Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 171143
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
745 AM EDT WED SEP 17 2014

.SYNOPSIS...COOL HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM THE
NORTH TODAY AND PERSIST THROUGH THE REMAINDER OF THE WORK WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 340 AM WEDNESDAY...

TODAY...SURFACE COLD FRONT CURRENTLY DRIFTING SOUTH ACROSS CENTRAL
NC (AT 07Z FRONT WAS FAIRLY ALIGNED WITH HIGHWAY 64) AND SHOULD BE
DRAPED ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN THIS
MORNING...DRIFTING INTO NORTHERN SC-SE NC THIS AFTERNOON. A MID-
UPPER LEVEL VORTICITY MAXIMUM CROSSING SC EARLY THIS MORNING WILL
MAINTAIN A THREAT FOR SHOWERS AND AN ISOLATED STORM FOR THE FAR
SOUTHERN SECTIONS OF OUR FORECAST AREA THROUGH 12Z.

LATER THIS MORNING...THE COOL MOIST STABLE AIR MASS BEHIND THE FRONT
SHOULD RESULT IN A WEAK DAMMING EVENT. AS IS TYPICAL WITH THIS SET-
UP...SHOULD SEE WIDESPREAD LOW CLOUDS AND PATCHES OF LIGHT RAIN OR
DRIZZLE AS A SERIES OF UPPER LEVEL DISTURBANCES PASS OVERHEAD. THE
EXTENSIVE CLOUDS AND SPOTTY LIGHT PRECIP SHOULD HOLD TEMPS IN THE
LOW-MID 70S ACROSS THE PIEDMONT. GFS APPEARS TOO OPTIMISTIC IN ITS
DEPICTION OF SCATTERING THE LOW CLOUDS INTO A SCATTER-BROKEN
STRATOCU DECK THIS AFTERNOON. IF THE GFS IS MORE CORRECT...THEN
EXPECT SCATTERED SHOWERS RATHER THAN LIGHT RAIN ACROSS THE PIEDMONT
ALONG WITH WARMER TEMPS. CURRENTLY...PLAN TO HAVE MAX TEMPS RANGE
FROM THE LOWER 70S NW TO THE LOWER 80S FAR SOUTH-SE.

SLIGHT TO MODERATE INSTABILITY ACROSS THE SANDHILLS AND SOUTHERN
COASTAL PLAIN SUGGEST A THREAT FOR SCATTERED CONVECTION THIS
AFTERNOON. GFS DEPICTS BULK SHEAR OF 30KTS...SUGGESTING SOME
ORGANIZATION TO THE CONVECTION...MAINLY IN THE FORM OF A BROKEN
LINE. MAY SEE A STRONG WIND GUSTS WITH CELLS THAT HAVE SUSTAINED
UPDRAFTS DUE TO PRECIP LOADING BUT MAJORITY OF SHOWERS AND STORMS
WILL BE BELOW SEVERE LIMITS. FORCING THAT NOT ALL THAT IMPRESSIVE SO
PLAN TO CAP POPS AT 30-40 PERCENT.

TONIGHT...EXPECT WEAK CAD AIR MASS TO PERSIST OVER MOST OF THE
PIEDMONT WITH PATCHES OF DRIZZLE OR FOG AND LOW CLOUDS. BULK OF
CONVECTION IN THE SE WILL DIMINISH WITH LOSS OF HEATING AND LACK OF
SUPPORT ALOFT. MAY SEE A SLIGHT UPSURGE IN LIGHT PRECIP TOWARD
MORNING AS MOST OF THE MODELS DEPICT A MINOR S/W APPROACHING FROM
THE WEST. MIN TEMPS GENERALLY 60-65.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 340 AM WEDNESDAY...

THURSDAY...MINOR S/W PROJECTED TO PASS ACROSS THE FORECAST AREA IN
THE MORNING. WEAK SUBSIDENCE IN ITS WAKE IN THE AFTERNOON AND
ADVECTION OF DRIER AIR WILL BEGIN EROSION OF RESIDUAL CAD AIR MASS
IN THE PIEDMONT. HOWEVER...MODELS TYPICALLY ARE TOO AGGRESSIVE WITH
THIS TRANSITION. FAVOR A SLOWER IMPROVEMENT TREND THAN ADVERTISED BY
THE MODELS. THIS LEADS TO MAX TEMPS ON THE COOL SIDE OF GUIDANCE. IF
EROSION IS EVEN SLOWER THAN EXPECTED...MAX TEMPS MAY BE AS MUCH A 3-
4 DEGREES TOO WARM IN THE PIEDMONT. CONVECTION THURSDAY AFTERNOON
APPEARS LIMITED TO THE FAR EAST-SE SECTIONS. JUST WEAK INSTABILITY
AND SHEAR PROJECTED SO EXPECT MAINLY ISOLATED SHOWERS IN THE
COASTAL PLAIN/SANDHILLS. MAX TEMPS MID-UPPER 70S NORTH TO AROUND 80
SOUTH.

THURSDAY NIGHT...EXPECT GRADUAL IMPROVEMENT IN SKY CONDITIONS. THIS
MAY LEAD TO SOME PATCHY FOG BUT INTRUSION OF DRIER AIR NEAR THE
SURFACE MAY LIMIT/INHIBIT FOG FORMATION. BEST CHANCE FOR FOG WILL
LIKELY BE THE SE HALF. MIN TEMPS IN THE UPPER 50S NW TO THE LOWER
60S SE.
&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 340 AM WEDNESDAY...

