTH LATE TONIGHT
AND THURSDAY...WITH MODEL GUIDANCE INDICATING A CLOSED UPPER LEVEL
LOW IN VICINITY OF THE LA GULF COAST BY 00Z FRIDAY. HEIGHT FALLS AND
DPVA IN ADVANCE OF THE AMPLIFYING UPPER LEVEL WAVE WILL INITIATE
CYCLOGENESIS ALONG THE GULF COAST EARLY THU...WITH THE SFC LOW
TRACKING NORTHEAST TO SAVANNAH BY 00Z FRIDAY. LOW-LEVEL FLOW ALONG
THE CAROLINA COAST WILL GRADUALLY VEER TO THE E/SE AND STRENGTHEN
DURING THE DAY THU...WITH A GRADUAL INCREASE IN THE MAGNITUDE OF
WARM ADVECTION ATOP THE SHALLOW COLD AIRMASS EXTENDING INTO THE
REGION FROM THE N/NE. THE POSITION/MAGNITUDE OF THE ARCTIC HIGH AND
THE PRECISE EVOLUTION OF THE APPROACHING UPPER LEVEL WAVE WILL
LARGELY DICTATE WHEN PRECIP WILL DEVELOP ACROSS THE AREA ON THU. THE
LATEST GUIDANCE SUGGESTS A MORE FAVORABLE SFC HIGH POSITION /COOLER
DRIER AIRMASS/ ADVECTING INTO CENTRAL NC TONIGHT/THU...AND AN UPPER
LEVEL WAVE EVOLUTION THAT SUGGEST A SLOWER ONSET OF PRECIP FROM
SOUTH-NORTH (OR SSE-NNW) DURING THE LATE AFTERNOON AND EARLY EVENING
HOURS...AND THIS IS THE SCENARIO THAT PRECIP TIMING/CHANCES WILL BE
BASED UPON. W/REGARD TO PRECIP TYPE...FORECAST SOUNDINGS INDICATE A
PRONOUNCED WARM NOSE (AT 800-900 MB) ON THU WITH ABOVE FREEZING
SURFACE TEMPS...SUGGESTING RAIN. HOWEVER...WETBULB PROFILES WILL BE
SUPPORTIVE OF SLEET (AT LEAST AT ONSET) AND ANY PRECIP OF SUFFICIENT
RATE/DURATION COULD TILT THERMAL PROFILES IN THAT DIRECTION. WITH
THIS IN MIND...WILL INDICATE A RAIN/SLEET MIX POSSIBLE WITHIN THE
FIRST SEVERAL HOURS OF ONSET...THOUGH THERMAL PROFILES SHOULD
INCREASINGLY SUPPORT ONLY RAIN (FROM S/SE TO N/NW) AS LOW-LEVEL WARM
ADVECTION STRENGTHENS DURING THE AFT/EVE. EVEN IF MIXED PTYPE OCCURS
ON THU...IT WOULD MOST LIKELY BE INTERMITTENT AND OF NO SENSIBLE
IMPACT WITH SFC TEMPS ABOVE FREEZING. EXPECT HIGHS IN THE UPPER 30S
TO NEAR 40F DEPENDING ON THE TIMING OF THICKENING CLOUD COVER AND
THE ONSET OF PRECIP. -VINCENT
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&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 300 PM WEDNESDAY...

...A WINTRY MIX IS LOOKING MORE LIKELY...MAINLY OVER THE NORTHWEST
PIEDMONT THURSDAY NIGHT INTO EARLY FRIDAY...THIS INCLUDES THE
PIEDMONT TRIAD AND ROXBORO...

... RAIN IS EXPECTED ELSEWHERE... BUT MAX MIX WITH A LITTLE SLEET
AND FREEZING RAIN THURSDAY EVENING FROM ALBEMARLE TO RALEIGH TO
ROCKY MOUNT...

...LIQUID EQUIVALENT QPF OF 1 TO 1.25 INCHES EXPECTED...

