Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270539 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 138 AM EDT TUE AUG 26 2014 .SYNOPSIS...
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HIGH PRESSURE WILL EXTEND SOUTHWARD INTO THE REGION TODAY. A BACK DOOR COLD FRONT WILL SETTLE SOUTH INTO CENTRAL NC THU AND THU NIGHT.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 955 PM TUESDAY... VERY FEW CHANGES TO THE FORECAST TONIGHT. DEEP LAYER RIDGING CONTINUES WEST OF THE MOUNTAINS WITH A DRY AIR RIDGE AT THE SURFACE ALONG THE EASTERN SEABOARD. A FEW THIN HIGH CLOUDS SPILLING OVER THE RIDGE WILL CONTINUE TO DRIFT OVERHEAD...BUT SHOULD HAVE LITTLE IMPACT ON TEMPS. DEWPOINTS ARE COMPARABLE TO LAST EVENING...AND WITH LIGHT WINDS OR CALM CONDITIONS...LOWS SHOULD END UP SIMILAR AS WELL. HURRICANE CRISTOBAL WELL OFF THE SOUTHEAST COAST WILL BEGIN TO MAKE ITS PASS BETWEEN NC AND BERMUDA...WHICH WILL INCREASE THE PRESSURE GRADIENT A LITTLE ALONG THE COAST AND KEEP NORTHEASTERLY WINDS STIRRED OVER THE COASTAL PLAIN. ISOLATED POCKETS OF FOG ARE POSSIBLE AS WELL. LOWS IN THE UPPER 50S TO LOWER 60S. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 240 PM TUESDAY... WEDNESDAY AND WEDNESDAY NIGHT: CENTRAL NC WILL BE SANDWICHED BETWEEN AN UPPER LEVEL RIDGE TO THE WEST AND HURRICANE CRISTOBAL WELL TO THE EAST. EXPECT HIGH PRESSURE TO REMAIN AT THE SURFACE...ALTHOUGH THE GRADIENT...AND THUS THE WINDS...WILL BE WEAKER THAN TODAY. THE STRONGEST WINDS/WIND GUSTS ARE EXPECTED TO BE ALONG AND OFF THE CAROLINA COAST. THE CONTINUED DRY AIR AT THE MID LEVELS AND NNE FLOW AT THE SURFACE SHOULD RESULT IN MOSTLY SUNNY/CLEAR SKIES FOR THE DAY/NIGHT. WITH THE LACK OF CLOUDS AND AN APPROX 15 METER INCREASE IN LOW LEVEL THICKNESSES FROM TUESDAY TO WEDNESDAY...EXPECT HIGH TEMPERATURES TO BE APPROX 5 DEGREES OR SO HIGHER THAN TODAY...UPPER 80S TO AROUND 90 DEGREES. WINDS WILL GENERALLY DECREASE AND BACK AROUND TO MORE WESTERLY OVERNIGHT AS CRISTOBAL MOVES NORTHEAST AWAY FROM NC. EXPECT LOWS MAINLY IN THE MID 60S. -KC FOR THU/THU NIGHT: STILL APPEARS LIKELY THAT THE BACKDOOR SURFACE FRONT WILL PUSH INTO FAR NE NC THU AFTERNOON... THEN CONTINUE DROPPING SLOWLY TO THE SSW... TO BE SITUATED FROM NW NC TO THE SRN OUTER BANKS BY LATE THU NIGHT. PRECISELY HOW FAR SSW THE FRONT GETS WILL DEPEND ON THE DENSITY OF THE PARENT HIGH NOSING DOWN FROM NY/PA. LOW LEVEL MASS CONVERGENCE ALONG THIS FRONT IS LIKELY TO BE THE PRIMARY FORCING MECHANISM... GIVEN THAT ANY DPVA WITHIN THE FAIRLY WEAK NW FLOW ALOFT WILL BE MINOR. THE GFS SHOWS A THIN STRIP OF MUCAPE UNDER 750 J/KG ACROSS THE FAR NORTHERN CWA LATE THU/THU NIGHT... ALTHOUGH THE NAM IS MORE UNSTABLE (1000-1500 J/KG) WITH A BIT MORE PROGRESSIVE (MORE TO THE SW) FRONT ACROSS CENTRAL NC. THE GFS HAS BETTER RUN-TO-RUN CONTINUITY ALONG WITH SUPPORT FROM THE ECMWF... AND ITS LOWER CAPE MAKES SENSE GIVEN THAT ITS DEW POINTS ARE 5-8 DEGREES COOLER AND MORE REASONABLE. DEEP LAYER SHEAR WILL REMAIN WEAK... WITH HIGHEST VALUES NEAR 25 KTS ONLY OVER THE NE CWA. WILL HOLD CLOSE TO EXISTING FORECAST CONVECTION CHANCES... WITH EXPECTATIONS OF AFTERNOON STORMS FORMING OVER THE NRN MOUNTAINS DRIFTING TO THE ESE ACROSS THE NRN CWA DURING THE LATE AFTERNOON AND