Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 201057
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
657 AM EDT MON OCT 20 2014

.SYNOPSIS....HIGH PRESSURE CENTERED OVER NC THIS MORNING WILL MOVE
OFFSHORE TODAY. A LEAD SHORTWAVE TROUGH ALOFT WILL CROSS OUR REGION
TONIGHT...FOLLOWED BY A STRONGER ONE - AND PRECEDING SURFACE COLD
FRONT - THAT WILL SETTLE ACROSS THE MIDDLE ATLANTIC STATES LATE TUE
AND TUE NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 325 AM MONDAY...

A DEAMPLIFYING SOUTHERN STREAM MID-UPPER DISTURBANCE OVER WESTERN
TN...AND PRECEDING AREA OF CIRRUS AT 07Z...WILL CONTINUE ENE ACROSS
NC/VA THROUGH NOON. SURFACE HIGH PRESSURE CENTERED DIRECTLY OVER
CENTRAL NC THIS MORNING WILL MOVE OFFSHORE TODAY...AS A STRONGER
NORTHERN STREAM SHORTWAVE TROUGH AND ASSOCIATED AREA OF MAXIMUM
HEIGHT FALLS ALOFT (~60 M/12 HR) AMPLIFY ACROSS THE UPPER MIDWEST
AND LOWER OH VALLEY. CIRRUS ASSOCIATED WITH THE NORTHERN STREAM WAVE
WILL FOLLOW QUICKLY ON THE DEPARTING HEELS OF THE ONES FROM SOUTHERN
STREAM...WHILE THE LOW LEVEL RETURN FLOW ALSO PROMOTES THE ONSHORE
DEVELOPMENT/ADVECTION OF AN AREA OF STRATOCUMULUS MAINLY OVER THE
COASTAL PLAIN AND EASTERN PIEDMONT/SANDHILLS. TEMPERATURES WILL ALSO
MODERATE IN RETURN/WARMING SW FLOW...INTO THE UPPER 60S TO LOWER
70S.

TONIGHT: THE SHORTWAVE TROUGH FORECAST TO AMPLIFY FROM THE UPPER
MIDWEST THIS MORNING TO THE LEE OF THE CENTRAL APPALACHIANS
OVERNIGHT...WILL CAUSE A MID LEVEL CLOUD BAND AND ASSOCIATED VIRGA
OR ISOLATED SPRINKLES TO MOVE EAST ACROSS CENTRAL NC BETWEEN 06-12Z.
A DRY SUB-CLOUD LAYER/BELOW 10 THOUSAND FT SHOULD PRECLUDE THE
OCCURRENCE OF ANY MEASURABLE PRECIPITATION. NOT AS COOL...WITH
LOWS IN THE UPPER 40S TO LOWER 50S.

&&

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

ANOTHER STRONG NORTHERN STREAM SHORTWAVE TROUGH...ONE LOCATED OVER
ONTARIO THIS MORNING...WILL AMPLIFY SHARPLY SSE ACROSS THE OH VALLEY
TUE AND CENTRAL APPALACHIANS TUE NIGHT...CULMINATING IN THE
DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC REGION BY EARLY
WED. A SURFACE COLD FRONT PRECEDING THE AMPLIFYING SHORTWAVE TROUGH
WILL CROSS CENTRAL NC TUE AFTERNOON...BUT NOT BEFORE TEMPERATURES
CLIMB INTO THE LOWER TO MIDDLE 70S. THOUGH MOISTURE AND INSTABILITY
IS FORECAST TO REMAIN WEAK OVERALL...THE FORMER CONFINED TO A THIN
LAYER BETWEEN 850-750 MB AND THE LATTER AOB 200 J/KG PER BUFR
SOUNDINGS...LOW LEVEL CONVERGENCE ALONG THE FRONT AMIDST THE RENEWED
HEIGHT FALLS ALOFT MAY SUPPORT A BAND OF WIDELY SCATTERED SHOWERS
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...BUT
WITH A LATE NIGHT RENEWED CHANCE (20-30 PERCENT) OF SHOWERS AGAIN
OVER THE NORTHEAST PORTION OF THE CWFA...AS THE STRONGEST HEIGHT
FALLS/COOLING TEMPERATURES ALOFT...AND MID-UPPER LEVEL DIVERGENCE
AND DEFORMATION OVERSPREAD NE NC AND SE VA. DRY ELSEWHERE...BUT WITH
PARTLY TO MOSTLY CLOUDY CONDITIONS OWING TO THE STEEP LAPSE RATES
AND CYCLONIC FLOW ALOFT. LOWS MOSTLY 45 TO 50 DEGREES.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 335 AM MONDAY...

