Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 181824 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 224 PM EDT THU SEP 18 2014 .SYNOPSIS...HIGH PRESSURE CENTERED NORTHEAST OF THE GREAT LAKES WILL EXTEND DOWN THROUGH VIRGINIA AND THE CAROLINAS THROUGH THE WEEKEND... AS IT SLIDES EAST. A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATE SUNDAY... THEN MOVE SOUTHEAST THROUGH THE REGION MONDAY. && .NEAR TERM /THROUGH FRIDAY NIGHT/... AS OF 220 PM THURSDAY... THROUGH TONIGHT: QUIET AND DRY NIGHT FOR MOST. SURFACE MAP SHOWS A WEAK MSLP PATTERN OVER NC WITH A WEAK INVERTED TROUGH OVER THE WRN PIEDMONT... HELPING TO FOCUS MOISTURE IN THE LOWEST 5-6 THOUSAND FT IN THIS AREA AND FOSTERING DEVELOPMENT OF VERY ISOLATED SHALLOW SHOWERS. THESE SHOULD PERSIST INTO THE EVENING HOURS... GIVEN THIS WEAK LOW LEVEL MASS CONVERGENCE IN CONJUNCTION WITH WEAK TERRAIN UPGLIDE... BUT WITH A CAPPING INVERSION EVIDENT AT 775-750 MB AND WARM/DRY/STABLE AIR ABOVE... EXPECT DEVELOPMENT TO BE STUNTED BOTH VERTICALLY AND IN COVERAGE... AS PW REMAINS BELOW NORMAL. THE LATEST SEVERAL HRRR RUNS SUPPORT THIS AS WELL. WILL KEEP AN ISOLATED SHOWER CHANCE IN THE WRN AND EXTREME SW CWA THROUGH THE EVENING. OTHERWISE... FORECAST SOUNDINGS SHOW THE LOW LEVEL MOISTURE GRADUALLY DISPERSING WITH TIME... STILL GREATER OVER THE WRN CWA THAN IN THE EAST... SO EXPECT MOSTLY CLEAR SKIES EAST AND PARTLY CLOUDY WEST. SLOWLY LOWERING SURFACE DEWPOINTS SHOULD LOWER THE RISK OF FOG... EXCEPT PERHAP IN THE WRN CWA NEAR THE SURFACE TROUGH. BASED ON LAST NIGHT`S LOWS AND STATISTICAL GUIDANCE... EXPECT LOWS OF 58-63. FOR FRI/FRI NIGHT: RAIN CHANCES WILL REMAIN LOW. THE MID LEVEL TROUGH AXIS IS EXPECTED TO BE SHIFTING TO OUR SE WITH RISING HEIGHTS ALOFT. LOW LEVEL MOISTURE TRANSPORT PERSISTS BUT IS CONFINED TO THE FAR SRN AND SE CWA... WHERE PW VALUES WILL HOVER NEAR 1.4-1.5". THE ONSHORE-DIRECTED LOW LEVEL STEERING FLOW COULD DRAW SHALLOW SEA BREEZE SHOWERS INLAND OVER THE FAR SE CWA. ISOLATED UPSLOPE- SUPPORTED SHOWERS REMAIN POSSIBLE IN THE FAR WRN CWA AS WELL. IN GENERAL HOWEVER... THE TRADITIONAL MODELS REMAIN TOO WET... SHOWING PRECIP COVERING THE MAJORITY OF THE CWA... WHICH APPEARS UNLIKELY GIVEN THE LACK OF FORCING AND INSTABILITY WITH LIMITED MOISTURE. WILL KEEP ISOLATED POPS ALONG THE WRN/SRN AND SE EDGES OF THE CWA FRI AFTERNOON INTO THE EVENING. THICKNESSES ARE EXPECTED TO DIP SLIGHTLY... INDICATING HIGHS OF 76-81. LOWS 56-61 WITH PARTLY CLOUDY SKIES WEST AND MOSTLY CLEAR EAST. -GIH && .SHORT TERM /SATURDAY THROUGH SUNDAY/...