THE MID/UPPER LOW CURRENTLY EXITING THE TEXAS PANHANDLE IS FORECAST
TO TAKE A SOUTHERLY TRACK ALONG THE GULF COAST THURSDAY NIGHT...
THEN SLOWLY TURN ENE ALONG THE SOUTH CAROLINA COAST FRIDAY...
EXITING THE NC FRIDAY EVENING. THIS SOLUTION IS A PREFERRED BLEND OF
THE 12Z/GFS/ECMWF/UKMET. THE LATEST MODEL GUIDANCE HAS BEEN TRENDING
COLDER WITH LESS OF A WARM NOSE IN THE MID-LEVELS BACK OVER THE
NORTHWEST PIEDMONT FOR THE MAIN PART OF THE EXPECTED PRECIPITATION
EVENT. FOR THE SURFACE LOW PRESSURE DEVELOPMENT/TRACK EXPECTED FROM
THE GULF OF MEXICO NORTHEAST JUST OFFSHORE THE SC/NC COAST THURSDAY
NIGHT AND FRIDAY... IT IS HARD TO ARGUE WITH WPC`S PREFERENCE OF A
BLEND OF THE 12Z/UKMET WITH THE 00Z/ECMWF AND ECMWF ENSEMBLE MEAN
FOR THE FORECAST SOLUTION. THERE HAS BEEN A SLOWING TREND WITH THE
GUIDANCE AND CONFIDENCE HAS ALSO INCREASED WITH BETTER CLUSTERING
FROM THE ENSEMBLE PLOTS.

ANOTHER CRITICAL FEATURE IS THE PRONOUNCED VERY COLD PARENT SURFACE
HIGH PRESSURE THAT IS FORECAST TO BUILD FROM NEW ENGLAND DOWN THE
EASTERN SEABOARD INTO NC/UPSTATE SC LATE WEDNESDAY NIGHT AND
THURSDAY... AND BE IN PLACE THURSDAY EVENING. THIS HIGH IS OF
SUFFICIENT STRENGTH (1040ISH+ MB) AND PREFERRED LOCATION NY/NEW
ENGLAND TO DELIVER COLD DRY AIR INTO OUR REGION AS THE STORM
ARRIVES. ONE QUESTION HAS BEEN HOW QUICKLY THE HIGH WILL RETREAT AND
THIS APPEARS TO BE THURSDAY NIGHT. HOWEVER... CLASSICAL DAMMING IS
EXPECTED TO UNFOLD THURSDAY EVENING AS THE MAIN PRECIPITATION
SATURATES THE COLUMN QUICKLY.

IN ADDITION... THE WARM NOSE ALOFT IS ALSO CRITICAL AS MODELS HAVE
BEEN TRENDING COOLER WITH TIME WITH LESS OF A WARM NOSE REACHING
WELL BACK INTO THE FOOTHILLS/BLUE RIDGE. WE WERE NOT BITING OFF
TOTALLY ON THESE SOLUTIONS AS THERE IS STILL A LOT OF UNCERTAINTY.

IF THESE TRENDS CONTINUE... A WINTER WEATHER ADVISORY OR EVEN A
WINTER STORM WATCH MAY BE NEEDED IN THE NW PIEDMONT FOR THURSDAY
NIGHT INTO EARLY FRIDAY FOR A WINTRY MIXTURE OF MOSTLY FREEZING RAIN
WITH EVEN SOME MEASURABLE SNOW AND SLEET. THE WARM NOSE ALOFT MAY
ACTUALLY EVEN VERIFY LESS INTENSE IF THE LIFT IS STRONG ENOUGH TO
OFFSET THE WAA ABOVE THE NEAR SURFACE COLD NOSE. THIS MAY LEAD TO A
CHANGE TO WET SNOW AT TIMES IN HEAVIER PRECIPITATION. THE TRACK OF
THE MID LEVEL LOW IS ALSO CRITICAL... AND THIS REMAINS WELL SOUTH
AND EAST OF OUR REGION THIS MODEL RUN... SUPPORTING COLDER AIR
ALOFT.

... THE NORTHWEST PIEDMONT TO ROXBORO AND OXFORD...

