Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 011754
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
155 PM EDT WED OCT 01 2014

.SYNOPSIS...WEAK HIGH PRESSURE WILL EXTEND SOUTHWARD INTO THE REGION
THROUGH THURSDAY. A COLD FRONT WILL APPROACH THE MOUNTAINS FROM THE
WEST ON FRIDAY... THEN SWEEP EAST ACROSS THE REGION FRIDAY NIGHT AND
EARLY SATURDAY. COOL HIGH PRESSURE WILL FOLLOW THE FRONT FOR THE
WEEKEND.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1200 PM WEDNESDAY...

OVERVIEW: AN UPPER LEVEL LOW CENTERED ALONG THE MID-ATLANTIC COAST
WILL SHIFT OFFSHORE TONIGHT AS A SHORTWAVE RIDGE OVER THE TN/OH
VALLEY BUILDS EAST TOWARD THE SOUTHERN APPALACHIANS. SMALL AMPLITUDE
WAVES DIGGING SOUTHEASTWARD THROUGH VA ON THE WESTERN PERIPHERY OF
THE EXITING UPPER LOW COULD PROVIDE GLANCING BOUTS OF DPVA ACROSS
FAR NORTHERN NC TODAY...THOUGH SYNOPTIC SUBSIDENCE WILL GRADUALLY
OVERSPREAD THE REGION FROM THE WEST THIS EVENING INTO TONIGHT AS THE
SHORTWAVE RIDGE PROGRESSES INTO THE SOUTHERN APPALACHIANS AND WEAK
SFC HIGH PRESSURE WILL CONTINUE TO EXTEND SOUTHWARD INTO CENTRAL NC.

TEMPS: DENSE FOG EARLIER THIS MORNING HAS LIFTED INTO LOW STRATUS
ACROSS THE NORTHERN/NW PIEDMONT...THOUGH CEILINGS HAVE YET TO SHOW
SIGNS OF MIXING OUT AND ACTUALLY APPEAR TO BE THICKENING ALONG THE I-
85 CORRIDOR...WHERE THE ADVECTION OF A SHALLOW COOL/MOIST AIRMASS
SOUTHWESTWARD FROM VA INTO THE N/NW PIEDMONT HAS APPARENTLY OFFSET
BUOYANT MIXING ASSOC/W INCREASING INSOLATION. ALTHOUGH LOW CEILINGS
MAY PERSIST LONGER THAN ANTICIPATED (PERHAPS UNTIL 18-19Z)...THE
COMBINATION OF INCREASING SUN ANGLE AND VEERING LOW-LEVEL FLOW
SHOULD ALLOW CLEARING BY MID TO LATE AFTERNOON AT LATEST. WILL
INDICATE SLIGHTLY COOLER HIGHS IN THE UPPER 70S ACROSS THE FAR N/NW
PIEDMONT...WITH HIGHS IN THE LOWER 80S (80-83F) ELSEWHERE.

PRECIP: THE LATEST NAM CONTINUES TO DEVELOP LIGHT PRECIP OVER THE
NORTHERN PIEDMONT TONIGHT...THOUGH THE LATEST GFS GUIDANCE IS DRY.
IT IS DIFFICULT TO ASCERTAIN WHY THE NAM CONTINUES TO DEVELOP
PRECIPITATION TONIGHT GIVEN VERY WEAK LOW-LEVEL FLOW (LITTLE OR NO
ADVECTION)...MARGINAL/SHALLOW MOISTURE...AND A THOROUGHLY DRY
AIRMASS ABOVE 700 MB AS SYNOPTIC SUBSIDENCE INCREASES FROM THE WEST.
AT THIS TIME...WILL CONTINUE TO INDICATE A DRY FCST THROUGH
TONIGHT...THOUGH THERE MUST BE A PHYSICAL REASON THE NAM IS
GENERATING PRECIP...SUBTLE AS IT MAY BE...AND A SLIGHT CHANCE OF
SHOWERS MAY NEED TO BE INTRODUCED ACROSS THE N/NW PIEDMONT TONIGHT
IN SUBSEQUENT FORECASTS. -VINCENT

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 1200 PM WEDNESDAY...

