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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 030309
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1000 PM EST MON MAR 2 2015

.SYNOPSIS...HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH
TONIGHT AND WILL SHIFT OFFSHORE DURING THE DAY TUESDAY AS A LOW
PRESSURE SYSTEM TRACKS NORTHEAST FROM THE CENTRAL PLAINS INTO THE
GREAT LAKES.

&&

.NEAR TERM /TONIGHT THROUGH TUESDAY NIGHT/...
-- Changed Discussion --
AS OF 1000 PM MONDAY...

AFTER A PLEASANTLY WARM DAY...COOLER AND DRIER AIR IS WORKING ITS
WAY INTO THE AREA FROM THE NORTH-NORTHEAST AS A 1034MB SURFACE HIGH
TRANSLATES EAST ACROSS THE MID-ATLANTIC STATES.  THE PRIMARY COLD
FRONT IS TO OUR SOUTH...BUT THERE APPEARS TO BE A SECONDARY
BOUNDARY...WITH NOTICEABLY HIGH DEWPOINTS POOLING ALONG IT...MOVING
FROM THE COASTAL PLAIN TOWARD THE PIEDMONT.  THIS COMPLICATES THE
OVERNIGHT FORECAST AS THE DRIER...SUB-20F DEWPOINT AIR  OVER THE THE
NORTHWEST PIEDMONT TRIES TO PUSH SOUTH BUT MAY ULTIMATELY BE HALTED
OR SHUNTED OFF TO THE WEST.  MOST MODEL ARENT HANDLING THIS VERY
WELL...EVIDENT IN PART BY THE MUCH DRIER THAN FORECAST BOUNDARY
LAYER ON THE 00Z KGSO RAOB...SO WILL LEAN ON THE RAP/HRRR WHICH HAS
DEWPOINTS MOSTLY IN THE 20S TO LOWER 30S TUESDAY MORNING.  TEMPS
WILL CONTINUE TO FALL INTO THE 30S OVERNIGHT...BUT AS SOME 290K
ISENTROPIC LIFT AND  HIGHER BASED STRATUS SPREAD NORTH AND
EAST ACROSS THE AREA...TEMPS SHOULD STABILIZE MOSTLY ABOVE FREEZING.

THE BIGGEST FORECAST ISSUES TONIGHT WILL STILL BE 1) WHETHER OR NOT
ANY LIGHT RAIN/DRIZZLE SPREADS FAR ENOUGH NORTH AND EAST INTO THE
SUB-FREEZING AIRMASS BEFORE A WEAK DIURNAL RECOVERY IN TEMPS BEGINS
ON TUESDAY MORNING...OR 2) PRECIP IS EVEN HEAVY ENOUGH WETBULB TEMPS
BELOW FREEZING IN AREAS WHERE THEY ARE INITIALLY ABOVE FREEZING.
18Z AND 00Z GUIDANCE CONTINUES TO ONLY SHOW A COUPLE HUNDREDTHS AT
BEST AND MOSTLY COMING AFTER 12Z.  THE RAP AND HRRR ARE COMPLETELY
DRY THROUGH 12Z.  WILL LOWER POPS A LITTLE AND JUST MAINTAIN A
MENTION JUST FREEZING DRIZZLE IN THE SMALL AREA WHERE TEMPS  AT AT
OR BELOW 32...WHICH IS CONFINED TO JUST THE NORTH PIEDMONT PRIOR TO
15Z.  NO ADVISORY FOR FREEZING RAIN IS NEEDED AT THIS TIME.  TEMPS ON
TUESDAY WILL MOVE LITTLE OFF MORNING LOWS...MID 30S TO LOWER 40S.

A WARM FRONT IS EXPECTED TO LIFT NORTHWARD TOWARD CENTRAL NC TUE
NIGHT...WITH TEMPERATURES RISING OVERNIGHT ACROSS MUCH OF THE
AREA...ALTHOUGH THEY COULD REMAIN NEAR STEADY IN THE N/NW PIEDMONT.
LIGHT RAIN/DRIZZLE COULD TAPER AS THE WARM FRONT LIFTS WITH
EXPANDING FOG CONDITIONS POSSIBLE.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AS OF 300 PM MONDAY...