RIGHT NOW... THE FORECAST 1000/850 AND 850/700 PARTIALS INDICATE
1295-1305M/1545-1555M DURING MUCH OF THE OVERNIGHT PERIOD THURSDAY.
NOMOGRAMS SUGGEST A WINTRY MIXTURE WITH MORE SNOW/SLEET THE LESS THE
WARM NOSE... AND MORE IN THE WAY OF FREEZING RAIN/RAIN IF THE WARMER
NOSE VERIFIES. WE WILL LOOK TO SURFACE WET BULB FORECASTS FOR
PLACEMENT OF THE MOST CRITICAL REGION THAT WOULD LIKELY SEE THE
HIGHEST PROBABILITIES OF THE WINTRY MIXTURE/ICING. CURRENT FORECASTS
INDICATE WET BULBS OF 30-32 FROM NEAR LEXINGTON TO GREENSBORO TO
ROXBORO THURSDAY NIGHT... AND SUB 30 POSSIBLE FROM WINSTON-SALEM AND
THE PTI AIRPORT NORTH AND WEST. THESE WILL BE THE MOST CRITICAL
LOCATIONS FOR POTENTIAL WINTER WEATHER. HERE... WE WILL FORECAST A
MIXTURE OF FREEZING RAIN AND SLEET... POSSIBLY WET SNOW AT TIMES.
GLAZING OF ICE OF 0.1 TO 0.2 POSSIBLE... WITH SNOW AND SLEET OF LESS
THAN AN INCH. THESE ARE PRELIMINARY NUMBERS AND WILL LIKELY CHANGE
AS THE STORM EVOLVES. TEMPERATURES SHOULD FALL TO NEAR THE WET
BULBS... UPPER 20S TO AROUND 30. COLD AIR DAMMING SHOULD BE LOCKED
IN FOR A WHILE. HOWEVER... TEMPS SHOULD SLOWLY RISE TO NEAR OR ABOVE
32 MOST AREAS... INTO THE MID TO UPPER 30S. UNLESS PRECIPITATION
RATES CONTINUE HEAVY... PRECIPIATION SHOULD CHANGE TO RAIN. WET SNOW
CAN NOT BE RULED OUT IN HEAVIER BANDS.

...TO THE SOUTH AND EAST INCLUDING ALBEMARLE TO RALEIGH TO ROCKY
MOUNT... RAIN IS EXPECTED THAT MAY MIX WITH A LITTLE SLEET OR
FREEZING RAIN THROUGH MIDNIGHT... THEN CHANGE TO RAIN AS TEMPS RISE
SLOWLY OVERNIGHT. WET BULBS NEAR 32 DO SUPPORT SOME GLAZING... BUT
ONLY ON ELEVATED SURFACES. RAINFALL RATES SHOULD LIMIT ICING. LOWS
31-32... RISING TO 34-35 OVERNIGHT. RAIN IS EXPECTED FRIDAY. MAY BE
SOME WET SNOW (NON ACCUMULATING) DUE TO THE WET GROUNDS DURING HEAVY
PRECIP BANDS/RATES FRIDAY. HIGHS 37-44.

ALL RAIN IS EXPECTED FROM ROCKINGHAM TO LILLINGTON TO WILSON
SOUTHWARD DURING THE EVENT WITH WET BULBS LIKELY REMAINING ABOVE 33
AND RISING TOWARD 40 OVERNIGHT. RAIN FRIDAY... HIGHS IN THE 40S.

THE BOTTOM LINE AT THIS POINT IS THAT WE ARE CONFIDENT THAT THE
NORTHWEST PIEDMONT HAS THE BEST CHANCE OF A WINTRY MIX... WITH
LESSER CHANCES CLOSER TO THE TRIANGLE AND NIL POINTS SOUTH AND EAST
OF THE ROCKINGHAM TO RALEIGH TO WILSON AREAS.

MODELS HAVE TRENDED TOWARD MORE OF A WINTRY MIX... WITH MORE
FREEZING RAIN AND EVEN SNOW/SLEET OVER THE NW PIEDMONT

CONFIDENCE IN THE PREDOMINATE PRECIP TYPE AND POSSIBLE ACCUMULATIONS
IS STILL LOW GIVEN SOME OF THE DIFFERENCES IN THE EXTEND OF THE
DAMMING... THE SURFACE/850MB LOW TRACK... AND WESTERN
EXTENT/STRENGTH OF THE WARM NOSE.

