-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 281734
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1235 PM EST SAT FEB 28 2015

.SYNOPSIS...COLD HIGH PRESSURE WILL EXTEND INTO THE AREA FROM THE
NORTH TODAY. A WEAK DISTURBANCE MOVING SOUTH TO NORTH THROUGH THE
REGION WILL BRING UNSETTLED WEATHER LATE TONIGHT INTO SUNDAY. A COLD
FRONT WILL CROSS THE AREA SUNDAY NIGHT INTO MONDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 1015 AM SATURDAY...

...THREAT FOR A LIGHT ICING EVENT INCREASING FOR THE NC PIEDMONT
EARLY SUNDAY...

REST OF TODAY: HAVE LET THE ADVISORY FOR BLACK ICE EXPIRE ON
SCHEDULE... ALTHOUGH IT MAY TAKE ANOTHER HOUR OR SO FOR SOME AREAS
TO RISE ABOVE FREEZING... AND WILL COVER THIS WITH A SPECIAL WEATHER
STATEMENT. OTHERWISE... MID CLOUDS (AND A FEW LOWER CLOUDS)
STREAMING ACROSS THE NRN/WRN CWA ARE PROJECTED TO OVERSPREAD THE
ENTIRE AREA TODAY... RESULTING IN PARTLY SUNNY TO MOSTLY CLOUDY
SKIES FOR MUCH OF THE DAY... WITH AN EVENTUAL NW-TO-SE PARTIAL
CLEARING TREND LATE IN THE DAY... AS SUGGESTED BY THE NAM AND
CANADIAN MODELS(WHICH ARE DOING BETTER WITH THE CURRENT SKY COVER
WHILE THE GFS IS DEPICTING FAR TOO MANY LOW CLOUDS IN THE TRIAD).
CHILLY SURFACE HIGH PRESSURE CENTERED OVER PA WILL CONTINUE TO
EXTEND SOUTHWARD INTO THE AREA TODAY... AND THIS LOW LEVEL COLD/DRY
AIR ADVECTION COMBINED WITH MORE CLOUDS THAN SUNSHINE WILL HOLD MAX
TEMPS DOWN AT LEAST 2-3 CATEGORIES COOLER THAN YESTERDAY... IN THE
36-43 RANGE. -GIH

TONIGHT AND SUNDAY... LATEST MODEL GUIDANCE HAS TRENDED WETTER LATE
TONIGHT INTO SUNDAY. THIS INCREASES THE THREAT FOR A LIGHT ICING
EPISODE EARLY SUNDAY...MAINLY ACROSS THE PIEDMONT COUNTIES.

TONIGHT...SFC RIDGE AXIS WILL REMAIN OVER THE REGION...MAINTAINING A
SUPPLY OF COLD DRY AIR IN THE LOWEST 2-4K FT OF THE ATMOSPHERE.
ABOVE THE COLD DRY STABLE LAYER...SLY FLOW WILL BE INCREASING IN
RESPONSE TO THE 850MB HIGH DRIFTING OFF THE SE U.S. COAST. THIS
RETURN FLOW WILL ADVECT A WARMER...MORE MOIST AIR MASS INTO THE
CAROLINAS. THIS RETURN FLOW STRENGTHENS SUBSTANTIALLY AFTER 12Z
SUNDAY...THUS EXPECT THE BEST UPGLIDE TO OCCUR AFTER DAYBREAK
SUNDAY. STILL...MODELS HAVE A TENDENCY TO BE A LITTLE TARDY WITH
RETURN FLOW EVENTS. THUS WILL INTRODUCE A SLIGHT/SMALL CHANCE POP
INTO THE FORECAST FOR THE PRE-DAWN HOURS WITH THE HIGHEST POPS
CONFINED TO THE SOUTHERN PIEDMONT/WESTERN SANDHILLS.

PARTIAL THICKNESS TECHNIQUE INDICATES A TREND TOWARD RAIN BY
DAYBREAK SUNDAY AS A DECENT WARM NOSE DEVELOPS ALOFT. HOWEVER MODEL
SOUNDINGS INDICATE A SHALLOW SUB FREEZING LAYER OVER MOST OF CENTRAL
NC AT DAYBREAK SUNDAY. THUS...ANY LIGHT PRECIP THAT OCCURS PRIOR TO
DAYBREAK WILL LIKELY BE IN THE FORM OF FREEZING RAIN/FREEZING
DRIZZLE.

