Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 011747
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1245 PM EST SUN MAR 1 2015

.SYNOPSIS...COLD HIGH PRESSURE WILL EXTEND INTO THE REGION THROUGH
THIS EVENING... ALTHOUGH SOME LOW LEVEL MOISTURE WILL SPREAD INTO
THE AREA FROM THE SOUTH RESULTING IN UNSETTLED WEATHER TODAY. A COLD
FRONT WILL MOVE THROUGH THE REGION ON MONDAY. HIGH PRESSURE WILL
BUILD INTO THE REGION LATE TUESDAY AND THEN MOVE OFFSHORE ON
WEDNESDAY AS A STRONG COLD FRONT APPROACHES FROM THE WEST.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 955 AM SUNDAY...

UPDATED: TEMPS ACROSS THE SOUTHERN CWA ARE INCHING INTO THE 32-33F
RANGE CURRENTLY WITH WET BULBS ALSO RIGHT AT THE FREEZING MARK AND
RISING... SO DESPITE ADDITIONAL BANDS OF LIGHT PRECIP TRACKING NE
TOWARD THIS AREA FROM THE SW... BELIEVE WE CAN SAFELY ALLOW THE
ADVISORY TO EXPIRE IN THIS AREA ON SCHEDULE. THE NCDOT HAS NOT
REPORTED ANY SIGNIFICANT TRAFFIC PROBLEMS RECENTLY... HOWEVER IT MAY
STILL TAKE AWHILE FOR RESIDUAL LIGHT ICE GLAZE TO MELT AND WASH
OFF... SO WILL CONTINUE TO ADVISE EXTRA CAUTION. OTHERWISE...
OCCASIONAL LIGHT PRECIP DRIVEN BY STRONG/DEEP MOIST UPGLIDE FROM
285K UP THROUGH AT LEAST 300K PERSISTS OVER CENTRAL NC. THIS UPGLIDE
APPEARS TO BE MAXIMIZED NOW... WITH A SLOW DIMINISHING TREND THROUGH
THE DAY. WILL MAINTAIN HIGH POPS... TRENDING DOWN AND OUT WEST TO
EAST LATER THIS AFTERNOON THROUGH EARLY EVENING. THE OBSERVED 12Z
GSO SOUNDING SHOWS WELL THE WARM NOSE ALOFT AND LOW LEVEL COLD
AIR... INDICATING A CONTINUED THREAT OF FREEZING RAIN OVER THE
REMAINDER OF CENTRAL NC WHERE TEMPS NOW SIT AT 28-31 WITH
SUBFREEZING WET BULBS. MOST ACCRUAL HAS BEEN ON ELEVATED OBJECTS AND
BRIDGES/OVERPASSES... WITH GROUND-ADJACENT ROAD SURFACES JUST WET IN
MANY AREAS. WITH THE LOSS OF SUPPORT FROM THE PARENT HIGH TO PROVIDE
A STEADY FEED OF LOW LEVEL COLD AIR... RESULTING IN A LIMITATION OF
ICE ACCRUAL BY LATENT HEAT RELEASE... NOT ALL OF THE ADDITIONAL
PRECIP WILL RESULT IN ICING... AND OUTSIDE OF THE FAR NRN SECTIONS
WHERE TEMPS ARE COLDEST... MOST AREAS WILL SEE ONLY A TRACE AMOUNT
OF ADDITIONAL ICING. WILL MAINTAIN THE CURRENT FORECAST SLOW TREND
OF TEMPS RISING TO AT/ABOVE FREEZING FROM SOUTH/SE TOWARD THE
NORTH/NW FOR THE REST OF THE DAY. NO CHANGES TO REMAINING ADVISORY
AT THIS TIME. -GIH

PREVIOUS DISCUSSION FROM 345 AM: TODAY...RIDGE EXTENDING FROM PARENT
ARCTIC HIGH OVER THE NORTHERN MID ATLANTIC MAINTAIN A SUPPLY OF COLD
DRY AIR INTO CENTRAL NC THIS MORNING. RETURN SLY FLOW ON THE
BACKSIDE OF THE RETREATING 925-850MB HIGH OFF THE SE U.S. COAST
ADVECTING OVER THE COLD STABLE AIR MASS AT THE SURFACE. THIS HAS
RESULTED IN PATCHES OF LIGHT PRECIP TO BEAK OUT OVER OUR FAR
SOUTHERN COUNTIES SHORTLY AFTER MIDNIGHT ...AND BEGINNING TO SPREAD
ACROSS THE WESTERN PIEDMONT AT 08Z. WITH SFC DEWPOINTS SPREAD OF 12-
16 DEGREES ACROSS THE PIEDMONT AND NORTHERN COASTAL
PLAIN...EVAPORATIVE COOLING SHOULD DROP SFC TEMPS TO BELOW FREEZING
FOR SEVERAL HOURS ONCE THE PRECIPITATION SETS IN. OVER THE FAR SOUTH-
SE...THIS TIME BELOW FREEZING SHOULD BE NO MORE THAN A COUPLE OF
HOURS (IF THAT).

