Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 272002
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
255 PM EST SAT DEC 27 2014

.SYNOPSIS...HIGH PRESSURE NEAR THE CAROLINA COAST THIS AFTERNOON
WILL MOVE OFFSHORE TONIGHT. A COLD FRONT WILL APPROACH THE REGION
FROM THE NORTHWEST ON SUNDAY... AND GRADUALLY MOVE THROUGH THE
REGION ON MONDAY. HIGH PRESSURE WILL BUILD INTO THE SOUTHEAST
FOR THE MIDDLE TO END OF THE WORK WEEK.
&&

.NEAR TERM /TONIGHT THROUGH SUNDAY/...
AS OF 255 PM SATURDAY..

LATEST SURFACE ANALYSIS SHOWS AN AREA OF SURFACE HIGH PRESSURE
CENTERED NEAR THE NC/SC COAST ALONG THE COASTAL CAROLINAS AND
VIRGINIA. A POSITIVELY TILTED DEAMPLIFYING UPPER TROUGH ACROSS THE
WESTERN PLAINS AT MIDDAY TODAY WILL CONTINUE TO SHIFT SLOWLY EAST
TODAY AND TONIGHT. THE NORTHERN PORTION OF THE TROUGH ASSOCIATED
WITH THE NORTHERN JET STREAM WILL SHEAR EAST INTO THE EASTERN GREAT
LAKES WHILE BY LATE SUNDAY AFTERNOON. THE SOUTHERN EXTENT OF THE
TROUGH IS SHARPER AND MOVES SLOWLY EAST REACHING THE ARKLATEX BY
SUNDAY EVENING. THE ASSOCIATED COLD FRONT WHICH EXTENDS FROM
MICHIGAN SOUTHWEST TO EASTERN TX AT MIDDAY TODAY WILL MOVE EAST
REACHING EASTERN PA AND NORTHWEST GA BY LATE SUNDAY AFTERNOON.

MAINLY CLEAR SKIES ACROSS CENTRAL NC THIS AFTERNOON WILL GIVE WAY TO
INCREASING HIGH AND MID CLOUDINESS THIS EVENING AS MOISTURE BEGINS
TO INCREASE AHEAD OF THE FRONT. WHILE HIGH AND MID LEVEL CLOUDINESS
WILL THICKEN OVERNIGHT... NAM/GFS/SREF BUFR SOUNDINGS ALL NOTE THAT
THE LOWER THIRD OF THE TROPOSPHERE IS SLOW TO MOISTEN OVERNIGHT
UNTIL LOW LEVEL MOISTURE SURGES INTO THE REGION FROM THE SOUTHWEST
TOWARD DAYBREAK SUNDAY. THE PRECIPITATION IS LARGELY DRIVEN BY
ISENTROPIC LIFT AROUND THE 295K SURFACE WITH THE BEST SURGE OF LIFT
SKIRTING ACROSS THE NORTHWESTERN EDGE OF CENTRAL NC AND WILL
ADVERTISE LOW CATEGORICAL POPS THERE. FORCING FOR ASCENT DECREASES
TO THE SOUTH AND EAST ON SUNDAY WITH LOW CHANCE POPS ADVERTISED FOR
THE SANDHILLS AND SOUTHERN COASTAL PLAIN. SO SUNDAY WILL FEATURE
CLOUDY SKIES ACROSS CENTRAL NC IT WONT BE WASHOUT FOR EVERYONE.
MAINLY SPOTTY LIGHT RAIN IS EXPECTED TO THE SOUTH AND SOUTHEAST OF
RALEIGH WITH THE MOST WIDESPREAD RAIN EXPECTED NEAR AND ESPECIALLY
TO THE NORTHWEST OF INTERSTATE 85.

TEMPERATURES WILL BE A LITTLE TRICKY AS THEY WILL TEND TO FALL
QUICKLY THIS EVENING AFTER SUNSET BUT THE OVERNIGHT TREND WILL BE
COMPLICATED BY THE INCREASING MID AND HIGH CLOUDS AND THE LIGHT
SOUTHERLY STIRRING AHEAD OF THE APPROACHING COLD FRONT. WILL
FORECAST LOWS IN THE MID 40S WEST TO LOWER 40S EAST. HIGHS ON SUNDAY
WILL BE COMPLICATED BY TE PRECIPITATION WHICH SHOULD KEEP HIGHS IN
THE MID 50S ACROSS THE NORTHWEST PIEDMONT WITH MID 60S ACROSS THE
SANDHILLS AND SOUTHERN COASTAL PLAIN WHERE THE RAIN WILL BE MORE
SCATTERED. -BLAES
&&

.SHORT TERM /SUNDAY NIGHT/...
AS OF 345 AM SATURDAY...

