Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171852 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 253 PM EDT WED SEP 17 2014 .SYNOPSIS...HIGH PRESSURE WILL CONTINUE TO BUILD IN FROM THE NORTH TONIGHT... AND REMAIN OVER THE AREA THROUGH SATURDAY. A COLD FRONT WILL APPROACH FROM THE NORTHWEST SUNDAY... THEN MOVE SOUTHEAST THROUGH THE REGION MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 245 PM WEDNESDAY... THROUGH TONIGHT: A FEW SHOWERS/STORMS ARE POSSIBLE MAINLY IN THE COASTAL PLAIN THIS EVENING... BUT OTHERWISE EXPECT QUIET WEATHER TONIGHT WITH PARTLY TO MOSTLY CLOUDY SKIES. THE SURFACE FRONT REMAINS WELL TO OUR SOUTH THIS AFTERNOON... WITH SOMEWHAT WEAK HIGH PRESSURE BUILDING IN FROM THE NORTH. THE RESULTING LOW LEVEL EASTERLY FLOW OFF THE ATLANTIC CONTINUES TO DRAW SUFFICIENT MOISTURE INTO CENTRAL NC FOR BROKEN CLOUD COVER... ESPECIALLY OVER THE HIGHER TERRAIN WHERE FORCED UPGLIDE IS LEADING TO MORE DENSE CLOUD DEVELOPMENT. CINH AND LOW CAPE VALUES DOMINATE THE FAR NRN AND WRN CWA ACCORDING TO MESOANALYSES... ALTHOUGH IN EASTERN SECTIONS FROM RALEIGH TO THE EAST AND SOUTHEAST...MLCAPE HAS RISEN ABOVE 500 J/KG... AND EFFECTIVE SHEAR HERE A WEAK MID LEVEL WAVE NOW TRAVERSING THE REGION MAY PROVIDE A SLIGHT BIT OF DEEPER FORCING FOR ASCENT TO AUGMENT THE INSTABILITY... ALTHOUGH DYNAMICS ARE GENERALLY QUITE WEAK. OTHERWISE... THE COLUMN IS DRIER IN THE WRN CWA WITH BELOW-NORMAL PW... AND CONVECTION FOR THE REMAINDER OF TODAY INTO TONIGHT APPEARS UNLIKELY HERE. MODELS WITH BOTH EXPLICIT AND PARAMETERIZED CONVECTION HAVE GENERALLY OVERDONE PRECIP OVER THE AREA SO FAR TODAY... AND EVEN THESE ARE TRENDING DRIER OVERNIGHT. WILL HOLD INTO LOW CHANCE POPS FROM THE TRIANGLE EAST INTO EARLY EVENING... TRENDING DOWN BY LATE EVENING/OVERNIGHT. HAVE RETAINED A MENTION OF PATCHY DRIZZLE OVERNIGHT... AS WE KEEP A PREDOMINANTLY EASTERLY MOIST LOW LEVEL FLOW... HOWEVER THE MODELS` DEPICTION OF MOIST ISENTROPIC UPGLIDE IS WEAK AT BEST TONIGHT... SO EXPECT MINIMAL IMPACT. WE SHOULD CONTINUE TO SEE BROKEN CLOUDS OVERNIGHT HOWEVER... ESPECIALLY IN THE WRN PIEDMONT AND SOUTHWEST... WHERE WE SHOULD HAVE ADDITIONAL MID/HIGH CLOUDS AS A RESULT OF THE REMNANT MCV -- NOW OVER SRN MO/NRN AR -- EXPECTED TO SKIRT BY JUST TO OUR SOUTHWEST LATE TONIGHT. LOWS 58-63. -GIH && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 340 AM WEDNESDAY... THURSDAY...MINOR S/W PROJECTED TO PASS ACROSS THE FORECAST AREA IN THE MORNING. WEAK SUBSIDENCE IN ITS WAKE IN