Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 271208
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
708 AM EST FRI FEB 27 2015

.SYNOPSIS... COLD HIGH PRESSURE OVER THE CENTRAL PLAINS WILL BUILD
INTO THE MID ATLANTIC TODAY THROUGH SATURDAY.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
AS OF 300 AM FRIDAY...

...WINTER WEATHER ADVISORY FOR BLACK ICE IN EFFECT THROUGH 10 AM
THIS MORNING...

PLAN TO MAINTAIN CURRENT WSW FOR BLACK ICE AS IS UNTIL 10 AM. WITH
TEMPS ACROSS THE REGION CURRENTLY IN THE 25-30 DEGREE
RANGE...REFREEZING OF MELTED ICE/SNOW LIKELY UNDERWAY. EVENING CREW
ON THEIR WAY HOME EARLIER REPORTED SCATTERED SLICK SPOTS ON AREA
ROADWAYS HAD DEVELOPED. TOYED WITH THE IDEA OF A NPW FOR FREEZING
FOG ADVISORY AS VISIBILITIES HAVE LOWERED TO AT OR BELOW A QUARTER
OF A MILE AT A FEW SITES ACROSS THE NORTH. HOWEVER...AFTER
COORDINATING WITH SURROUNDING WFOS...WANT THE EMPHASIS TO BE MORE ON
THE BLACK ICE VERSUS THE DENSE FOG SO WILL INCORPORATE THE MENTION
OF DENSE/FREEZING FOG IN THE UPDATED WSW STATEMENT.

OTHERWISE...FAST SW FLOW ALOFT WILL MAINTAIN A DECK OF HIGH LEVEL
CLOUDS OVER THE REGION  WHILE THE APPROACH OF A S/W CROSSING THE
LOWER OH VALLEY WILL CAUSE PERIODS OF MID CLOUDS AS WELL. LIFT
APPEARS TO BE ENOUGH TO GENERATE CLOUDS BUT NOT ENOUGH TO GENERATE
PRECIPITATION THOUGH COULD SEE A POCKET OF DRIZZLE OR SNOW FLURRIES
THIS AFTERNOON WHEN THE TAIL END OF THE S/W CROSSES OUR REGION.

LOW LEVEL THICKNESSES THIS AFTERNOON AVERAGE 50-60M BELOW
AVERAGE...SUPPORTIVE OF MAX TEMPS WELL BELOW NORMAL FOR LATE
FEBRUARY. FAVOR MAX TEMPS ON THE COOL SIDE OF MOS GUIDANCE. EXPECT
MAX TEMPS IN THE UPPER 30S TO AROUND 40 NORTH TO THE LOW-MID 40S
SOUTH.

THE FOREMENTIONED S/W WILL USHER A SFC COLD FRONT ACROSS CENTRAL NC
LATE THIS AFTERNOON/EARLY THIS EVENING. THE AIR MASS BEHIND THIS SFC
FEATURE WILL BE NOTICEABLY DRIER AND COOLER. EXPECT SOME MINOR
DECREASE IN CLOUDINESS OVERNIGHT BUT NOT EXPECTING TOTALLY CLEAR
SKIES. THICKNESSES IN THE 1260-1265M RANGE HISTORICALLY SUGGEST MIN
TEMPS CLOSE TO 20 DEGREES. FAVOR THE COOLER MAV GUIDANCE VERSUS THE
WARMER MET.

SATURDAY...1040+MB HIGH CENTERED OVER SOUTHERN NEW ENGLAND WILL NOSE
SOUTHWARD INTO THE CAROLINAS. THIS DRY AIR RIDGE AND ACCOMPANYING
850MB THERMAL TROUGH WILL RESULT IN ANOTHER DAY OF WELL BELOW NORMAL
TEMPS. FAVOR THE COOLER MAV GUIDANCE THOUGH IF PEEKS OF SUN MORE
PREVALENT THEN CURRENT THINKING...AFTERNOON TEMPS COULD END UP BEING
3-4 DEGREES WARMER THAN FORECAST.

THE NEXT LOW PRESSURE SYSTEM WILL BE DEVELOPING/APPROACHING FROM THE
WEST-SW SATURDAY NIGHT. MEANWHILE DRY AIR SFC RIDGE WILL BEGIN TO
SHIFT OFFSHORE BUT STILL MAINTAIN A PRESENCE ACROSS OUR REGION. MOS
GUIDANCE...MAINLY THE MAV...APPEARS TOO COLD CONSIDERING THE
INCREASING/THICKENING CLOUD COVERAGE. WHILE ISENTROPIC UPGLIDE WILL
BE ON THE INCREASE TOWARD DAYBREAK SUNDAY...LIFT APPEARS TOO WEAK TO
GENERATE PRECIPITATION. THUS WILL MAINTAIN A DRY FORECAST. MIN TEMPS
UPPER TEENS TO AROUND 20 NE TO THE MID 20S FAR SOUTH AND WEST.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
AS OF 300 AM FRIDAY...