APPEARS BEST THREAT FOR ICE ACCRUAL OF A TENTH OF AN INCH OR A
LITTLE MORE WILL BE ACROSS THE FAR NORTHERN PIEDMONT/VA BORDER
COUNTIES...AND INTO THE NORTHERN SECTIONS OF FORSYTH...GUILFORD AND
ALAMANCE COUNTIES. ELSEWHERE...EXPECT ENOUGH ICE ACCRUAL ON EXPOSED
SURFACE OBJECTS AS WELL AS BRIDGES AND OVERPASSES TO FORM A THIN
GLAZE...ENOUGH TO MAKE TRAVEL HAZARDOUS IN SPOTS ACROSS THE PIEDMONT
THIS MORNING.

FAIRLY SUBSTANTIAL WARM NOSE ALOFT (APPROACHING 8 DEGREES C IN THE
NW PIEDMONT BY LATE MORNING) MAY BE ENOUGH TO OVERCOME THE SUB
FREEZING CONDITIONS AT THE SURFACE. THUS WHILE SFC TEMPS IN THE
NORTHERN PIEDMONT MAY BE 31-32 DEGREES BY MID DAY...ADDITIONAL ICE
ACCRUAL WILL BE SEVERELY LIMITED. PLAN TO MAINTAIN ADVISORY ACROSS
THE FAR NORTH-NW UNTIL 4 PM BUT WILL ASSESS TEMP RESPONSE LATER THIS
MORNING WITH A POSSIBILITY OF ENDING THE ADVISORY A FEW HOURS
EARLIER. ELSEWHERE CURRENT ADVISORY END TIMES APPEAR ON TARGET.

MAX TEMPS THIS AFTERNOON DEPENDENT UPON ON HOW EXTENSIVE THE PRECIP
BECOMES AND WHEN IT TAPERS OFF. COUNTING ON PRECIP LINGERING THROUGH
A GOOD PART OF THE AFTERNOON ACROSS THE EAST SO HAVE LOWERED TEMPS
THERE A FEW DEGREES FROM PREVIOUS FORECAST. CONVERSELY...HAVE
ADJUSTED MAX TEMPS UP A DEGREE OR TWO ACROSS THE WEST-SW WHERE
PRECIP MAY TAPER OFF BY EARLY-MID AFTERNOON.

&&

.SHORT TERM /TONIGHT AND MONDAY/...
AS OF 345 AM SUNDAY...

TONIGHT...EXTENSIVE LOW CLOUDS AND AREAS OF FOG EXPECTED WHILE A SLY
SFC WIND WILL BEGIN TO STIR AS A COLD FRONT APPROACHES FROM THE WEST-
NW. THESE CONDITIONS SHOULD CAUSE TEMPS TO HOLD STEADY OVERNIGHT.
MIN TEMPS IN THE MID-UPPER 30S.

MONDAY...SFC COLD FRONT SHOULD CROSS THE AREA IN THE MORNING.
APPEARS MOISTURE DEPTH FAIRLY LIMITED TO GENERATE ANY PRECIP ACROSS
THE NW BUT MAY BE ENOUGH ACROSS THE FAR SOUTH-SE TO DEVELOP A FEW
PATCHES OF LIGHT RAIN. NWLY FLOW BEHIND THE FRONT WILL AID TO ADVECT
A DRIER AIR MASS IN THE REGION. THIS WILL SLOWLY ERODE CLOUD
COVERAGE FROM THE NW DURING THE AFTERNOON. SHOULD SEE TEMPS REBOUND
INTO THE LOW AND MID 50S WITH PARTIAL SUNSHINE OVER MOST OF THE
PIEDMONT BY AFTERNOON (LESS SO ACROSS THE FAR SOUTH-SE). FAVORED
COOLER NAM MOS GUIDANCE VERSUS THE WARMER MOS GUIDANCE.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
AS OF 320 PM SUNDAY...