WARM ADVECTION DRIVEN PRECIP...OUT AHEAD OF THE UPPER TROUGH AND
COLD FRONT MOVING INTO THE OHIO/TENNESSEE VALLEYS SUNDAY MORNING...
WILL BE PRIMARILY FOCUSED OVER THE NORTHWEST PIEDMONT.  THIS INITIAL
SURGE OF WARM ADVECTION IS FORECAST TO WEAKEN WITH TIME AND
NORTHWARD EXTENT..WITH LIGHT QPF AMOUNTS OF A TENTH OF AN INCH OR
LESS FOR MOST LOCATIONS. TO THE EAST...WHERE LIFT IS WEAKER AND
MOISTURE IS LIMITED...ONLY A FEW HUNDREDTHS ARE EXPECTED.  HAVE
ADJUSTED POPS TO SHOW A GREATER RANGE FROM HIGH END LIKELY INT HE
NORTHWEST TO LOW END CHANCE IN THE SOUTHEAST. BY SUNDAY
AFTERNOON...TEMP ADVECTION BECOMES NEARLY NEUTRAL WITH NO SIGNS OF
ANY APPRECIABLE WAVES IN THE DEEP SOUTHWESTERLY FLOW.  THUS...EXPECT
A LULL IN PRECIP THROUGH SUNDAY LATE AFTERNOON/EVENING...BEFORE THE
COLD FRONT SINKS SOUTH INTO NC SUNDAY NIGHT AND MORE WIDESPREAD RAIN
SPREADS BACK IN FROM THE SOUTHWEST BY MONDAY MORNING IN RESPONSE TO
A 180KT UPPER JET OVER THE OHIO VALLEY AND STRENGTHENING ISENTROPIC
LIFT.

THE RESULTING HIGHS SUNDAY AFTERNOON WILL EXHIBIT A GREATER RANGE OF
VALUES...WITH MID 50S IN THE NORTHWEST TO MID 60S POSSIBLE IN THE
SOUTHEAST. LOWS SUNDAY NIGHT IN THE MID 40S NORTH TO LOWER 50S SOUTH.


&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
AS OF 325 AM SATURDAY...

MON AND MON NIGHT: THE MODELS ARE IN GOOD AGREEMENT ALOFT REGARDING
THE AMPLIFICATION OF A SHORTWAVE TROUGH ACROSS NORTHERN MEXICO
THROUGH TONIGHT... FOLLOWED BY A DEAMPLIFICATION OF THE TROUGH TO
THE MIDDLE ATLANTIC STATES BY EARLY MON. THE INTENSIFICATION AND
MIGRATION OF AN ASSOCIATED 160-180 KT UPPER JET ACROSS THE OH VALLEY
AND NORTHEAST WILL PLACE CENTRAL NC BENEATH THE RIGHT ENTRANCE
REGION OF THE JET...WHICH WILL CAUSE THE LOW LEVEL FLOW /ABOVE THE
SHALLOW POST-FRONTAL DAMMING HIGH/ TO ACCELERATE AND ASSUME A MORE
SOUTHERLY COMPONENT. STRENGTHENING ISENTROPIC LIFT WILL
RESULT...WHICH WILL CAUSE LIGHT RAIN TO OVERSPREAD CENTRAL NC LATE
SUNDAY NIGHT THROUGH EARLY MON AFTERNOON...BEFORE TAPERING TO
OCCASIONAL DRIZZLE OR BARELY MEASURABLE LIGHT RAIN...AS AN
ASSOCIATED SERIES OF WEAK FRONTAL WAVES TRACK OFF THE COAST OF THE
CAROLINAS...THROUGH MON NIGHT.

THE COMBINATION OF BOTH CAA AND DIABATIC/EVAPORATIVE COOLING WILL
LIKELY RESULT IN SLOWLY FALLING TEMPERATURES ACROSS THE NORTHERN
CWFA --INTO THE 40S-- THROUGHOUT THE DAY...WHILE THE SOUTHERN TIER
WILL HAVE AN OPPORTUNITY TO WARM INTO THE 60S DURING THE MIDDAY
HOURS BEFORE ALSO COOLING DURING THE AFTERNOON HOURS. LOWS...WITH
CONTINUED LOW OVERCAST AND THE AFOREMENTIONED OCCASIONAL DRIZZLE OR
VERY LIGHT RAIN...IN THE UPPER 30S TO LOWER 40S.

TUE: A SECONDARY SHORTWAVE TROUGH...ANOTHER DEAMPLIFYING ONE IN WSW
FLOW ALOFT...IS FORECAST TO CROSS THE CENTRAL APPALACHIANS EARLY
TUE. THE PASSAGE OF THIS FEATURE AND ASSOCIATED WEAK HEIGHT FALLS
ALOFT AND LIFT WILL MAINTAIN A SUFFICIENTLY SATURATED LOWEST SEVERAL
THOUSAND FT TO WARRANT A CONTINUED SLIGHT CHANCE OF LIGHT RAIN OR
(MORE LIKELY) DRIZZLE INTO EARLY TUE...BEFORE NW 925-850 MB FLOW
BEHIND THE PASSING SHORTWAVE PROMOTES BOTH DOWNSLOPE FLOW AND A
DISSIPATION OF THE CAD INVERSION VIA CAA - BOTH MECHANISMS THAT
SHOULD SERVE TO SCOUR THE CAD REGIME AND PROMOTE STEADY CLEARING.
WITH A FEW HOURS OF AFTERNOON SUNSHINE PROBABLE...LONGEST OVER THE
NW PIEDMONT...TEMPERATURES SHOULD RESPOND TO NEAR NORMAL.

