Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 011850
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
250 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 CAROLINAS FRIDAY NIGHT.
COOL HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST OVER THE
WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 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 INTO THE SOUTHERN APPALACHIANS. MEANWHILE...A
SOUTHERN STREAM SHORTWAVE CENTERED OVER NORTHERN AL/GA AT 18Z THIS
AFTERNOON WILL TRACK EAST THROUGH UPSTATE SC AND FAR S/SE PORTIONS
OF NC TONIGHT.

TEMPS: THE ADVECTION OF A SHALLOW COOL/MOIST AIRMASS SOUTHWESTWARD
FROM VA INTO THE N/NW PIEDMONT ACTED TO OFFSET THE EFFECTS OF
INSOLATION (AND RESULTANT BUOYANT MIXING) THIS MORNING...ALLOWING
LOW CEILINGS TO PERSIST LONGER THAN PREVIOUSLY ANTICIPATED. THIS
`ADVECTIVE OFFSET` WILL DECREASE IN EFFICIENCY AS LOW-LEVEL FLOW
VEERS TO THE EAST/SOUTH DURING PEAK HEATING...AND A CLEARING TREND
SHOULD BE NOTICEABLE SHORTLY (IF NOT ALREADY) IN THE N/W PIEDMONT
WHERE HIGHS WILL REACH THE MID/UPPER 70S...WITH HIGHS ELSEWHERE IN
THE UPPER 70S TO LOWER 80S. LOWS TONIGHT SIMILAR TO PREVIOUS NIGHTS
GIVEN LITTLE AIRMASS CHANGE...IN THE UPPER 50S TO LOWER 60S.

PRECIP: THE 12Z NAM GUIDANCE CONTINUES TO DEVELOP LIGHT PRECIP OVER
CENTRAL NC TONIGHT...BETWEEN 00-06Z OR 03-09Z. IN COMPARISON TO THE
LATEST MESOANALYSIS DATA...IT APPEARS THAT THE NAM IS TOO GENEROUS
W/REGARD TO THE DEGREE OF LOW-LEVEL MOISTENING OCCURRING IN
ASSOCIATION WITH THE DEVELOPMENT OF A VERY WEAK RETURN FLOW OVER THE
CAROLINAS THIS AFTERNOON/EVENING. AS SUCH...MARGINAL NOCTURNAL
DESTABILIZATION DEPICTED BY THE NAM IN THE SFC-H8 OR SFC-H7 LAYER
TONIGHT IS LIKELY OVERDONE. EVEN IF SHALLOW INSTABILITY IS PRESENT
AS THE NAM SUGGESTS...DIURNAL TIMING WOULD BE POOR...VIRTUALLY NO
LOW-LEVEL FOCUS OR FORCING MECHANISM WILL BE PRESENT...AND THE
INCREASINGLY DRY/SUBSIDENT MID-LEVEL AIRMASS OVERSPREADING THE
REGION FROM THE WEST WOULD RESULT IN AN EQUILIBRIUM LEVEL ~10
KFT...FURTHER DECREASING (THOUGH NOT NEGATING) THE POTENTIAL THAT
RELATIVELY DIFFUSE DPVA ASSOCIATED WITH THE SOUTHERN STREAM
SHORTWAVE WILL BE SUFFICIENT TO INITIATE...SUSTAIN...OR MAINTAIN
SUCH SHALLOW CONVECTION. WITH ALL OF THE ABOVE IN MIND...WILL
CONTINUE TO INDICATE A DRY FORECAST THROUGH TONIGHT. -VINCENT

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 245 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 130 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...VINCENT
NEAR TERM...VINCENT
SHORT TERM...VINCENT
LONG TERM...PWB
AVIATION...VINCENT


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