Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 010602
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
100 AM EST SUN MAR 1 2015

.SYNOPSIS...
WHILE COLD HIGH PRESSURE WILL EXTEND ACROSS THE AREA
TODAY...INCREASING MOISTURE WILL HELP PROVIDE FOR UNSETTLED WEATHER.
A COLD FRONT WILL MOVE THROUGH THE AREA MONDAY...FOLLOWED BY HIGH
PRESSURE FOR TUESDAY...BEFORE ANOTHER COLD FRONT MOVES INTO THE
REGION LATE WEDNESDAY.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 1030 PM SATURDAY...

STRONG 1043MB HIGH CENTERED OVER THE DELMARVA HAS SUPPLIED A VERY
DRY AIRMASS FOR CENTRAL NC THIS EVENING WITH DEWPOINTS WELL INTO THE
TEENS.  MODELS HAVE STRUGGLED WITH THE AIRMASS A BIT...WITH THE GFS
AND ECMWF BEING TO COLD THIS EVENING...BUT THE WETBULB FREEZING LINE
IS SUPPRESSED WELL SOUTH TO THE NC/SC BORDER.  EARLY ON... RADAR
RETURNS HAVE BEEN CONFINED TO CENTRAL AND EASTERN SC AND APPEAR TO
BE INITIALLY DRIVEN BY WARM ADVECTION UP NEAR 700MB.  DRIER AIR
BELOW HAS KEPT THE PRECIP SPOTTY BUT THERE ARE SOME REPORTS OF LIGHT
RAIN IS SC.  WITH TIME...THE WARM ADVECTION AND ISENTROPIC LIFT WILL
INCREASE ACROSS SOUTHERN AND WESTERN NC IN RESPONSE TO AN UPPER
LEVEL JET CROSSING THE MID-MISSISSIPPI VALLEY REGION. DRY AIR SHOULD
ALSO KEEP PRECIP SPOTTY INITIALLY...BUT THE LOW-LEVEL JET IS
FORECAST TO INTENSIFY TO 40-50KT FROM THE PIEDMONT NORTH INTO VA
AFTER 09Z...SO EXPECT PRECIP TO FILL IN AND QPF TO INCREASE MORE
TOWARD THE 12-15Z TIME FRAME.  MOISTURE NEVER REALLY REACHES ABOVE
-6 TO -8C...SO WHILE BRIEF PERIODS OF SLEET ARE POSSIBLE...FREEZING
RAIN WILL BE THE PREDOMINATE PTYPE. MODEL QPF RANGES A TENTH OF AN
INCH THROUGH 18Z ON THE ECMWF TO UP TO A QUARTER OF AN INCH ON THE
NAM.  THE GFS IS OVERDONE UPSTREAM OVER GEORGIA...SO HAVE DISCOUNTED
IT FOR NOW.  AS YOU GO EAST...CONFIDENCE IN MEASURABLE PRECIP IS
MUCH LOWER TONIGHT AS MOISTURE IS SHALLOWER...AND BY THE TIME BETTER
PRECIP SPREADS EAST TOMORROW...WARMING SHOULD ALLOW TEAMS AND
WETBULB VALUES TO RISE ABOVE 32 BY MID-MORNING.  THE MAIN CONCERN
AND CHANGE IN THE FORECAST THIS EVENING IS IN THE NORTHERN PIEDMONT
AND NORTHERN COASTAL PLAIN WHERE INCREASING QPF MAY OVERLAP WITH SUB-
FREEZING TEMPS FOR A LONGER PERIOD THAN PREVIOUSLY EXPECTED SUNDAY
MORNING.  GENERALLY STILL EXPECT A TENTH OF AN INCH OF ICE AT MOST
ACROSS THE NORTHWEST PIEDMONT...BUT SOME AREAS OVER THE NORTHERN
PIEDMONT COULD SEE A TENTH OF AN INCH AS WELL.

GIVEN THE QUESTIONABLE MODEL PERFORMANCE AND CONSISTENCY WITH THIS
EVENT SO FAR...CONFIDENCE IN THE WINTER WEATHER ADVISORY IS BEST
ONLY IN THE WEST AND MUCH LOWER IN THE EAST.  HAVE ELECTED TO EXPAND
THE ADVISORY TO COVER ALL OF CENTRAL NC...AND WILL MESH THE NEW
AREAS WITH THE PREVIOUS ADVISORY SEGMENTS...ENDING FROM NORTH TO
SOUTH THROUGH THE MORNING HOURS.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
AS OF 220 PM SATURDAY...