A STRONG SHORTWAVE DIVING THROUGH THE UPPER TROUGH OVER THE EASTERN
US...AND CROSSING NC TUESDAY NIGHT...WILL CLOSE OFF INTO AN UPPER
LOW OFF THE DELMARVA ON WEDNESDAY.  BENEATH THE UPPER LOW...STEEP
TROPOSPHERIC DEEP LAPSE RATES WILL SUPPORT SOME VERY WEAK
INSTABILITY...BUT THE LACK OF ANY APPRECIABLE MOISTURE WILL KEEP
MOST OF THE AREA FREE OF PRECIP.  SLIGHTLY HIGHER DEWPOINTS AND
MARGINALLY BETTER MOISTURE OVER THE NORTHERN COASTAL PLAIN SHOULD
LEAD TO A MORE PRONOUNCED CUMULUS FIELD...WHERE AN ISOLATED SHOWER
OR FEW SPRINKLES MAY BE POSSIBLE. HOWEVER...TO PROSPECTS ARE TOO LOW
TO INCLUDE IN THE FORECAST FOR WEDNESDAY. HIGHS WILL BE NOTICEABLY
COOLER WITH THICKNESSES DROPPING TO NEAR 1330M WEDNESDAY
MORNING...WHICH SHOULD YIELD LOW TO MID 60S.  SIMILAR THICKNESS
VALUES THURSDAY MORNING SUGGEST LOWS WILL BE MOSTLY IN THE UPPER 30S
TO MID 40S.

THE LOW WILL THEN SLOWLY MEANDER NORTHEAST ALONG THE MID-ATLANTIC
COAST THROUGH THE END OF THE WEEK...AS HIGH PRESSURE SETTLES AND
LINGERS OVER THE OHIO/TENN VALLEYS.  BETWEEN THESE FEATURES...DRY
WEATHER IS EXPECTED THROUGH THE PERIOD WITH NORTHWEST FLOW REMAINING
IN PLACE.  THE GFS AND ECMWF HAVE BEEN INDICATING A SHORTWAVE WILL
MOVE FROM THE NORTHERN PLAINS TOWARD THE SOUTHEAST US BY THE
WEEKEND...THOUGH THERE HAS BEEN A LOT OF DISAGREEMENT REGARDING THE
AMPLITUDE OF THE WAVE AND ITS FINAL DESTINATION.  THE 00Z/20TH
ECMWF...WHICH HAD BEEN SHOWING THE WAVE CUTTING OFF OVER THE DEEP
SOUTH...NOW SHOWS A MORE PROGRESSIVE WAVE THAT SWINGS ALL THE WAY
THROUGH THE REGION AND OFFSHORE BY SUNDAY...A SOLUTION THAT IS MORE
LIKE PREVIOUS GFS RUNS.  THE SENSIBLE IMPACTS OF THIS WAVE APPEAR TO
BE MINIMAL AS THE AIRMASS OVER NC WILL BE QUITE DRY AND
STABLE...WITH JUST A SLOW TREND IN TEMPS BACK TOWARD NORMAL THROUGH
THE WEEKEND.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
AS OF 655 AM MONDAY...

CIRRUS AND CALM THIS MORNING WILL YIELD TO A DEVELOPING SSW SURFACE
WIND THAT WILL BECOME OCCASIONALLY GUSTY INTO THE MID-UPPER TEENS
KTS MAINLY AT KINT/KGSO DURING THE MIDDAY-EARLY AFTERNOON HOURS...AS
HIGH PRESSURE DRIFTS OFF THE NC COAST. THE RETURN FLOW WILL ALSO
RESULT IN THE ONSHORE DEVELOPMENT/ADVECTION OF AN AREA OF
STRATOCUMULUS...THE WESTERN EDGE OF WHICH WILL PRODUCE SCATTERED TO
BROKEN CLOUD BASES AROUND 3500-4500 FT AT KFAY AND KRWI THIS
AFTERNOON AND EVENING. A FEW HOUR PERIOD OF MID LEVEL CEILINGS ABOVE
10 THOUSAND FEET AND VIRGA WILL OCCUR WITH THE WEST TO EAST PASSAGE
OF A MID LEVEL TROUGH TONIGHT.

OUTLOOK: THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC
STATES...AND ASSOCIATED PASSAGE OF A SURFACE COLD FRONT LATE TUE...
WILL RESULT IN A CHANCE OF SHOWERS TUE AFTERNOON THROUGH WED...
MAINLY FROM KRDU AND KRWI NORTHEAST TOWARD THE CHESAPEAKE BAY.

&&

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

&&

$$

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


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