A PORTION OF THE LONGWAVE TROUGH INITIALLY ALONG THE EAST COAST WILL
BE LEFT BEHIND...OFFSHORE THE SE US COAST THIS WKND...BUT THE
OTHERWISE DEAMPLIFYING/LIFTING TROUGH WILL YIELD TO RISING HEIGHTS
ALOFT OVER THE CAROLINAS...AS A FLAT MID LEVEL RIDGE RIDGE NOSES
EASTWARD FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY. THE RE-
ESTABLISHMENT AND AMPLIFICATION OF A WESTERN NOAM RIDGE WILL THEN
RESULT IN DOWNSTREAM TROUGH AMPLIFICATION FROM SOUTH-CENTRAL CANADA
TO THE EAST-CENTRAL US DAYS 5-7.

BENEATH THE RISING HEIGHTS ALOFT...A CANADIAN-SOURCE SFC HIGH (AROUND
1030 MB) WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES
AND RIDGE SOUTH/SOUTHWESTWARD THROUGH THE EASTERN STATES THROUGH THE
FIRST HALF OF THE WEEKEND...BEFORE YIELDING - AMIDST FALLING HEIGHTS
DOWNSTREAM OF THE AFOREMENTIONED REDEVELOPING TROUGH ALOFT HEADED
FOR THE EAST-CENTRAL US - TO APPALACHIAN-LEE SFC TROUGH DEVELOPMENT
SUN...AND A PASSING COLD FRONT MON-MON NIGHT.

THOUGH THE CANADIAN RIDGING WILL RESULT IN A RELATIVELY PROLONGED
PERIOD OF EAST TO NORTHEAST LOW LEVEL FLOW THROUGH EARLY THIS
WEEKEND...THE LATEST GUIDANCE SUGGESTS THE BRUNT OF THE ASSOCIATED
COOLER AND DRIER AIR WILL HOLD OVER THE NORTHERN MIDDLE ATLANTIC AND
NORTHEAST STATES. IN ADDITION...THE ORIENTATION OF THE LOW LEVEL
RIDGE AXIS SHOULD ALSO DIRECT MARITIME MOISTURE/CLOUDS AROUND THE
RIDGE...TO THE SOUTH OF CENTRAL NC. AS SUCH...SKIES ARE APT TO BE
PARTLY TO MOSTLY SUNNY OVER CENTRAL NC...WITH TEMPERATURES ABOUT A
CATEGORY WARMER THAN EARLIER ANTICIPATED...IN THE MIDDLE 70S TO
AROUND 80 DEGREES FRI-SAT. WARMER YET AHEAD OF THE APPROACHING FRONT
SUN-MON - LIKELY LOWER TO PERHAPS MIDDLE 80S...WITH JUST A SLIGHT
CHANCE OF SHOWERS ATTENDING THE FRONT LATE MON...GIVEN A LIMITED
GULF MOISTURE FEED. COOLER TUE...AND THOUGH THERE REMAINS SOME
POTENTIAL FOR LINGERING LIGHT RAIN (ESPECIALLY EAST) PER THE 12Z
EC...THE 00Z EC HAS TRENDED TOWARD THE MORE CONSISTENT AND FAVORED
EC ENSEMBLE MEAN WITH A "CLEANER" FRONTAL PASSAGE AND DRIER SOLUTION
FOR TUE.
&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 745 AM WEDNESDAY...

LOW LEVEL NORTH-NORTHEAST FLOW BEHIND A DEPARTING SURFACE COLD FRONT
WILL MAINTAIN A COOL MOIST STABLE AIR MASS. THIS WILL RESULT IN
WIDESPREAD IFR/MVFR CEILINGS ACROSS MUCH OF THE PIEDMONT INCLUDING
KINT/KGSO AND KRDU. PATCHES OF LIGHT RAIN OR DRIZZLE MAY DEVELOP
THIS MORNING. NEAR KFAY...A BRIEF PERIOD OF MVFR CEILINGS THIS
MORNING WILL LIFT INTO THE HIGH END MVFR-LOW END VFR CEILINGS BY
AFTERNOON WITH A THREAT FOR SCATTERED SHOWERS. THE SHOWER THREAT
WILL BE GREATER TO THE SOUTH AND EAST OF KFAY.

THE ADVERSE AVIATION WEATHER CONDITIONS WILL PERSIST ACROSS MUCH OF
CENTRAL NC TONIGHT INTO THURSDAY MORNING DUE TO LOW CEILINGS. A
GRADUAL IMPROVEMENT IN AVIATION CONDITIONS EXPECTED BY THURSDAY
AFTERNOON AS DRIER AIR BEGINS TO ARRIVE INTO THE LOWER LEVELS OF THE
ATMOSPHERE.

A PERIOD OF MVFR/IFR VISIBILITY DUE TO FOG MAY OCCUR THURSDAY NIGHT
INTO EARLY FRIDAY. OTHERWISE...VFR CONDITIONS ARE EXPECTED TO OCCUR
THROUGH SUNDAY AS HIGH PRESSURE GAINS GREATER INFLUENCE ON OUR
WEATHER.

&&

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

&&

$$

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...MWS
AVIATION...WSS



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