MIN TEMPS WILL VARY FROM THE LOWER 20S IN THE NORTHERN COASTAL PLAIN
WHERE CLOUD COVERAGE WILL INITIALLY BE THINNEST TO THE UPPER 20S
ACROSS THE FAR SOUTH-SW.

SUNDAY...PRECIPITATION EXPECTED TO BECOME MORE COMMON AFTER DAYBREAK
ACROSS THE WEST AS ISENTROPIC UPGLIDE INCREASES. THIS PRECIP FALLING
THROUGH THE DRY AIR MASS IN THE SUB CLOUD LAYER WILL LEAD TO
EVAPORATIVE COOLING...LIKELY LOCKING IN THE SUB FREEZING SFC TEMPS
OVER THE PIEDMONT FOR A GOOD PART OF THE MORNING. DUE TO TIMING
UNCERTAINTY...WILL CAP POPS AT SOLID CHANCE ACROSS THE WESTERN
COUNTIES TRENDING TO SLIGHT CHANCE IN THE COASTAL PLAIN. IF LATER
MODEL RUNS ARE CONSISTENT...AN INCREASE IN POPS WILL BE WARRANTED
AFTER DAYBREAK IN THE WEST.

THE LOCKING IN OF THE SUB FREEZING TEMPS WILL CAUSE A PERIOD OF
LIGHT FREEZING RAIN OVER MOST OF THE PIEDMONT SUNDAY MORNING. AT
THIS TIME NOT EXPECTING ENOUGH ICE ACCRUAL TO CAUSE POWER OUTAGES
BUT COULD SEE SOME SLICK ROADS...ESPECIALLY BRIDGES AND OVERPASSES.
THIS WILL LIKELY WARRANT THE NEED OF AN ADVISORY IN LATER FORECAST
ISSUANCE. IN THE MEANTIME...WILL HIGHLIGHT THREAT IN THE HWO.

EXPECT PRECIPITATION CHANCES TO INCREASE TO LIKELY SUNDAY AFTERNOON
AS UPGLIDE REACHES MAXIMUM. WILL EVENTUALLY SEE FREEZING RAIN
TRANSITION TO A COLD RAIN OVER MOST OF THE PIEDMONT BY MID DAY...AND
OVER THE NW PIEDMONT BY EARLY AFTERNOON. THE OVERCAST SKIES AND
EXPECTED PRECIP WILL LIMIT TEMPS TO THE LOW-MID 30S OVER THE
PIEDMONT COUNTIES TO THE UPPER 30S-LOWER 40S EAST OF HIGHWAY 1.-WSS

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 300 AM SATURDAY...

SUNDAY NIGHT THROUGH MONDAY NIGHT: A WEAK SURFACE LOW ALONG THE
COAST ON SUNDAY EVENING IS EXPECTED TO LIFT NORTHEASTWARD AWAY FROM
THE AREA ON SUNDAY. MEANWHILE... A SURFACE COLD FRONT WILL APPROACH
THE AREA FROM THE WEST ON SUNDAY NIGHT... WITH AN ASSOCIATED SURFACE
LOW MOVING INTO THE EASTERN GREAT LAKES. BOTH THE GFS/NAM SHOW THE
BEST DEEP MOISTURE SHIFTING OFF TO THE EAST OF THE AREA OVERNIGHT...
WITH MID LEVEL DRYING ALOFT NOTED IN BOTH THE GFS AND NAM BUFR
SOUNDINGS. THUS... WITH A LACK OF A GOOD COLD AIR SOURCE TO THE
NORTH AND DRYING ALOFT TAKING PLACE... EXPECT WE SHOULD SEE TEMPS
SLOWLY WARM OVERNIGHT... RESULTING IN LOW TEMPS OCCURRING DURING THE
SUNDAY EVENING TIME FRAME OF THE OVERNIGHT PERIOD. EXPECT LOWS WILL
GENERALLY BE IN THE MID TO UPPER 30S... WITH PERHAPS A FEW LOCATIONS
ACROSS THE FAR SOUTHEAST NEAR 40 DEGREES.