THE APPROACHING UPPER LEVEL TROUGH WEAKENS AS IT MOVES THROUGH
CENTRAL NC ON MONDAY. LATEST MODEL RUNS INDICATE MONDAY WILL BE
MOSTLY DRY...WITH A SLIGHT CHANCE OF SOME LIGHT PRECIPITATION EARLY
IN THE DAY...DRYING INTO THE AFTERNOON AS THE RAINFALL ALONG THE
FRONT DISSIPATES OVER THE MOUNTAINS. THE COLD FRONT WILL TILT TO A
MORE WEST TO EAST ORIENTATION AND SLIDE THROUGH THE AREA BY MONDAY
EVENING. SURFACE HIGH PRESSURE WILL BUILD IN THEREAFTER AND REMAIN
THROUGH MONDAY NIGHT. ALTHOUGH TEMPERATURES SHOULD RISE DURING THE
DAY GIVEN GRADUALLY CLEARING SKIES AND THUS GOOD SUNSHINE...THE
INCREASES WILL BE GREATEST ACROSS THE SOUTH WHERE THE FROPA HAPPENS
LATER. HIGHS WILL RANGE FROM UPPER 40S ACROSS THE NORTH TO UPPER 50S
IN THE SOUTH...ALTHOUGH THEY ARE HIGHLY DEPENDENT ON THE TIMING OF
THE FRONT. OVERNIGHT LOWS SHOULD BE IN TEH UPPER 20S NORTH TO UPPER
30S SOUTH.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 300 PM SATURDAY...

TUESDAY THROUGH THURSDAY NIGHT: THE UPPER LEVEL TROUGH ASSOCIATED
WITH AN UPPER LEVEL LOW OVER CENTRAL CANADA ON TUESDAY WILL EXTEND
SOUTHWEST THROUGH THE INTERMOUNTAIN WEST AND INTO THE DESERT
SOUTHWEST. AT THE SURFACE...THE COLORADO LOW THAT DEVELOPS ON MONDAY
WILL BEGIN ITS TREK EASTWARD THROUGH THE MIDWEST MONDAY NIGHT...
SLIDING NORTHEAST INTO THE GREAT LAKES ON TUESDAY. THE ASSOCIATED
COLD FRONT THAT DEVELOPS WILL EXTEND FROM APPROX THE CENTRAL GREAT
LAKES TO THE ARKLATEX BY LATE TUESDAY.

ACROSS CENTRAL NC...THE CAD WEDGE THAT SET UP MONDAY NIGHT WILL
LINGER THROUGH THE DAY TUESDAY. THE FORECAST PROBLEM FOR THIS PART
OF THE FORECAST CONTINUES TO BE HIGH UNCERTAINTY IN TEMPERATURES DUE
TO THE LINGERING WEDGE AND THE WARM FRONT RETREATING NORTHWARD. THE
MODELS HAVE A TENDENCY TO ERODE THE WEDGE TOO QUICKLY...ESPECIALLY
IF THERE IS PRECIPITATION FALLING INTO IT...SO CURRENTLY INDICATE
THE WEDGE STICKING AROUND A BIT LONGER...WITH A LARGE SPREAD IN
TEMPS FROM NW TO SE ACROSS THE AREA TUESDAY AND WEDNESDAY.
CONFIDENCE REMAINS LOW WITH RESPECT TO TEMPS...AS ANY CHANGES TO THE
WEDGE EROSION AND TIMING/POSITION OF THE WARM FRONT AS IT RETREATS
NORTHWARD WILL HIGHLY IMPACT TEMPERATURES. THEY WILL HOWEVER
INCREASE GRADUALLY FROM MIDNIGHT WEDNESDAY THROUGH AROUND MIDNIGHT
THURSDAY AS THE WARM FRONT RETREATS NORTHWARD. SHOULD THE WEDGE BE
LOCKED IN LONGER OR ERODE EARLIER CURRENT FORECAST TEMPS WOULD BE
WAY OFF. TEMPS: LOW 40S NW TO MID 50S SE TUESDAYS...INCREASING TO
LOW 60S NW TO LOW 70S SE ON WEDNESDAY. A NORMAL DIURNAL TEMPERATURE
CURVE SHOULD RETURN WEDNESDAY NIGHT. LOWS IN THE LOW 40S NW TO LOW
50S SE. HIGHS THURSDAY MID 40S NW TO MID 50S SE.