SURFACE HIGH PRESSURE OVER THE AREA SUNDAY MORNING WILL QUICKLY
SHIFT OFFSHORE BY SUNDAY AFTERNOON AS A QUICK MOVING S/W DISTURBANCE
MOVES EASTWARD FROM THE NORTHERN PLAINS INTO THE GREAT LAKES
REGION... WITH AND ASSOCIATED COLD FRONT APPROACHING THE AREA FROM
THE NORTHWEST. IN RESPONSE TO THE APPROACHING SYSTEM... A MOIST
SOUTH/SOUTHWESTERLY LOW LEVEL FLOW ATOP A DEPOSITED COLD SURFACE
AIRMASS WILL INCREASE THROUGHOUT THE DAY ON SUNDAY... WITH PRECIP
POSSIBLY DEVELOPING ACROSS WESTERN PORTIONS OF THE CWA. THE LATEST
NAM CONTINUES TO BE AN OUTLIER IN BRING PRECIP IN DURING THE EARLY
MORNING HOURS ON SUNDAY. IF THIS INDEED OCCURRED THEN WE MAY HAVE
SOME P-TYPE ISSUES (GENERALLY SLEET AND/OR FREEZING RAIN) ACROSS
MAINLY WESTERN PORTIONS OF THE AREA. HOWEVER... WITH BOTH THE GFS
AND ECMWF REMAINING DRY UNTIL THE AFTERNOON ACROSS THE WESTERN
PORTION OF THE AREA... WILL ONLY SHOW A CHANCE OF RAIN ACROSS THE
WESTERN PIEDMONT DURING THE AFTERNOON HOURS (CHILLY RAIN THOUGH).
NONETHELESS...  WITH THE SURFACE RIDGE AXIS EXTENDING BACK INTO THE
AREA AFTER IT MOVES OFFSHORE ALONG WITH SOME PRECIP POSSIBLE ACROSS
AT LEAST WESTERN PORTIONS OF THE AREA BY AFTERNOON EXPECT SKIES WILL
BE CLOUDY WITH HIGHS EXPECTED TO BE WELL BELOW NORMAL AGAIN. FOR NOW
WILL ONLY LOWER PREVIOUS HIGH TEMPS BY A COUPLE OF DEGREES. THIS
YIELDS HIGHS RANGING FROM THE UPPER 30S NW TO THE MID TO UPPER 40S
SE.

THE SURFACE COLD FRONT WILL APPROACH AND MOVE THROUGH CENTRAL NC ON
SUNDAY NIGHT INTO MONDAY... HELPING TO SOUR OUT ANY COLD AIR DAMMING
AIRMASS THAT IS ABLE TO DEVELOP. HOWEVER... AHEAD OF THE FRONT
EXPECT WE WILL SEE POCKETS OF LIGHT RAIN AND DRIZZLE TO DEVELOP ON
SUNDAY NIGHT... WITH POSSIBLY A BAND OF LIGHT SHOWERS ON  MONDAY
ALONG AND AHEAD OF THE COLD FRONT. LOWS AND HIGHS WILL BE TRICKY AND
DEPEND ON THE EXTENT OF THE CAD AND HOW QUICKLY THE FRONT MOVES
THROUGH. FOR NOW WILL TREND TEMPS COOLER. LOW TEMPS MONDAY MORNING
RANGING FROM THE MID 30S NORTH/NORTHWEST TO THE LOWER 40S SE. HIGHS
MONDAY IN THE LOWER TO MID 50S (WITH A HIGH BUST POTENTIAL...
ESPECIALLY IF THERE IS A LINGERING CAD BOUNDARY ACROSS THE AREA).

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
AS OF 320 AM FRIDAY...

STRONG SURFACE HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE
NORTHWEST ON MONDAY NIGHT INTO TUESDAY... WITH THE AFOREMENTIONED
SURFACE FRONT SETTLING TO THE SOUTH OF THE AREA. MEANWHILE... MID
LEVEL RIDING WILL BUILD ACROSS THE AREA AS THE MID LEVEL FLOW ACROSS
THE CONUS BECOMES MORE AMPLIFIED. THE LATEST GFS AND ECMWF CONTINUE
TO DISAGREE WITH HOW QUICKLY WE WILL SEE A MOISTENING SOUTHERLY
RETURN FLOW DEVELOP ACROSS THE AREA... POSSIBLY RESULTING IN THE
DEVELOPMENT OF ANOTHER CAD AIRMASS. GIVEN WPC CONTINUES TO TREND
TOWARDS THE WETTER SIDE OF THE GUIDANCE... WILL CONTINUE TO KEEP
SKIES CLOUDY... WITH A CONTINUED CHANCES FOR PRECIP (WHICH IS MORE
IN LINE WITH THE LATEST GFS). GIVEN THIS WILL KEEP TEMPS ON THE
COOLER SIDE OF GUIDANCE AND GO WITH HIGH TEMPS ON TUESDAY RANDING
FROM THE LOWER TO MID 40S NW TO THE LOWER TO MID 50S SE... WITH LOW
TEMPS TUESDAY MORNING IN THE MID 30S NORTH TO AROUND 40 SOUTH.