THE AFTERNOON AND ADVECTION OF DRIER AIR WILL BEGIN EROSION OF RESIDUAL CAD AIR MASS IN THE PIEDMONT. HOWEVER...MODELS TYPICALLY ARE TOO AGGRESSIVE WITH THIS TRANSITION. FAVOR A SLOWER IMPROVEMENT TREND THAN ADVERTISED BY THE MODELS. THIS LEADS TO MAX TEMPS ON THE COOL SIDE OF GUIDANCE. IF EROSION IS EVEN SLOWER THAN EXPECTED...MAX TEMPS MAY BE AS MUCH A 3- 4 DEGREES TOO WARM IN THE PIEDMONT. CONVECTION THURSDAY AFTERNOON APPEARS LIMITED TO THE FAR EAST-SE SECTIONS. JUST WEAK INSTABILITY AND SHEAR PROJECTED SO EXPECT MAINLY ISOLATED SHOWERS IN THE COASTAL PLAIN/SANDHILLS. MAX TEMPS MID-UPPER 70S NORTH TO AROUND 80 SOUTH. THURSDAY NIGHT...EXPECT GRADUAL IMPROVEMENT IN SKY CONDITIONS. THIS MAY LEAD TO SOME PATCHY FOG BUT INTRUSION OF DRIER AIR NEAR THE SURFACE MAY LIMIT/INHIBIT FOG FORMATION. BEST CHANCE FOR FOG WILL LIKELY BE THE SE HALF. MIN TEMPS IN THE UPPER 50S NW TO THE LOWER 60S SE. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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AS OF 300 PM WEDNESDAY... FRIDAY THROUGH SATURDAY: EASTERN US TROUGH WILL PULL EAST AND OUT TO SEA OUT ON FRIDAY... BUT NOT WITHOUT LEAVING BEHIND A REMNANT MID- LEVEL CIRCULATION TO MEANDER OFF THE SE COAST THROUGH EARLY SUNDAY. AT THE SURFACE...PROGRESSIVE CANADIAN HIGH OVER NEW ENGLAND WILL QUICKLY MOVE EAST OUT INTO THE NORTHERN ATLANTIC...BECOMING ELONGATED AS IT SHIFTS FARTHER OFFSHORE. IN THE WAKE OF THE EXITING TROUGH...HEIGHTS INCREASE OVER THE AREA...WHICH SHOULD KEEP THE MID- LEVEL CIRCULATION OFF THE SE COAST AT BAY AND SECURE DRY CONDITIONS ACROSS CENTRAL NC. AS FAR AS TEMPERATURES...PROGRESSIVE NATURE OF THE PARENT HIGH AND ORIENTATION OF THE ASSOCIATED RIDGE AXIS IS EXPECTED TO YIELD A LONG FETCH OF EAST-NORTHEASTERLY LOW-LEVEL MARITIME FLOW INTO THE AREA AND KEEP THE BRUNT OF THE COOLER AND DRIER AIR TO OUR NORTH...WHILE SUPPORTING PERIODIC PARTLY TO BROKEN CLOUDINESS IN THE WAY OF MORNING STRATUS AND A DIURNALLY ENHANCED CU FIELD. HIGHS IN THE MID 70S NORTH TO AROUND 80 SOUTH. LOWS FRIDAY NIGHT IN THE MID 50S NORTH TO NEAR 60 SOUTH. LOWS SATURDAY NIGHT A GOOD CATEGORY WARMER...IN THE UPPER 50S TO LOWER 60S. SUNDAY THROUGH MONDAY: 40 TO 60 METER HEIGHT FALLS TRAVERSING THE REGION IN ADVANCE OF THE AMPLIFYING UPPER LEVEL TROUGH SWINGING EASTWARD ACROSS THE EASTERN US WILL DRIVE A SURFACE COLD FRONT THROUGH THE AREA MONDAY AFTERNOON. IN ADVANCE OF THE UPPER TROUGH...AFOREMENTIONED MID-LEVEL CIRCULATION/LOW OFF THE SOUTHEAST COAST WILL FINALLY GET