THE SHORTWAVE RIDGE WILL CONTINUE TO PROGRESS EAST ON THU...
BECOMING CENTERED DIRECTLY OVER THE CAROLINAS AND VA THU AFTERNOON
INTO THU NIGHT. IN THE LOWER LEVELS...WEAK SFC HIGH PRESSURE
EXTENDING SOUTHWARD INTO CENTRAL NC WILL SHIFT EASTWARD IN ADVANCE
OF THE RIDGE ALOFT...EVENTUALLY MOVING OFFSHORE THE CAROLINA COAST
FRI MORNING AS A STRONG COLD FRONT RAPIDLY ADVANCES ACROSS THE MS
RIVER INTO THE OH/TN VALLEY. GIVEN A THOROUGHLY DRY/STABLE H7-H3
LAYER ATOP SHALLOW/MARGINAL DIURNAL INSTABILITY (AT BEST) IN THE
ABSENCE OF ANY SIGNIFICANT LOW OR UPPER LEVEL FORCING...WILL
CONTINUE TO INDICATE A DRY FORECAST. EXPECT HIGHS SIMILAR TO
TODAY...IN THE UPPER 70S TO LOWER 80S...COOLEST WHERE FOG AND LOW
STRATUS PERSIST THE LONGEST PRIOR TO MIXING OUT. LOWS THU NIGHT
SIMILAR TO PREVIOUS NIGHTS ALBEIT SLIGHTLY WARMER WITH THE ONSET OF
A LIGHT SOUTHERLY RETURN FLOW IN THE WEST BY SUNRISE...IN THE LOWER
60S. -VINCENT

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
AS OF 155 PM WEDNESDAY...

FRIDAY INTO EARLY SATURDAY...

THE TIMING OF THE MAIN COLD FRONT ALONG WITH POTENTIAL CONVECTIVE
OUTFLOW BOUNDARIES WILL BE THE MAIN CONCERNS FRIDAY AFTERNOON AND
FRIDAY NIGHT. THEY WILL BE THE DRIVING MECHANISMS FOR SHOWERS AND
SCATTERED THUNDERSTORMS. AS IT CURRENTLY APPEARS... THE MAIN THREAT
OF CONVECTION SHOULD HOLD OFF UNTIL LATE IN THE AFTERNOON IN THE
WEST... AND UNTIL THE EVENING IN THE CENTRAL AND EAST. SOME MODELS
SUGGEST THAT THE FAYETTEVILLE TO GOLDSBORO AREAS MAY NOT SEE THE
CHANCE OF SHOWERS/THUNDER UNTIL LATE EVENING AND OVERNIGHT.

THERE CONTINUES TO BE QUITE A SPREAD IN THE MODELS WITH THE DETAILS
OF TIMING AND QPF ASSOCIATED WITH THE FRONT... EVEN THOUGH THEY ARE
TRENDING TOWARD THE AFOREMENTIONED SOLUTION. FOR NOW... FRIDAY
APPEARS THAT IT WILL BE PARTLY SUNNY AND WARM WITH HIGHS IN THE
LOWER 80S... EXCEPT 75-80 IN THE NORTHWEST PIEDMONT. POP WILL
INCREASE FROM WEST TO EAST DURING THE LATE AFTERNOON INTO THE
EVENING WITH THE TIME FRAME OF 400 PM THROUGH MIDNIGHT HIGHEST POP
IN THE WEST... AND 800 PM THROUGH 400 AM HIGHEST IN THE CENTRAL AND
EAST. A LEAD CONVECTIVE LINE MAY RIDE OUT AHEAD OF THE FRONT ALONG
ASSOCIATED OUTFLOW BOUNDARIES... FOLLOWED BY CONVECTION ALONG THE
FRONT ITSELF. QPF APPEARS TO BE ON THE ORDER OF 0.25 TO 0.50 IN THE
WESTERN PIEDMONT... WITH AVERAGE AMOUNTS AROUND 0.25 IN THE SE (DUE
TO WEAKENING OF THE CONVECTION DUE TO OVERNIGHT TIMING IN THE
EASTERN ZONES).