TUE NIGHT-FRI: STRONG...ARCTIC HIGH PRESSURE OVER THE ROCKIES EARLY
IN THE PERIOD WILL OTHERWISE SPRAWL EAST ACROSS THE MIDDLE ATLANTIC
AND SOUTHEAST STATES...THROUGH THU...BENEATH GENERALLY WESTERLY FLOW
BETWEEN CONFLUENT BRANCHES OF THE UPPER JET...BEFORE DRIFTING
OFFSHORE AHEAD OF AN EJECTING DESERT SW (BRIEFLY) CUTOFF LOW FRI-
SAT. THE RESULT WILL BE COOL CONDITIONS --MOST NOTABLY WED AND THU
MORNINGS WHEN TEMPERATURES SHOULD DIP WELL INTO THE 20S GIVEN
PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1290-1300 METER RANGE--
WITH A PERIOD OF PASSING MID-HIGH CLOUDS DURING THE DAY
WED...BETWEEN OTHERWISE MOSTLY CLEAR.

MEDIUM RANGE GUIDANCE (NOT SURPRISINGLY) DIVERGES WITH RESPECT TO
THE EJECTION OF THE AFOREMENTIONED DESERT SW LOW...SO FORECAST
DETAILS ARE MORE UNCERTAIN FOR FRI...THOUGH CLOUDINESS AND RAIN
CHANCES WILL CERTAINLY BE ON THE RISE THROUGH THE START OF NEXT
WEEKEND.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
AS OF 1250 PM SATURDAY...

...HIGH CONFIDENCE OF VFR CONDITIONS THROUGH MIDNIGHT TONIGHT WITH
ADVERSE AVIATION CONDITIONS SPREADING INTO MUCH OF CENTRAL NC EARLY
SUNDAY... VFR CONDITIONS ARE EXPECTED ACROSS CENTRAL NC THIS
AFTERNOON AND EVENING AS HIGH AND MID LEVEL CLOUDINESS INCREASES
LATE. AN AREA OF SHOWERS ACROSS UPSTATE GA/SC WILL MOVE INTO WESTERN
NC VERY LATE THIS AFTERNOON BUT THIS PRECIPITATION SHOULD LARGELY
DISSIPATE. IF SOMEHOW IT MAKES IT INTO THE WESTERN PIEDMONT IT WOULD
OCCUR AS A VFR RAIN SHOWER WITH A HIGH CEILING AND LIMITED
VISIBILITY REDUCTION.

MORE SIGNIFICANT WEATHER ARRIVES WELL AFTER MIDNIGHT AS DEEPER
MOISTURE IS DRAWN INTO CENTRAL NC AHEAD OF AN APPROACHING COLD
FRONT. RAIN WILL SPREAD INTO THE WESTERN PIEDMONT FROM THE SOUTHWEST
BETWEEN 10-14Z INCLUDING THE KINT AND KGSO TERMINALS AND THEN MOVE
EAST ARRIVING AROUND 13-17Z AT KRDU AND KRWI WITH SEVERAL HOURS OF
RAIN EXPECTED IN THE TRIAD. SPOTTIER RAIN IS EXPECTED NEAR KFAY
OCCURRING FROM 15-22Z. THE BEST SUPPORT FOR PRECIPITATION WILL OCCUR
ACROSS NORTHWESTERN NC WITH THE AMOUNT...DURATION AND LIKELIHOOD OF
PRECIPITATION DECREASING TOWARD THE SOUTHEAST. IN THE TRIAD CEILINGS
SHOULD FALL INTO THE IFR TO POSSIBLY LIFR RANGE AFTER PRECIPITATION
BEGINS WITH VSBYS IN THE MVR/IFR RANGE...CONDITIONS ESPECIALLY CIGS
WILL LIKELY BE A LITTLE BETTER BUT STILL REDUCED TO THE EAST AT KRDU
AND KRWI AND SHOULD BE BETTER FURTHER SOUTH AND EAST AT KFAY. LIGHT
SOUTH-SOUTHWEST WINDS AT 190-250 DEG AT LESS THAN 10KTS WILL
CONTINUE THROUGH THE 24 HOUR TAF PERIOD.

LOOKING AHEAD...THE AREA OF PRECIPITATION ON SUNDAY SHOULD MOVE OUT
OF THE AREA BY SUNSET BEFORE ANOTHER AREA OF RAIN ASSOCIATED WITH
THE COLD FRONT AND A SURFACE WAVE MOVES ACROSS THE AREA LATE SUNDAY
NIGHT AND MONDAY. LINGERING LOW CLOUDS AND DRIZZLE WILL CONTINUE
MONDAY NIGHT INTO TUESDAY BEFORE CONDITIONS IMPROVE LATER TUESDAY
WITH FAIR WEATHER EXPECTED ON WEDNESDAY. -BLAES
&&

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

&&

$$

SYNOPSIS...BLAES
NEAR TERM...BLAES
SHORT TERM....BLS
LONG TERM...MWS
AVIATION...BLAES


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