KICKED EAST-NORTHEASTWARD...LIFTING UP THE NC COAST AND THEN OUT INTO THE ATLANTIC ON SUNDAY. THE LATEST 12Z/17 GFS IS STRONGER WITH THIS FEATURE AND SUGGEST IT COULD POTENTIALLY ENHANCE THE ONSHORE MARITIME FLOW...POSSIBLY RESULTING IN SLIGHTLY CLOUDIER/COOLER CONDITIONS...MAINLY ACROSS EASTERN PORTIONS OF THE FORECAST AREA ON SUNDAY. OTHERWISE...WITH LOW-LEVEL THICKNESSES PROJECTED TO CLIMB 20 METERS ABOVE NORMAL...HIGHS IN THE LOWER TO MID 80S. THERE ARE SOME MINOR MODEL TIMING DIFFERENCES WITH FROPA ON MONDAY...WITH THE EC A GOOD 12 HOURS FASTER TO PUSH THE FRONT THROUGH THE AREA. GIVEN LIMITED/SHALLOW MOISTURE AVAILABILITY...CONVECTION ALONG THE FRONT WILL NEED TO UTILIZE FAVORABLE DIURNAL TIMING/INSTABILITY TO SUPPORT SLIGHT/SMALL CHANCE POPS MONDAY AFTERNOON/EARLY EVENING. TUESDAY AND WEDNESDAY: BELOW NORMAL TEMPERATURES ARE EXPECTED UNDERNEATH THE EASTERN US TROUGH AND SUPPORTED IN THE LOW-LEVELS BY NORTHERLY FLOW VIA BUILDING STRONG ~1030MB SURFACE HIGH. HIGHS 70 TO 75. LOWS IN THE 50S.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 150 PM WEDNESDAY... CURRENT PREDOMINATING MVFR CONDITIONS ARE EXPECTED TO SLOWLY RISE TO LOW-END VFR PRIOR TO 22Z. THESE VFR CONDITIONS SHOULD HOLD UNTIL THE 04Z-07Z TIME FRAME... WHEN IFR CIGS MAY DEVELOP ACROSS THE AREA... LASTING UNTIL AROUND 12Z-13Z THU MORNING. A COLD FRONT HAS SETTLED SOUTH OF NC... WITH COOL HIGH PRESSURE BUILDING IN FROM THE NORTH. A MOIST EASTERLY FLOW OF AIR IN THE LOW LEVELS OFF THE ATLANTIC IS GENERATING THE CURRENT CLOUD COVER OVER CENTRAL NC. THIS FLOW WILL PERSIST THROUGH TONIGHT... WITH REDEVELOPMENT OF LOW CLOUDS LATE TONIGHT AS THE LOWER LEVELS STABILIZE. ANY LOW CLOUDS TONIGHT SHOULD MIX OUT AND LIFT TO VFR BETWEEN 13Z AND 15Z THU. THERE IS A RISK OF STORMS NEAR RWI/FAY THIS AFTERNOON UNTIL AROUND 22Z OR 23Z... BUT OTHERWISE MOSTLY DRY WEATHER IS EXPECTED. HOWEVER... PATCHY MVFR VSBY IN DRIZZLE IS POSSIBLE TONIGHT BETWEEN 07Z AND 12Z. LOOKING BEYOND 18Z THU... VFR CONDITIONS SHOULD DOMINATE THU AFTERNOON AND EVENING. IFR CIGS AND MVFR/IFR VSBYS ARE POSSIBLE THU NIGHT FROM 06Z UNTIL 13Z FRI MORNING... AND AGAIN BETWEEN 08Z AND 12Z SAT MORNING... AS THE LIGHT ONSHORE LOW LEVEL FLOW PERSISTS. OTHERWISE... VFR CONDITIONS ARE EXPECTED AT CENTRAL NC TERMINAL FORECAST SITES... AS A RIDGE OF HIGH PRESSURE EXTENDS THROUGH THE AREA. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...WSS LONG TERM...CBL AVIATION...HARTFIELD

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