THE FORECAST PROBLEM FOR THIS PART OF THE FORECAST CONTINUES TO BE
THE UNCERTAINTY IN TEMPERATURES DUE TO THE POTENTIALLY LINGERING
WEDGE AND THE TIMING AND EXTENT TO WHICH THE WARM FRONT RETREATS
NORTHWARD. GIVEN THAT THE MODELS HAVE A TENDENCY TO ERODE THE WEDGE
TOO QUICKLY...ESPECIALLY IF THERE IS PRECIPITATION FALLING INTO
IT...CURRENTLY FORECAST THE WEDGE STICKING AROUND INTO WEDNESDAY
AFTERNOON IN THE FAR NW PIEDMONT...WITH A LARGE SPREAD IN TEMPS FROM
NW TO SE ACROSS THE AREA. CONFIDENCE REMAINS SOMEWHAT LOW WITH
RESPECT TO TEMPS...AS ANY CHANGES TO THE TIMING AND POSITION OF THE
WEDGE/WARM FRONT AS THEY ERODE/RETREAT NORTHWARD WILL HIGHLY IMPACT
TEMPERATURES. THEY WILL HOWEVER INCREASE GRADUALLY THROUGH AROUND
MIDNIGHT THURSDAY BEFORE THE COLD FRONT BEGINS MOVING INTO THE NW.
KEEPING IN MIND THE POTENTIAL MARGIN FOR ERRORS...FORECAST HIGH
TEMPS IN THE MID 60S NW TO MID 70S SE ON WEDNESDAY. A NORMAL DIURNAL
TEMPERATURE CURVE SHOULD RETURN WEDNESDAY NIGHT...ALTHOUGH THE
TEMPERATURE GRADIENT WILL BE QUITE LARGE AND WILL DEPEND ON THE
TIMING AND POSITION OF THE COLD FRONT...EXPECT LOWS IN THE UPPER 30S
NORTH TO LOW 50S SOUTH WEDNESDAY NIGHT AND HIGHS IN THE LOW 40S
NORTH TO MID 50S SOUTH ON THURSDAY AND DECREASING BEHIND THE FRONT.

PRECIPITATION: THERE WILL BE A SLIGHT CHANCE OF PRECIP...MAINLY
ACROSS THE WESTERN PORTIONS OF THE AREA WEDNESDAY...EVEN THOUGH THE
MAIN PRE-FRONTAL CONVECTIVE RAINFALL REMAINS LARGELY ALONG OR WEST
OF THE APPALACHIANS UNTIL WEDNESDAY AFT/EVE. SOUTHWESTERLY WINDS
WILL BE QUITE STRONG ON WEDNESDAY AFT/EVE AS THE GRADIENT TIGHTENS
AHEAD OF THE FRONT. LATE WEDNESDAY AFTERNOON IS STARTING TO SHAPE UP
AS A HIGH SHEAR/LOW CAPE EVENT. FORECAST SOUNDINGS INDICATE 200-300
JOULES OF CAPE AND 0-3 KM SHEAR VALUES AROUND 35 KTS...MAINLY ALONG
AND EAST OF I-95 AT THIS TIME. WITH SURFACE TEMPS EXPECTED IN THE
MID 70S AND DEWPOINTS AROUND 60 DEGREES...THUNDERSTORMS WILL BE
POSSIBLE WEDNESDAY AFTERNOON...THUS WILL INTRODUCE A SLIGHT CHANCE
ACROSS THE EAST WITH THIS AFTERNOON`S FORECAST. 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 WEDNESDAY NIGHT...
PROGRESSING NW TO SE THROUGH CENTRAL NC THROUGH MIDNIGHT FRIDAY.
THIS REMAINS CASE OF THE COLD AIR CHASING THE PRECIP...BUT FOR NOW
STILL EXPECT ALL PRECIP TO FALL AS RAIN...HOWEVER THERE IS A SMALL
CHANCE THAT A FEW SNOWFLAKES COULD MIX IN ON THE TAIL END OF THE
EVENT.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 300 PM MONDAY...