PRECIPITATION: SOME LIGHT RAIN COULD FALL INTO THE WEDGE ON TUESDAY
AS WARM MOIST AIR FROM THE SOUTH ADVECTS IN OVER THE COLD AIR
TRAPPED AT THE SURFACE. THIS WOULD ACT TO THEN LOCK THE WEDGE IN
LONGER. THERE WILL BE A SLIGHT CHANCE TO CHANCE OF PRECIP ACROSS THE
WEST/NORTHWEST PORTIONS OF THE AREA THROUGH WEDNESDAY MORNING...
EVEN THOUGH THE MAIN PRE-FRONTAL CONVECTIVE RAINFALL REMAINS LARGELY
WEST OF THE APPALACHIANS. THE LATEST 12Z ECMWF AND GFS MODEL RUNS
ARE IN BETTER AGREEMENT WITH THE TIMING OF THE FROPA AND THE
ASSOCIATED RAINFALL AS IT MOVES THROUGH THE AREA. THE LATEST RUNS
SUGGEST THAT RAIN WILL BE LIKELY ACROSS THE WEST BEGINNING WEDNESDAY
AFTERNOON...PROGRESSING THROUGH CENTRAL NC WEDNESDAY NIGHT AND
THURSDAY...AND ENDING AROUND MIDNIGHT FRIDAY. THIS IS ANOTHER CASE
OF THE COLD AIR CHASING THE PRECIP...AND FOR NOW EXPECT ALL PRECIP
TO FALL AS RAIN...BUT THAT WILL CONTINUE TO BE MONITORED WITH
SUBSEQUENT FORECAST UPDATES AS THAT PERIOD APPROACHES.

FRIDAY THROUGH SATURDAY: HIGH PRESSURE WILL BUILD IN BEHIND THE
FROPA THURSDAY NIGHT...REMAINING OVER THE REGION INTO THE WEEKEND.
EXPECT A DRY FORECAST PERIOD FOR NOW...WITH HIGHS IN THE LOW TO MID
40S FRIDAY...INCREASING INTO THE 50S SATURDAY. LOWS FRIDAY NIGHT IN
THE 20S.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AS OF 100 AM SUNDAY...

ADVERSE AVIATION CONDITIONS WILL OVERSPREAD CENTRAL NC FROM THE
SOUTH THROUGH 12Z WITH MVFR/IFR CEILINGS AND PATCHES OF LIGHT RAIN
OR LIGHT FREEZING RAIN.

BY 12Z...EXPECT WIDESPREAD LOW END MVFR/IFR CEILINGS ALONG WITH
AREAS OF LIGHT FREEZING RAIN OVER THE PIEDMONT AND SANDHILLS...AND
EITHER LIGHT RAIN OR FREEZING RAIN IN THE COASTAL PLAIN. BETWEEN 12Z-
15Z...THE LIGHT FREEZING RAIN IN THE SANDHILLS AND EASTERN PIEDMONT
SHOULD TRANSITION TO A COLD RAIN. IN ADDITION...A STRENGTHENING LOW
LEVEL JET JUST ABOVE THE SURFACE WILL RESULT IN LOW LEVEL WIND SHEAR
CONDITIONS...ESPECIALLY IN VICINITY OF KRDU...KFAY AND KRWI.

THE FREEZING RAIN IN THE NW PIEDMONT WILL GRADUALLY CHANGE TO A COLD
RAIN BY MID AFTERNOON. ELSEWHERE EXPECT AREAS OF LIGHT RAIN OR
DRIZZLE WITH IFR/LIFR CEILINGS. WHILE THE BULK OF THE RAIN WILL
TAPER OFF BY SUNSET...WIDESPREAD FOG AND DRIZZLE ALONG WITH IFR/LIFR
CEILINGS WILL PERSIST INTO TONIGHT.

MONDAY...A COLD FRONT WILL CROSS THE REGION. WEST-NW FLOW BEHIND THE
BOUNDARY WILL ADVECT A DRIER AIR MASS...LEADING TO A SCOURING OF THE
MURKY NEAR SURFACE AIR MASS. EXPECT IMPROVING AVIATION CONDITIONS
LATE MONDAY THROUGH MONDAY NIGHT. HIGH PRESSURE OVER THE AREA
TUESDAY WILL PROVIDE VFR CONDITIONS. ANOTHER COLD FRONT WILL
APPROACH WEDNESDAY AND CROSS THE REGION WEDNESDAY NIGHT AND
THURSDAY. THIS WEATHER SYSTEM WILL LIKELY CAUSE ANOTHER PERIOD OF
SUB VFR CONDITIONS ACROSS CENTRAL NC.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR NCZ042-077-
078-083>086-088-089.
WINTER WEATHER ADVISORY FROM 4 AM TO NOON EST THIS MORNING FOR
NCZ008>011-024>028-040-041-043-073>076.
WINTER WEATHER ADVISORY FROM 4 AM TO 6 PM EST TODAY FOR
NCZ007-021>023-038-039.

&&

$$
SYNOPSIS...WSS
NEAR TERM...SMITH/HARTFIELD
SHORT TERM...KC
LONG TERM...KC
AVIATION...WSS


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