Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 211458
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1100 AM EDT TUE OCT 21 2014

.SYNOPSIS....A COLD FRONT WILL CROSS CENTRAL NC LATE THIS AFTERNOON
AND THIS EVENING. AN UPPER LEVEL LOW WILL SETTLE SOUTHEAST ACROSS
THE MIDDLE ATLANTIC REGION TONIGHT...AND LINGER OVER THE REGION
THROUGH WEDNESDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1100 AM TUESDAY...

A COLD FRONT CROSSING THE OH AND TN VALLEYS LATE THIS MORNING WILL
CROSS CENTRAL NC LATE THIS AFTERNOON AND TONIGHT. STEADY SW FLOW
AHEAD OF THIS FEATURE ALONG WITH AMPLE SUNSHINE WILL PUSH
TEMPERATURES INTO THE LOW-MID 70S NORTH...AND MID-UPPER 70S SOUTH.

AS THE FRONT GETS CLOSER...MAY SEE AN INCREASE IN
CLOUDINESS...MAINLY ACROSS THE NORTH HALF. WHILE MOISTURE IS LIMITED
(AS PER 12Z GSO SOUNDING)...ENOUGH LIFT GENERATED BY THE FRONT AND
ATTENDANT S/W MAY CAUSE A STRAY SHOWER OR A FEW SPRINKLES ACROSS THE
FAR NORTHERN-NE COUNTIES LATE THIS AFTERNOON THROUGH THIS EVENING.

NW WINDS BEHIND THE FRONT WILL BE BLUSTERY AT TIMES AS LOW LEVEL
COLD AIR ADVECTION COMMENCES. MIN TEMPS MID 40S WEST TO UPEPR 40S
EAST-SE.

&&

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

THE UPPER LOW WILL DRIFT ACROSS THE CHESAPEAKE BAY AND DELMARVA ON
WED...THEN LIFT SLOWLY UP THE MIDDLE ATLANTIC COAST WED NIGHT AND
BEYOND. ASSOCIATED SURFACE COASTAL LOW PRESSURE WILL DEEPEN BY ABOUT
10 MB (FROM JUST UNDER 1010 MB TO JUST UNDER 1000 MB) FROM 12Z WED
TO 12Z THU...AS IT TOO LIFTS UP THE MIDDLE ATLANTIC COAST. THE
COLDEST TEMPERATURES/STEEPEST LAPSE RATES ALOFT ASSOCIATED WITH THE
UPPER LOW...THE FORMER IN EXCESS OF MINUS 20 C AND THE LATTER
BETWEEN 6.5-7 C/KM...WILL CONSEQUENTLY BRUSH THE NORTHEAST PIEDMONT
AND NORTHERN-CENTRAL COASTAL PLAIN...AND RESULT IN A CHANCE OF
"INSTABILITY" SHOWERS OR SPRINKLES WITH DIURNAL HEATING. IT WILL
OTHERWISE BE COOLER AND BREEZY...WITH NORTHWESTERLY DAYTIME WIND
GUSTS UP TO 25 MPH OWING TO THE DEEPENING COASTAL LOW...AND HIGHS IN
THE 60S. CLEARING AND SIMILARLY COOLER WED NIGHT...WITH LOWS MOSTLY
IN THE LOWER TO MIDDLE 40S.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 320 AM TUESDAY...