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AS OF 224 PM THURSDAY... SATURDAY AND SATURDAY NIGHT: HEIGHTS ALOFT WILL CONTINUE TO RISE OVER THE CAROLINAS ON SATURDAY...AS AN EXTENSION OF THE MID LEVEL RIDGE CENTERED OVER THE CENTRAL US RIDGE NOSES NORTHEASTWARD INTO THE AREA...SANDWICHED BETWEEN THE AMPLIFYING NORTHERN STREAM DIVING SEWD OUT OF SOUTHERN CANADA AND THE REMNANT LOW ALONG THE SOUTHEAST COAST. AT THE SURFACE...DRY AIR SURFACE RIDGE AXIS WILL WEDGE SOUTHWESTWARD DOWN THE MID ATLANTIC STATES AND THROUGH THE CAROLINAS AND GEORGIA. RESULTANT LOW PWATS AND A STABLE AIR COLUMN WILL SECURE DRY CONDITIONS. HIGHS IN THE UPPER 70S TO LOWER 80S. LOWS SATURDAY NIGHT UPPER 50S TO LOWER 60S. SUNDAY: AMPLIFYING/DIGGING NORTHERN STREAM TROUGH AND ASSOCIATED POLAR WESTERLIES WILL PICK UP THE LINGERING AREA OF LOW PRESSURE NEAR THE SOUTHEAST COAST AND KICK IT EAST-NORTHEASTWARD...LIFTING UP THE NC COAST AND THEN OUT INTO THE ATLANTIC ON SUNDAY. LITTLE TO NO SENSIBLE WEATHER IMPACTS ARE EXPECTED FROM THIS FEATURE...BUT A PRE- FRONTAL TROUGH IS EXPECTED TO DEVELOP IN THE LEE OF THE MOUNTAINS SUNDAY AFTERNOON...OWING TO THE APPROACH OF THE NORTHERN STREAM TROUGH. WOULD NOT BE SURPRISED TO SEE AN ISOLATED SHOWER DEVELOP INVOF OF THIS TROUGH...BUT WILL KEEP FORECAST DRY. SUNDAY LOOKS TO BE THE WARMEST DAY IN THE NEXT FORESEEABLE FUTURE WITH LOW-LEVEL THICKNESSES PROJECTED TO CLIMB 20 METERS ABOVE NORMAL...HIGHS IN THE LOWER TO MID 80S.
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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AS OF 224 PM THURSDAY... SUNDAY NIGHT THROUGH MONDAY: 40 TO 60 METER HEIGHT FALLS TRAVERSING THE REGION IN ADVANCE OF THE AMPLIFYING NORTHER STREAM TROUGH ADVANCING EASTWARD INTO THE EASTERN US WILL DRIVE A SURFACE COLD FRONT INTO THE AREA LATE SUNDAY NIGHT/EARLY MONDAY MORNING . WRT THE COLD FRONTAL PASSAGE ON MONDAY...THE GFS HAS TRENDED TOWARDS THE FASTER SOLUTION OF THE EC...WHICH HAS THE FRONT SOUTH AND EAST OF THE AREA BY 18Z MONDAY. GIVEN THE FASTER TIMING...SUFFICIENT INSTABILITY WILL BE LACKING AND GIVEN LIMITED MOISTURE AVAILABILITY...CONVECTIVE/RAIN CHANCES REMAIN UNIMPRESSIVE. WILL LEAVE IN SLIGHT CHANCE POPS...BUT FROPA COULD END BEING A NON- MEASURABLE/SPRINKLE EVENT FOR MUCH OF THE CWA. FASTER FROPA WILL RESULT IN SLIGHTLY COOLER TEMPERATURES MONDAY AFTERNOON. HIGHS IN THE UPPER 70S NW TO LOWER 80S SE. TUESDAY THROUGH THURSDAY: LIKE CLOCKWORK...A STRONG +1030MB CANADIAN SURFACE HIGH... ANCHORED UNDERNEATH THE UPPER CONFLUENCE ZONE IN THE WAKE OF THE EXITING UPPER TROUGH/CLOSED LOW OVER SOUTHERN NEW ENGLAND...WILL PROVIDE THE FIRST DAYS OF FALL(AUTUMNAL EQUINOX BEGINS MONDAY SEPT 22 AT 10:29 PM EDT)WITH BONA FIDE FALL CONDITIONS. DRY WITH TEMPERATURES 5-8 DEGREES BELOW NORMAL. HIGHS 70 TO 75. LOWS IN THE LOWER TO MID 50S...WITH SOME UPPER 40S POSSIBLE WEDNESDAY NIGHT ACROSS THE NORTHERN PIEDMONT.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 145 PM THURSDAY... VFR CONDITIONS ARE LIKELY TO HOLD THROUGH THE TAF FORECAST PERIOD. EARLIER MVFR CIGS AT INT/GSO HAVE MIXED OUT TO SCATTERED... ALTHOUGH THESE MAY STILL GO BROKEN BRIEFLY PRIOR TO 20Z. OTHERWISE... ANY CLOUDS THROUGH TONIGHT AND FRI MORNING SHOULD BE BASED ABOVE 3 000 FT AGL... MORE LIKELY TO BE BROKEN AT INT/GSO WITH LESS COVERAGE AT RDU/RWI/FAY. LIGHT AND VARIABLE WINDS MAINLY FROM THE NE WILL CONTINUE TONIGHT AT SPEEDS MAINLY UNDER 6 KTS... THEN SHOULD INCREASE TO 7-10 KTS FROM THE ENE AFTER 14Z FRI. LOOKING BEYOND 18Z FRI... VFR CONDITIONS SHOULD DOMINATE THROUGH AT LEAST SUNDAY... ALTHOUGH MVFR FOG IS POSSIBLE EARLY SAT MORNING AS THE LIGHT ONSHORE LOW LEVEL FLOW PERSISTS. A PERIOD OF MVFR CIGS IS POSSIBLE LATE SUN INTO SUN NIGHT AHEAD OF A COLD FRONT. VFR CONDITIONS SHOULD THEN RETURN FOR MON/TUE WITH HIGH PRESSURE BUILDING IN FROM THE NW. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...CBL LONG TERM...CBL AVIATION...HARTFIELD

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