MONDAY NIGHT AND TUESDAY: SURFACE HIGH PRESSURE LOCATED JUST TO THE
NORTH OF CENTRAL NC AND AND MID LEVEL RIDGING EXTENDING INTO THE
AREA FROM THE SOUTH WILL BOTH QUICKLY SHIFT EASTWARD ON MONDAY NIGHT
INTO TUESDAY. HOWEVER... THE LINGERING COLD DRY SURFACE AIR
DEPOSITED BY THE SURFACE HIGH WILL AGAIN SET THE STAGE FOR AN INSITU
CAD EVENT ON TUESDAY INTO TUESDAY NIGHT... POSSIBLY LINGERING INTO
WEDNESDAY MORNING ACROSS THE FAR NORTHWEST PIEDMONT. WARM MOIST AIR
WILL INCREASING IN SOUTHERLY TO SOUTHWESTERLY FLOW ALOFT. GIVEN THIS
AND THE LINGERING COLD SURFACE AIRMASS... WE SHOULD SEE SOME
ISENTROPICALLY DRIVEN PRECIP DEVELOP TUESDAY MORNING INTO THE
AFTERNOON. TUESDAY MORNING LOW TEMPS ARE EXPECTED TO BE AROUND 30
NORTH TO NEAR 40 SOUTH. MODELS CONTINUE TO BRING THE LIGHT PRECIP IN
AFTER SURFACE TEMPS AND DEWPOINTS INCREASE ENOUGH TO AVOID AND
NUISANCE FREEZING RAIN. HOWEVER... HIGH TEMPS WILL BE WELL BELOW
NORMAL AND GREATLY AFFECTED BY THE CAD AIRMASS. MAV STATISTICAL
GUIDANCE APPEARS TO BE WAY TOO WARM FOR TUESDAY... WITH THE RAW GFS
TEMPS CLOSER TO MET GUIDANCE VALUES. FOR NOW WILL LOWER TEMPS
FURTHER... AND THIS MAY NOT EVEN BE FAR ENOUGH. WILL WO WITH HIGH
TEMPS RANGING FROM THE UPPER 30S NORTH TO NEAR 50 IN THE FAR
SOUTHEAST.

TUESDAY NIGHT THROUGH THURSDAY NIGHT: ANOTHER STRONG ARCTIC COLD
FRONT WILL APPROACH THE REGION ON TUESDAY NIGHT... BEFORE SLOWLY
MOVING ACROSS THE AREA WEDNESDAY INTO THURSDAY MORNING. THE FRONT IS
EXPECTED TO BECOME PARALLE WITH THE MID LEVEL FLOW AS THE MID/UPPER
LEVEL TROUGH BECOMES MORE OF A FULL LATITUDE TROUGH... WHICH
APPEARS TO PHASE SOME THE THE SOUTHERN STREAM ENERGY WITH THE
NORTHERN STREAM... RESULTING IN A DEEP FETCH OF SOUTHWESTERLY MID
LEVEL FLOW... ALONG WITH SEVERAL SURFACE LOWS TRACKING ALONG THE
FRONT FROM TIME TO TIME. MOST OF THE SHOWERS WILL BE ALONG AND
BEHIND THE FRONT... MAINLY FROM WEDNESDAY MID-MORNING INTO THE
AFTERNOON UNTIL LATE THURSDAY (WITH A GOOD CHANCE OF PRECIP...
POSSIBLY SOME HEAVY AMOUNTS OF RAIN). IN ADDITION... MODELS HAVE
TRENDED FASTER WITH SURGING THE STRONG/DEEP COLD LOW LEVEL AIRMASS
INTO THE REGION. IF THIS WERE TO OCCUR... WE COULD POSSIBLE SEE SOME
WINTRY P-TYPES ON THURSDAY. HOWEVER... GIVEN WE ARE STILL TALKING
ABOUT DAY 5 IN THE FORECAST AND WE ARE NOW IN THE MONTH OF MARCH...
WILL WAIT TO ADD ANY NON-LIQUID P-TYPE TO THE FORECAST. DRY WEATHER
IS EXPECTED TO RETURN FOR AT LEAST FRIDAY. HOWEVER...  THE SYNOPTIC
PATTERN MAY REMAIN CONDUCIVE FOR WAVES OF LOW PRESSURE TO DEVELOP
AND TRACK ALONG THE FRONT... WHICH IS EXPECTED TO BE LOCATED OFF THE
CAROLINA COAST LATE WEEK INTO THE WEEKEND. THUS... WE COULD
CONCEIVABLY SEE SOME PRECIP IF ONE SUCH SYSTEM DEVELOPS NEXT WEEKEND.