THE AFOREMENTIONED SURFACE COLD FRONT TO IS EXPECTED TO MOVE THROUGH
THE AREA LATE MORNING INTO THE AFTERNOON... AND GENERALLY DRY. HOW
FAR THE CAD BOUNDARY ERODES BEFORE THE FRONT DROPS
SOUTH/SOUTHEASTWARD THROUGH THE AREA IS STILL IN QUESTION... WITH
SOME LOCATIONS IN THE HEART OF THE CAD ACROSS THE NORTHWEST PIEDMONT
SEEING HIGH TEMPS OCCUR AFTER THE FROPA AS THE CAD AIRMASS WOULD
THEN BE SCOURED OUT (WITH POSSIBLY EVEN SOME SUN). THINK STATISTICAL
GUIDANCE IS TOO HIGH FOR MONDAY... AND WENT CLOSER TO THE RAW
GFS/NAM MODEL VALUES. THIS YIELDS HIGH TEMPS RANGING FROM THE UPPER
40S/NEAR 50 NORTH TO THE UPPER 50S/NEAR 60 SOUTH. SURFACE HIGH
PRESSURE WILL BUILD INTO THE AREA FROM THE NORTH AND NORTHWEST ON
MONDAY NIGHT USHERING IN ANOTHER DRY COLD SURFACE AIRMASS. LOWS BY
TUESDAY MORNING AREA EXPECTED TO BE IN THE UPPER 20S NORTH TO THE
MID TO MAYBE UPPER 30S SOUTH.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 320 AM SATURDAY...

TUESDAY THROUGH FRIDAY: A 1030+ MB SURFACE
HIGH... EXPECTED TO BE LOCATED ALONG THE SOUTHERN MID ATLANTIC COAST
ON TUESDAY MORNING... WILL QUICKLY SHIFT EASTWARD AND OFFSHORE BY
TUESDAY AFTERNOON... LEAVING A DRY SURFACE AIRMASS IN ITS WAKE.
MEANWHILE... MID LEVEL RIDGING WILL BUILD ACROSS THE AREA AS THE MID
LEVEL FLOW ACROSS THE CONUS BECOMES MORE AMPLIFIED... A SURFACE LOW
IS EXPECTED TO DEVELOP/STRENGTHEN INVOF THE FOUR CORNERS REGION
MONDAY NIGHT... WILL THEN QUICKLY LIFT EAST-NORTHEASTWARD AND INTO
THE GREAT LAKES REGION BY TUESDAY EVENING... WITH ADDITIONAL ENERGY
DIVING DOWN THE BACK SIDE OF THE ASSOCIATED MID/UPPER LEVEL
TROUGH... AS THE FRONT BECOMING PARALLE WITH THE MID TO UPPER LEVEL
FLOW BY TUESDAY NIGHT AND QUITE WET... WITH THE MID LEVEL RIDGE OVER
OUR REGION TO START THE PERIOD SHIFTING EASTWARD.

SOUTHERLY FLOW IN ADVANCE OF THE FRONT ACROSS CENTRAL NC WILL
QUICKLY INCREASE ON TUESDAY ATOP THE COLD SURFACE AIRMASS... WITH
LIKELY AN INSITU CAD WEDGE DEVELOPING AS SOME LIGHT ISENTROPICALLY
DRIVEN PRECIP IS EXPECTED TO BEGIN SPREADING ACROSS CENTRAL NC BY
TUESDAY AFTERNOON INTO THE EVENING. HOWEVER... WITH SURFACE HIGH
LONG GONE BY TUESDAY EVENING AND SOUTHERLY FLOW INCREASING WE SHOULD
SEE THE CAD WEDGE BEGIN TO RETREAT OVERNIGHT TUESDAY... WITH TEMPS
LIKELY RISING OVERNIGHT. THE AFOREMENTIONED SURFACE COLD FRONT IS
EXPECTED TO SLOWLY SHIFT EASTWARD AND INTO AND ACROSS THE MOUNTAINS
ON WEDNESDAY... WITH THE FRONT NOW EXPECTED TO MOVE THROUGH OUR AREA
ON WEDNESDAY NIGHT INTO THURSDAY MORNING (THE GFS AND ECMWF ARE NOW
WITHIN ABOUT 6 HOURS OF EACH OTHER NOW... WITH THE GFS ON THE FASTER
SIDE)... WITH WPC FAVORING THE SLOWER ECMWF TIMING ACROSS OUR AREA.
THE MAIN SHOWER ACTIVITY (WHICH COULD BRING HEAVY RAIN AT TIMES..
ESPECIALLY ACROSS THE NORTHWEST PIEDMONT) IS EXPECTED TO GENERALLY
BE ALONG AND BEHIND THE FRONT. THE GFS HINTS AT THE POTENTIAL FOR
SOME SWITCH OVER TO LIGHT SNOW BEFORE PRECIP ENDS ON THURSDAY
EVENING... BUT THIS IS WAY TOO FAR OUT IN TIME TO ADD ANY NON-
LIQUID... WHICH WOULD PROBABLY RESULT IN LITTLE TO NO IMPACT AS
WELL. COLD AIR CHASING THE PRECIP. DRY WEATHER IS EXPECTED TO
SPREAD BACK INTO THE AREA BY FRIDAY.