THE SEVERE THREAT APPEARS MINIMAL WITH ONLY MODEST INSTABILITY AND
WEAK SHEAR EXPECTED. ALSO... TIMING OF THE CONVECTION FRIDAY NIGHT
IN THE EAST WILL BE LATER INTO THE NOCTURNAL CYCLE... THUS THE
WEAKENING TREND EXPECTED.

BY 12Z/SAT...

THERE MAY STILL BE A LINGERING CHANCE OF SHOWERS IN THE EAST... BUT
SKIES WILL BE CLEARING FROM THE NW. THIS CLEARING TREND ALONG WITH
INCREASING CAA THROUGH THE DAY WILL LEAD TO A NOTICEABLE NW BREEZE AT
10-20 MPH. IT WILL BE MUCH COOLER WITH HIGHS IN THE UPPER 60S TO MID
70S NW TO SE.

SATURDAY NIGHT THROUGH WEDNESDAY...

A STRONG AND COOL HIGH PRESSURE WILL BRING OUR FIRST REAL REFRESHING
AIR MASS OF THE 2014 FALL SEASON SAT NIGHT INTO MONDAY. WITH MOSTLY
CLEAR SKIES... LOWS WILL DIP INTO THE 40S FOR MOST OF THE REGION.
HIGHS SHOULD ONLY BE IN THE MID 60S TO LOWER 70S SUN-MON.

A MODERATING TREND IN TEMPERATURES IS EXPECTED TUE-WED ALONG WITH
DRY CONDITIONS AS THE HIGH PRESSURE SLOWLY DRIFTS TO OUR SE THEN.
LOWS WILL RETURN TO THE 50S WITH HIGHS 73-78 (NEAR NORMAL).

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 1200 PM WEDNESDAY...

24-HR TAF PERIOD: SUB-VFR CEILINGS HAVE LARGELY MIXED OUT ACROSS
CENTRAL NC AS OF 15Z...EXCEPT AT THE INT/GSO TERMINALS WHERE
IFR/LIFR CEILINGS MAY PERSIST UNTIL 18-19Z BEFORE MIXING OUT DUE TO
THE ADVECTION OF A SHALLOW COOL/MOIST UPSTREAM AIRMASS BY A LIGHT
NORTHEAST LOW-LEVEL FLOW. EVEN AT THE INT/GSO TERMINALS...VFR
CONDITIONS SHOULD PREVAIL THIS AFTERNOON/EVENING AS SUN ANGLE
INCREASES AND LOW-LEVEL FLOW VEERS TOWARD THE SOUTH. BASED ON
PERSISTENCE...FOG/LOW CEILINGS ARE EXPECTED TO DEVELOP AGAIN LATE
TONIGHT...08-12Z THURSDAY...WITH CONDITIONS IMPROVING BY LATE THU
MORNING.

LOOKING AHEAD: ASIDE FROM A CONTINUED POTENTIAL FOR MORNING FOG/
STRATUS ON FRIDAY...VFR CONDITIONS WILL OTHERWISE PREVAIL.
WIDESPREAD ADVERSE AVIATION CONDITIONS ARE EXPECTED FRIDAY NIGHT AS
A STRONG COLD FRONT CROSSES THE CAROLINAS FROM THE WEST...
ACCOMPANIED BY WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS. VFR
CONDITIONS WILL PREVAIL IN THE WAKE OF THE FRONT THIS WEEKEND AS
HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST. -VINCENT

&&

$$

SYNOPSIS...V/PWB
NEAR TERM...V
SHORT TERM...V
LONG TERM...PWB
AVIATION...V



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