AS THE NEXT SURFACE FRONT BEGINS TO APPROACH THE REGION FROM THE
WEST... EXPECT ANY LINGERING CAD AIRMASS TO BEGIN TO ERODE. THUS...
LOW TEMPS ON TUESDAY NIGHT/WEDNESDAY MORNING COULD OCCUR EARLY IN
THE NIGHT... WITH POSSIBLE RISING TEMPS OVERNIGHT. WILL NOT GET THAT
DETAILED IN THE GRIDDED FORECAST AT THAT TIME GIVEN UNCERTAINTY OVER
IF WE WILL SEE A CAD AIRMASS EVEN DEVELOP. LOWS TUESDAY
NIGHT/WEDNESDAY MORNING IN THE LOWER 40S NW TO THE LOWER 50S SE. THE
AFOREMENTIONED NEXT SURFACE COLD FRONT WILL SLOWLY MOVE ACROSS THE
REGION WEDNESDAY INTO THURSDAY MORNING AS THE SURFACE FRONT BECOMES
MORE PARALLE TO THE MID LEVEL FLOW. GIVEN THE SLOW MOVING FRONT WITH
ALONG WITH A GOOD TAP OF MOISTURE FROM THE GULF OF MEXICO WE COULD
SEE DECENT RAINFALL TOTALS WEDNESDAY (MAINLY NORTHWEST PIEDMONT
WEDNESDAY DURING THE DAY... AT THIS TIME) INTO THURSDAY. IN
ADDITION... TEMPS AHEAD OF THE FRONT ARE EXPECTED TO REBOUND QUITE
NICELY (WITH THE CAD AIRMASS EXPECTED TO ERODE PRIOR TO PASSAGE OF
THE COLD FRONT EVEN IN THE NW) TO AROUND 60/LOWER 60S NW TO THE
LOWER TO MAYBE EVEN MID 70S SE. HIGHS AND LOWS ON THURSDAY WILL
DEPEND ON HOW QUICKLY THE FRONT MOVES THROUGH THE REGION. FOR NOW
WILL GO WITH LOWS THURSDAY MORNING IN THE MID 40S TO LOWER 50S...
WITH HIGHS IN THE 50S TO LOWER 60S.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AS OF 708 AM FRIDAY...

MAIN AVIATION HAZARD THROUGH MID MORNING WILL BE IFR/LIFR VISIBILITY
DUE TO FREEZING FOG. THE PROBABILITY OF LIFR VISIBILITY IS HIGHEST
IN THE COASTAL PLAIN AND THE NORTHERN PIEDMONT INCLUDING IN
VICINITY OF KRWI...KINT...KGSO...AND KRDU. VISIBILITIES WILL IMPROVE
BETWEEN 12Z-14Z.

OTHERWISE...EXPECT A DECK OF HIGH END MVFR/LOW END VFR CEILINGS
AROUND MID DAY THROUGH AFTERNOON AS AN UPPER LEVEL DISTURBANCE
SKIRTS ACROSS THE REGION. SFC WINDS WILL GO FROM LIGHT AND VARIABLE
EARLY TO NORTHERLY NEAR 10KTS BY LATE MORNING-EARLY AFTERNOON.

MOISTURE TRAPPED BELOW A DEVELOPING SUBSIDENCE INVERSION MAY CAUSE
A DECK OF STRATUS TO MOVE ACROSS CENTRAL NC OVERNIGHT...RESULTING
IN A PERIOD OF MVFR/IFR CEILINGS. OTHERWISE VFR CONDITIONS WILL
RETURN SATURDAY AND RETURN SATURDAY NIGHT AS HIGH PRESSURE BECOMES
ESTABLISHED ACROSS THE AREA.

AS THE HIGH SHIFTS EAST SUNDAY...SOUTHERLY RETURN FLOW WILL ADVECT A
WARMER MOIST AIR MASS INTO OUR AREA...RESULTING IN AN INCREASED
PROBABILITY OF MVFR CEILINGS ALONG WITH PATCHES OF RAIN. THE ADVERSE
AVIATION WEATHER CONDITIONS ARE EXPECTED TO PERSIST INTO TUESDAY.

&&

.RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY IN
EFFECT THROUGH 10 AM EST THIS MORNING FOR NCZ007>011-021>028-038>043-
073>078-083>086-088-089.

&&

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


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