TEMPS DURING THE MEDIUM RANGE WILL BE A ROLLER COASTER... WITH HIGHS
TEMPS... TUESDAY... 40S TO LOWER 50S... WEDNESDAY 60S AND 70S...
THURSDAY 40S AND 50S... AND FINALLY FRIDAY BACK IN THE 40S (WITH
MAYBE SOME 30S EVEN). LOWS WILL FOLLOW A SIMILAR PATTERN. HOWEVER...
ALL PRECIP AS OF NOW APPEARS TO BE IN THE FORM OF LIQUID FOR THE
MEDIUM RANGE.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
AS OF 1235 PM SATURDAY...

PRIMARY AVIATION CONCERNS NEXT 24 HRS: CIGS DROPPING TO MVFR AND IFR
STARTING LATE THIS EVENING (SOUTH) INTO THE EARLY OVERNIGHT HOURS
(NORTH)... WITH POTENTIAL LOW LEVEL WIND SHEAR DEVELOPING.

SURFACE HIGH PRESSURE CENTERED TO OUR NORTH NEAR BALTIMORE WILL
CONTINUE TO NOSE SOUTHWARD INTO CENTRAL/WRN NC THROUGH THIS EVENING.
EXPECT NO MORE THAN A DECK OF VFR MID CLOUDINESS THROUGH THE 03Z
(FAY) TO 06Z (RDU/RWI) TIME FRAME... WITH VFR VSBYS. A DEVELOPING
INVERTED TROUGH NEAR THE COAST COMBINED WITH A SURGE OF MOISTURE
FROM NRN FL SPREADING NORTHWARD INTO WRN/CNTRL NC OVERNIGHT WILL
BRING A GROWING RISK OF PRECIP LATE... SPREADING IN FROM SOUTH TO
NORTH... WITH LIGHT PRECIP AFFECTING FAY FIRST THEN MOVING INTO
INT/GSO/RDU AREAS LATE TONIGHT. RWI MAY NOT SEE MUCH IF ANY PRECIP
UNTIL NEAR 18Z SUNDAY OR LATER. CIGS WILL LOWER TO MVFR THEN RAPIDLY
TO IFR LATE TONIGHT INTO EARLY SUN MORNING... WITH A GOOD CHANCE OF
LOW LEVEL WIND SHEAR ESPECIALLY AT FAY STARTING AS EARLY AS 09Z.
CONFIDENCE IS HIGH IN IFR OR LIFR CIGS AFTER 10Z-12Z SUNDAY.
FREEZING RAIN IS THE MOST LIKELY PRECIP TYPE AT INT/GSO LATE TONIGHT
THROUGH SUNDAY... WITH FREEZING RAIN CHANGING TO RAIN AT RDU... AND
BRIEF FREEZING RAIN CHANGING EARLY TO RAIN AT FAY. GLAZING OF ICE IS
MOST LIKELY AT INT/GSO... LESS SO AT RDU/FAY.

LOOKING BEYOND 18Z SUNDAY... IFR/LIFR CONDITIONS WILL HOLD THROUGH
THE REST OF SUNDAY WITH PRECIP SPREADING ENE INTO RWI. EVEN IF LLWS
CRITERIA ARE NOT STRICTLY MET... WINDS AT ALL SITES WILL BE
INCREASING WITH HEIGHT FROM THE SW THROUGH THE LOWEST 2-3 KFT...
MAKING HANDLING OF SOME AIRCRAFT CHALLENGING. PRECIP ENDS EARLY
SUNDAY EVENING BUT LIFR CLOUDS EXPECTED TO LINGER THROUGH SUNDAY
NIGHT... THEN ERODE FROM THE TOP MONDAY AS A COLD FRONT SWEEPS
THROUGH FROM NW TO SE. HIGH PRESSURE BUILDS IN FROM THE NORTH LATE
MON THROUGH MON NIGHT... THEN ANOTHER APPROACHING STORM SYSTEM WILL
BRING A GOOD CHANCE OF SUB-VFR CIGS EARLY TUE THROUGH TUE NIGHT. MAY
SEE A BREAK TO MVFR OR VFR CIGS WED... BUT YET ANOTHER STORM SYSTEM
IS POISED TO BRING INCREASING WINDS WED THEN MORE SUB-VFR CONDITIONS
AND PRECIP WED NIGHT/THU. -GIH
-- End Changed Discussion --

&&

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

&&

$$

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