FRIDAY THROUGH SATURDAY: HIGH PRESSURE WILL BUILD IN BEHIND THE
FRONT THURSDAY NIGHT...REMAINING OVER THE REGION INTO THE WEEKEND.
EXPECT A DRY FORECAST FRIDAY THROUGH SATURDAY...WITH HIGHS IN THE
UPPER 30S TO LOW 40S FRIDAY...INCREASING THROUGH THE WEEKEND AND
INTO THE UPPER 50S TO LOW 60S BY MONDAY. LOWS WILL SEE A SIMILAR
TREND...INCREASING FROM MAINLY LOW 20S LOW 20S THU AND FRI NIGHTS TO
THE LOW TO MID 30S BY SAT AND SUN NIGHTS. THERE IS SOME MODEL
DISAGREEMENT TOWARD THE END OF THE PERIOD WITH REGARD TO PRECIP
CHANCES...AS THE ECMWF BRINGS PRECIP IN FROM THE SOUTHWEST SUNDAY
NIGHT AND THE GFS IS COMPLETELY DRY. WILL FORECAST A SLIGHT CHANCE
FOR RAIN SUN NIGHT/MONDAY...ALTHOUGH CONFIDENCE IS LOW AT THIS TIME.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
AS OF 745 PM MONDAY...

STRONG (1032 MB) BUT TRANSIENT MODIFIED ARCTIC HIGH PRESSURE WILL
RIDGE SOUTH INTO NC TONIGHT...THEN BUILD QUICKLY OFFSHORE ON TUE.
INITIALLY VFR CONDITIONS THIS EVENING WILL BE THREATENED WITH FIRST
A NARROW BAND OF LOW MVFR CLOUDS THAT NEAR TERM GUIDANCE WILL
DEVELOP IN THE VICINITY OF KRWI IN THE NEXT COUPLE OF HOURS...THEN
SWEEP...IN NORTHEASTERLY FLOW...TO THE SOUTHWEST ACROSS THE
REMAINDER OF CENTRAL NC BETWEEN 02-07Z...LASTING AT ANY ONE LOCATION
FOR JUST 2-3 HOURS BEFORE DEPARTING.

MEANWHILE...AN AREA OF 4-5 THOUSAND FT CEILINGS OVER SC WILL EXPAND
NORTH AS THE FLOW IN THAT LAYER STRENGTHENS AND CAUSES AIR TO GENTLY
RISE ATOP THE AFOREMENTIONED RIDGE OF SURFACE HIGH PRESSURE AND
ASSOCIATED NORTHEASTERLY FLOW BENEATH. CONFIDENCE IS RELATIVELY HIGH
THAT CEILINGS WITHIN THIS AREA OF CLOUDS WILL THEN GRADUALLY LOWER
TO INTO MVFR RANGE FROM WSW TO ENE ON TUE - FIRST AT KINT/KGSO AND
LAST AT KRWI. THERE IS A LESSER...MEDIUM CHANCE (AROUND 50
PERCENT)... THAT CONDITIONS WILL LOWER TO IFR...WITH ACCOMPANYING
PERIODS OF LIGHT RAIN/DRIZZLE MAINLY AT KGSO/KINT...AND PERHAPS AS
FAR EAST AS KRDU...TUE MORNING. IF PRECIPITATION WERE TO INDEED
OCCUR... TEMPERATURES WILL BE CLOSE TO FREEZING AT KINT/KGSO...WHERE
AN ASSOCIATED PERIOD OF FREEZING PRECIPITATION WOULD BE POSSIBLE.

OUTLOOK: TUE NIGHT: SUB-VFR CONDITIONS WILL CONTINUE TO DEVELOP
NORTHEAST AND LOWER ACROSS CENTRAL NC THROUGH TUE NIGHT...SUCH THAT
LIFR CONDITIONS WITH RESPECT TO CEILINGS AND POSSIBLY VISIBILITIES
IN DENSE FOG...ARE EXPECTED TO PREVAIL LATE TUE NIGHT-WED
MORNING...IN ASSOCIATION WITH THE SLOW RETREAT/APPROACH OF A WARM
FRONT FROM THE SOUTHEAST.

WED-THU: A RETURN TO VFR WILL BE PROBABLE WITH THE PASSAGE OF THE
WARM FRONT LATER WED AT KFAY/KRWI/KRDU...BUT THIS IMPROVEMENT WILL
BE DELAYED...OR MAY NOT OCCUR AT ALL AT KINT/KGSO...BEFORE A COLD
FRONT AND AREA OF RAIN ARRIVE FROM THE NORTHWEST WED NIGHT...AND
PERSIST THROUGH MUCH OF THU.

&&

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

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...CBL/BLS
SHORT TERM...KC
LONG TERM...KC
AVIATION...RAH