PRECIPITATION SHOULD END LATE FRIDAY BUT TEMPERATURES SHOULD REMAIN
ABOVE FREEZING FRIDAY AFTERNOON AND NIGHT KEEPING ADDITIONAL
PROBLEMS WITH FREEZING VERY LOW.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 310 PM WEDNESDAY...

DRY AND WARMER THIS WEEKEND. HIGHS RETURN TO THE LOWER TO MID 60S
BOTH SAT-SUN... CONTINUING MONDAY. LOWS GENERALLY MID TO UPPER 30S.

THE NEXT SYSTEM MAY BE DELAYED... BUT TUE-WED THE CHANCE OF RAIN
SHOULD INCREASE AS ANOTHER SOUTHERN BRANCH MID/UPPER LOW APPROACH.
CONTINUED MILD THROUGH MIDWEEK.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AS OF 700 PM WEDNESDAY...

ANY LINGERING LOW CLOUDS ACROSS THE FAR EASTERN PORTIONS OF THE
FORECAST AREA SHOULD CLEAR OUT BEHIND A DEPARTING UPPER LEVEL
DISTURBANCE. THEN...MOSTLY VFR CONDITIONS ARE EXPECTING THROUGH THE
CURRENT TAF PERIOD...ALTHOUGH CONDITIONS WILL BEING TO DETERIORATE
FROM SOUTHEAST TO NORTHWEST THURSDAY AFTERNOON/EVENING. THERE COULD
BE A PERIOD OF SUB-VFR CIGS OVERNIGHT...HOWEVER AM NOT EXPECTING
ANYTHING WIDESPREAD UNTIL THURSDAY AFTERNOON AS A LOW PRESSURE
SYSTEM BEGINS TO TRACK NORTHEAST ALONG THE SOUTHEAST COAST...
SPREADING PRECIP INTO THE AREA. BUT FIRST OVERNIGHT...LIGHT WINDS
WILL BECOME NORTHEAST AT 10-15 MPH IN THE WAKE OF A BACKDOOR COLD
FRONT BETWEEN 02-05Z THIS EVENING...REMAINING NORTHEAST AT 10-15 KT
WITH GUSTS UP TO 20 KT DURING THE DAY THU. AS THE AFOREMENTIONED LOW
PRESSURE SYSTEM APPROACHES THE AREA...PRECIP (POSSIBLY A WINTRY MIX)
WILL OVERSPREAD CENTRAL NC FROM SOUTHEAST TO NORTHWEST THURSDAY
AFTERNOON/EVENING. HAVE ONLY INCLUDED A MENTION OF PRECIP IN KFAY
FOR THIS TAF ISSUANCE AS PRECIP IS EXPECTED TO HOLD OFF UNTIL AFTER
00Z/FRIDAY AT OTHER SITES FURTHER NORTH AND WEST.

OUTLOOK...AVIATION CONDITIONS SHOULD CONTINUE TO DETERIORATE ACROSS
THE REMAINDER OF CENTRAL NC THURSDAY EVENING...WITH WIDESPREAD
ADVERSE AVIATION CONDITIONS PERSISTING THROUGH FRIDAY. A WINTRY MIX
IS POSSIBLE AT ALL TAF SITES...ALTHOUGH FURTHER SOUTH AND EAST
(KFAY, KRWI)...PRECIP IS EXPECTED TO SWITCH OVER TO ALL RAIN. MOSTLY
FROZEN PRECIP IS EXPECTED ACROSS THE NORTHWEST (KINT, KGSO)...WITH
THE TRANSITION LINE BEING SOMEWHERE NEAR KRDU. VFR CONDITIONS ARE
THEN EXPECTED TO RETURN LATE FRIDAY NIGHT INTO SATURDAY AND PERSIST
THROUGH EARLY NEXT WEEK AS HIGH PRESSURE DOMINATES.

&&

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

&&

$$

SYNOPSIS...WSS/VINCENT
NEAR TERM...WSS/VINCENT
SHORT TERM...BADGETT
LONG TERM...BADGETT
AVIATION...KRD