DEEP NORTHWESTERLY FLOW WILL CONTINUE ON THURSDAY BETWEEN THE UPPER
LOW DRIFTING NORTHEAST ALONG THE NEW ENGLAND COAST AND A SHORTWAVE
RIDGE OVER THE MISSISSIPPI RIVER VALLEY.  LOW-LEVEL THICKNESSES ARE
FORECAST TO BE AROUND 1335M THURSDAY MORNING...AND FULL INSOLATION
DURING THE AFTERNOON SUPPORTS HIGHS IN THE 63-68 RANGE.  THE ALREADY
LOW AMPLITUDE RIDGE WILL BREAK DOWN ON THURSDAY NIGHT INTO FRIDAY AS
ANOTHER WAVE DIVES DOWN THE BACKSIDE OF THE DEPARTING UPPER LOW AND
CROSSES NC FRIDAY NIGHT. WE SHOULD SEE SOME HIGH CLOUDS SPREAD
ACROSS THE AREA LATE THURSDAY NIGHT AND FRIDAY AS AN UPPER JET
STRENGTHENS OVER THE SOUTHEAST AHEAD OF THE TROUGH...THOUGH ITS NOT
CLEAR HOW THICK THE CLOUD COVER WILL BE.  HAVE NUDGED THURSDAY NIGHT
LOWS UP A COUPLE DEGREES INTO THE MID 40S.  HIGHS FRIDAY IN THE
MID/UPPER 60S.

MODELS HAVE TRENDED TOWARD A MUCH MORE COMPACT AND CLOSED OFF WAVE
WITH A STRONG SHOT OF DCVA FRIDAY NIGHT...BUT WITH NO QPF EAST OF
THE MOUNTAINS AS IT ENCOUNTERS A VERY DRY AIRMASS OVER CENTRAL NC.
THE PROGRESSIVE NATURE OF THE TROUGH LOOKS LIKE IT WILL ALSO KEEP A
POTENTIAL (SUB)TROPICAL SYSTEM AND ASSOCIATED MOISTURE IN THE
CARIBBEAN WELL TO OUR SOUTH. THUS THE FORECAST WILL BE DRY THROUGH
THE PERIOD. ONCE THE TROUGH PASSES...THE ECMWF AND GFS ROUGHLY AGREE
THAT UPPER RIDGING WILL BUILD ACROSS THE SOUTHERN US...WITH
THICKNESSES CLIMBING BACK TOWARD 1370M...WHICH IS SLIGHTLY ABOVE
NORMAL.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 745 AM TUESDAY...

A LIGHT SSW SURFACE WIND WILL INCREASE INTO THE 5-10 KT FROM THE WSW
AHEAD OF A COLD FRONT THAT WILL MOVE SOUTHEAST ACROSS THE AREA
BETWEEN 20Z-01Z THIS AFTERNOON AND EVENING. THE PASSAGE OF THE FRONT
WILL CAUSE SURFACE WINDS TO VEER TO WNW AND INCREASE INTO THE 8-14
KT RANGE WITH A FEW GUSTS INTO THE MID-UPPER TEENS KTS. SCATTERED TO
BROKEN CUMULUS WITH BASES BETWEEN 4500-7000 FT AND TOPS BETWEEN 9-15
THOUSAND FT - THE DEEPEST OF WHICH WILL BE CAPABLE OF PRODUCING A
LIGHT SHOWER OR SPRINKLE - WILL ALSO DEVELOP IN THE VICINITY OF THE
PASSING FRONT...WITH THE RELATIVE GREATER CLOUD COVERAGE AND CHANCE
OF A SHOWER AT KRDU AND KRWI. A STEADY WNW TO NW SURFACE WIND...WITH
AN OCCASIONAL GUST INTO THE MID-UPPER TEENS KTS...WILL CONTINUE AS
COLDER AIR MOVES IN BEHIND THE FRONT THIS EVENING.

OUTLOOK: THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC
STATES TONIGHT AND WED WILL RESULT IN PERIODS OF LOW VFR CEILINGS
(BETWEEN 3500-5000 FT) AND A CHANCE OF SHOWERS MAINLY AT KRWI
NORTHEAST TOWARD THE CHESAPEAKE BAY. COASTAL LOW PRESSURE ALONG THE
MIDDLE ATLANTIC AND NORTHEAST COAST WILL PRODUCE NW SURFACE WINDS IN
THE LOW-MID TEENS KTS WITH GUSTS AROUND 20 KTS WED...AND TO A LESSER
DEGREE ON THU.

&&

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

&&

$$

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


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