Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171849 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 245 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 TUESDAY/... AS OF 340 AM WEDNESDAY... A PORTION OF THE LONGWAVE TROUGH INITIALLY ALONG THE EAST COAST WILL BE LEFT BEHIND...OFFSHORE THE SE US COAST THIS WEEKEND...BUT THE OTHERWISE DEAMPLIFYING/LIFTING TROUGH WILL YIELD TO RISING HEIGHTS ALOFT OVER THE CAROLINAS...AS A FLAT MID LEVEL RIDGE RIDGE NOSES EASTWARD FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY. THE RE- ESTABLISHMENT AND AMPLIFICATION OF A WESTERN NOAM RIDGE WILL THEN RESULT IN DOWNSTREAM TROUGH AMPLIFICATION FROM SOUTH-CENTRAL CANADA TO THE EAST-CENTRAL US DAYS 5-7. BENEATH THE RISING HEIGHTS ALOFT...A CANADIAN-SOURCE SFC HIGH (AROUND 1030 MB) WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES AND RIDGE SOUTH/SOUTHWESTWARD THROUGH THE EASTERN STATES THROUGH THE FIRST HALF OF THE WEEKEND...BEFORE YIELDING - AMIDST FALLING HEIGHTS DOWNSTREAM OF THE AFOREMENTIONED REDEVELOPING TROUGH ALOFT HEADED FOR THE EAST-CENTRAL US - TO APPALACHIAN-LEE SFC TROUGH DEVELOPMENT SUN...AND A PASSING COLD FRONT MON-MON NIGHT. THOUGH THE CANADIAN RIDGING WILL RESULT IN A RELATIVELY PROLONGED PERIOD OF EAST TO NORTHEAST LOW LEVEL FLOW THROUGH EARLY THIS WEEKEND...THE LATEST GUIDANCE SUGGESTS THE BRUNT OF THE ASSOCIATED COOLER AND DRIER AIR WILL HOLD OVER THE NORTHERN MIDDLE ATLANTIC AND NORTHEAST STATES. IN ADDITION...THE ORIENTATION OF THE LOW LEVEL RIDGE AXIS SHOULD ALSO DIRECT MARITIME MOISTURE/CLOUDS AROUND THE RIDGE...TO THE SOUTH OF CENTRAL NC. AS SUCH...SKIES ARE APT TO BE PARTLY TO MOSTLY SUNNY OVER CENTRAL NC...WITH TEMPERATURES ABOUT A CATEGORY WARMER THAN EARLIER ANTICIPATED...IN THE MIDDLE 70S TO AROUND 80 DEGREES FRI-SAT. WARMER YET AHEAD OF THE APPROACHING FRONT SUN-MON - LIKELY LOWER TO PERHAPS MIDDLE 80S...WITH JUST A SLIGHT CHANCE OF SHOWERS ATTENDING THE FRONT LATE MON...GIVEN A LIMITED GULF MOISTURE FEED. COOLER TUE...AND THOUGH THERE REMAINS SOME POTENTIAL FOR LINGERING LIGHT RAIN (ESPECIALLY EAST) PER THE 12Z EC...THE 00Z EC HAS TRENDED TOWARD THE MORE CONSISTENT AND FAVORED EC ENSEMBLE MEAN WITH A "CLEANER" FRONTAL PASSAGE AND DRIER SOLUTION FOR TUE. && .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...MWS AVIATION...HARTFIELD

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