TEMPS DURING THE MEDIUM RANGE WILL INCLUDE SOME DECENT SWINGS...
WITH HIGHS TEMPS WEDNESDAY IN THE 60S AND 70S... THURSDAY 40S AND
50S (MAYBE COLDER)... WITH FRIDAY BACK IN THE 40S (WITH MAYBE SOME
30S EVEN). WE WILL SEE SOME MODERATING BY SATURDAY... GENERALLY BACK
INTO THE 50S... GIVEN WE REAMIN DRY. LOWS WILL FOLLOW A SIMILAR
PATTERN. AS MENTIONED ABOVE...  ALL PRECIP AS OF NOW APPEARS TO BE
IN THE FORM OF LIQUID FOR THE MEDIUM RANGE... OUTSIDE OF *MAYBE* A
BRIEF PERIOD AS THE PRECIP ENDS ON THURSDAY.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
AS OF 1245 PM SUNDAY...

PRIMARY AVIATION CONCERNS NEXT 24 HRS: CONTINUED IFR/LIFR CIGS AND
MVFR/IFR VSBYS THROUGH TONIGHT... AND BORDERLINE LOW LEVEL WIND
SHEAR THIS EVENING/TONIGHT.

WIDESPREAD IFR/LIFR CONDITIONS PERSIST OVER CENTRAL NC TAF SITES
THIS AFTERNOON... ALONG WITH PATCHES OF RAIN (FAY/RDU) OR FREEZING
RAIN (RWI/INT/GSO). THIS FREEZING RAIN AT RWI/INT/GSO WILL TREND TO
JUST RAIN THIS AFTERNOON... FIRST AT RWI THEN AT GSO AND INT. ALL
LOCATIONS SHOULD BE JUST RAIN BEFORE 21Z. PERIODS OF RAIN WILL TAPER
OFF AT INT/GSO BY 22Z THIS AFTERNOON... AT RDU BY 00Z THIS
EVENING... AND AT FAY/RWI BY 04Z LATE THIS EVENING. WITH FAIRLY
LIGHT SURFACE WINDS OVERNIGHT AND A MOIST GROUND... CONFIDENCE IS
HIGH THAT IFR/LIFR CONDITIONS WILL HOLD THROUGH AT LEAST 12Z MON AT
ALL TAF SITES. AS A WEAK FRONT DROPS SOUTHEAST INTO THE AREA
MONDAY... CAUSING SURFACE WINDS TO SHIFT FROM LIGHT SW TO BE FROM
THE NW... THESE LOW CLOUDS/FOG WILL SCOUR OUT GRADUALLY TO VFR BY
THE 16Z-18Z MONDAY TIME FRAME AT INT/GSO... WITH LOWER CONFIDENCE IN
THIS OCCURRING PRIOR TO 18Z AT RDU/RWI/FAY. LOW LEVEL WIND SHEAR
THREAT REMAINS MARGINAL AND FOCUSED AFTER MIDNIGHT TONIGHT AT
FAY/RDU/RWI... AS 1000-1500 FT AGL WINDS BECOME WESTERLY AT 25-30
KTS.

LOOKING BEYOND 18Z MON... VFR CONDITIONS SHOULD PERSIST FROM EARLY
TO MID AFTERNOON MONDAY THROUGH MONDAY NIGHT... AS THE SURFACE FRONT
SETTLES ALONG THE SRN NC BORDER WHILE HIGH PRESSURE NOSES IN FROM
THE NORTHWEST. HOWEVER... A DISTURBANCE ALOFT RIDING ALONG THE
SURFACE FRONT WILL BRING A THREAT OF MVFR/IFR CONDITIONS STARTING
LATE MONDAY NIGHT (INT/GSO) OR TUE AFTERNOON (RDU/RWI/FAY)... ALONG
WITH A LLWS RISK. THESE SUB-VFR CONDITIONS SHOULD GIVE WAY TO VFR
CONDITIONS AT FAY THEN AT RWI/RDU WED AS A WARM FRONT MOVES
NORTHWEST THROUGH THE AREA WITH STRENGTHENING SW WINDS... BUT SUB-
VFR CONDITIONS MAY HOLD IN LONGER AT INT/GSO. THIS WARM FRONT WILL
DROP BACK DOWN SOUTHEAST THROUGH THE AREA AS A COLD FRONT LATE WED
OR WED NIGHT... TURNING SURFACE WINDS BACK AROUND TO
NORTH/NORTHEASTERLY FOR THU WITH WIDESPREAD RAIN AND SUB-VFR
CONDITIONS. VFR CONDITIONS SHOULD RETURN TO NORTHERN SECTIONS
(RDU/RWI/INT/GSO) BY THURSDAY NIGHT/FRIDAY. -GIH

&&

.RAH WATCHES/WARNINGS/ADVISORIES...

WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS EVENING FOR
NCZ007-021>023-038-039.

&&

$$
SYNOPSIS...RAH
NEAR TERM...HARTFIELD/WSS
SHORT TERM...WSS
LONG TERM...BSD
AVIATION...HARTFIELD



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