Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 210740
AFDRAH

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

.SYNOPSIS....A LEAD SHORTWAVE TROUGH ALOFT WILL CROSS OUR REGION
THIS MORNING...FOLLOWED BY THE PASSAGE OF A COLD FRONT THIS
AFTERNOON AND EVENING. AN UPPER LEVEL LOW WILL SETTLE SOUTHEAST
ACROSS THE MIDDLE ATLANTIC REGION TONIGHT THROUGH WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM TUESDAY...

A LEAD SHORTWAVE TROUGH ALOFT AND ASSOCIATED MID LEVEL (AOA 9-10
THOUSAND FT) CLOUD BAND AND VIRGA - OR ISOLATED SPRINKLE AT THE
SURFACE - WILL MOVE EAST ACROSS CENTRAL NC THROUGH 12Z. SKIES WILL
CONSEQUENTLY BECOME MOSTLY CLEAR FROM WEST TO EAST THROUGH MID-
MORNING...WHICH WILL PROVIDE AN OPPORTUNITY TO SEE THE ORIONID
METEOR SHOWER IN THE COUPLE HOURS PRIOR TO DAYBREAK OVER THE
PIEDMONT COUNTIES.

ANOTHER STRONG NORTHERN STREAM SHORTWAVE TROUGH WILL AMPLIFY SHARPLY
SSE FROM NORTHERN MI AT 07Z TO THE CENTRAL APPALACHIANS BY THIS
EVENING...THEN ULTIMATELY CULMINATE IN THE DEVELOPMENT OF AN UPPER
LOW OVER THE MIDDLE ATLANTIC REGION BY EARLY WED. A PRECEDING
SURFACE COLD FRONT...ANALYZED FROM WESTERN NY TO NORTHERN AR AT
07Z...WILL MOVE EAST ACROSS CENTRAL NC THIS AFTERNOON AND EVENING.
WITH MOSTLY SUNNY SKIES PRECEDING THE FRONT...AND A WEST TO NW
DOWNSLOPE WIND AHEAD AND BEHIND IT...TEMPERATURES WILL CLIMB INTO
THE LOWER 70S OVER THE WESTERN PIEDMONT TO UPPER 70S OVER EASTERN
SANDHILLS AND SOUTHERN COASTAL PLAIN.

THOUGH MOISTURE AND INSTABILITY ARE FORECAST TO REMAIN LIMITED
OVERALL...THE FORMER CONFINED TO A THIN LAYER BETWEEN 850-750 MB AND
THE LATTER AOB 150 J/KG PER BUFR SOUNDINGS AND SREF PROBABILITIES...
LOW LEVEL CONVERGENCE ALONG THE FRONT AMIDST FALLING HEIGHTS ALOFT
LATE IN THE DAY MAY SUPPORT A BAND OF WIDELY SCATTERED SHOWERS OR
SPRINKLES MAINLY ACROSS THE NORTHERN PIEDMONT AND NORTHERN COASTAL
PLAIN...WHERE VERY WEAK INSTABILITY AND DEEPER LIFT SHOULD BE
RELATIVELY MAXIMIZED IN CLOSEST PROXIMITY TO THE AMPLIFYING
SHORTWAVE TROUGH AND ASSOCIATED COLD POOL ALOFT.  ANY SCATTERED
SHOWERS SHOULD MOVE EAST AND/OR DISSIPATE WITH THE ONSET OF
NOCTURNAL COOLING AND THE PASSAGE OF THE COLD FRONT BY EVENING.

TONIGHT: THE CENTER OF THE STRONGEST MID LEVEL HEIGHT FALLS...ON THE
ORDER OF 100 M/12 HR...WILL CROSS THE NORTHEAST HALF OF THE CWFA AS
THE POTENT SHORTWAVE TROUGH CONTINUES TO AMPLIFY SSE OVERNIGHT. THIS
FORCING FOR ASCENT IN CONJUNCTION WITH THE ARRIVAL OF THE COLD
POOL/STEEPENING LAPSE RATES ALOFT WILL SUPPORT A RENEWED CHANCE OF
SPRINKLES OR LIGH RAIN SHOWERS OVER THE NORTHEAST PIEDMONT AND
NORTHERN COASTAL PLAIN. DRY AND VARIABLY CLOUDY ELSEWHERE. LOWS
MOSTLY 45 TO 50 DEGREES.

&&

.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 /00Z TUESDAY THROUGH SATURDAY/...
AS OF 210 AM TUESDAY...

AN UPPER LEVEL TROUGH AND ASSOCIATED MID LEVEL CLOUD BAND AND VIRGA -
OR ISOLATED SPRINKLES AT THE SURFACE - WILL MOVE EAST ACROSS CENTRAL
NC THROUGH 10Z. OTHERWISE...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 9-13 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 FROM KRDU AND
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...MWS
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...BLS
AVIATION...MWS


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