EVENING BEFORE DIMINISHING GRADUALLY AND EXITING OVERNIGHT. COULD SEE SMALL LINGERING CAPE OVERNIGHT AS SURFACE DEW POINTS RECOVER. GIVEN THE LACK OF LOW LEVEL MOISTURE TRANSPORT AND SLOWLY RISING HEIGHTS ALOFT... HOLDING CONVECTIVE COVERAGE AS ISOLATED STILL LOOKS GOOD. MODELS KEEP TRENDING WARMER... GIVING THICKNESSES 10-15 M ABOVE NORMAL AND WARMING STATISTICAL GUIDANCE WITH EACH RUN... SUPPORTING ABOVE-NORMAL HIGHS OF 89-93 AND LOWS 67-70. -GIH && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 150 PM TUESDAY... FOR FRI/FRI NIGHT: THE WEAK SURFACE FRONT SHOULD BE STALLED ACROSS NC FROM NW TO THE CENTRAL COAST EARLY FRI... THEN START TO DISSOLVE WITH LOW LEVEL FLOW BECOMING SOUTHEASTERLY AS THE PROGRESSIVE PARENT HIGH TO THE NNE SHIFTS SWIFTLY OFF THE NORTHEAST COAST. WEAK LOW LEVEL CONFLUENT FLOW AND IMPROVED MOISTURE POOLING ALONG THE DYING FRONT MAY FUEL ANOTHER ROUND OF ISOLATED STORMS ACROSS THE NRN CWA... ALTHOUGH HEIGHTS WILL BE RISING ALOFT WITH THE DEPARTURE OF THE MID LEVEL TROUGH OFF THE CANADIAN MARITIMES... ALLOWING RIDGING TO BUILD OVER THE SOUTHEAST STATES... AND THIS WARMING AND STABILIZATION ALOFT SHOULD LIMIT COVERAGE. LITTLE CHANGE IN AIR MASS WITH THICKNESSES INCHING UPWARD... AND HIGHS SHOULD AGAIN BE WITHIN A FEW DEGREES OF 90 WITH LOWS IN THE UPPER 60S/AROUND 70. FOR SAT-TUE: THE DRY WEATHER EARLY IN THIS PERIOD WILL GRADUALLY GIVE WAY TO INCREASED STORM CHANCES HEADING INTO EARLY NEXT WEEK. THE MID LEVEL LOW NOW OVER NV WILL CONTINUE HEADING EASTWARD THEN NORTHEAST... DAMPENING AS IT GETS DRAWN UP BY PROGRESSIVE LONGWAVE TROUGHING OVER SRN CANADA. STRONG RIDGING WILL PERSIST ALONG THE SOUTHEAST COAST SAT... AND WITH THE SE/S LOW LEVEL FLOW REMAINING LIGHT... MOISTURE FLUX WILL BE SUBDUED. THE GFS DEPICTS MUCAPE VALUES RISING TO 1000-1500 J/KG SAT... BUT THE SMALL DEEP LAYER SHEAR UNDER 20 KTS WILL LIMIT STORM ORGANIZATION/STRENGTH. AND THERE MAY NOT BE ANY DISCERNIBLE BOUNDARY LEFT OVER CENTRAL NC TO FOCUS CONVECTION. GFS/ECMWF ARE BOTH FAIRLY DRY... SO WILL KEEP POPS SAT UNDER CLIMATOLOGY AT LESS THAN 15%. THE DAMPENED WAVE MOVES THROUGH THE ST LAWRENCE VALLEY SUN/SUN NIGHT... AND WHILE THIS MAY HELP TAMP DOWN THE RIDGE A BIT... THE ENSUING SW FLOW ALOFT REMAINS VERY LIGHT. SURFACE LEE TROUGHING IS EXPECTED TO FORM OVER CENTRAL NC... AND WITH IMPROVED LOW LEVEL MOISTENING AND RISING MLCAPE PREDICTIONS TO 1500-2000 J/KG OVER MUCH OF CENTRAL NC... WE SHOULD SEE A SMALL UPTICK IN CONVECTION CHANCES SUN/SUN NIGHT. OPERATIONAL MODEL DETAILS DIVERGE AFTER THIS TIME BUT IT APPEARS THAT HEIGHTS WILL BE ON THE SLOW RISE AGAIN MON/TUE... ALBEIT WITH A WEAK SHEAR AXIS POSSIBLY LAYING BACK THROUGH THE WRN PIEDMONT. THIS IS LIKELY TO LEAD TO A TREND BACK TOWARD CLIMATOLOGICALLY NORMAL POPS... SCATTERED MAINLY DURING THE AFTERNOON/EVENING... AND WILL RETAIN CHANCE POPS MON EXTENDING THROUGH TUE. THICKNESSES ARE PROJECTED TO HOLD ABOVE NORMAL BY AROUND 10 M... SO WILL STAY WITH HIGHS IN THE UPPER 80S TO AROUND 90 WITH LOWS IN THE UPPER 60S TO AROUND 70. -GIH && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 135 AM WEDNESDAY... 24 HOUR TAF PERIOD: CANADIAN HIGH PRESSURE OVERHEAD...BETWEEN A COLD FRONT APPROACHING FROM THE MIDWEST AND HURRICANE CRISTOBAL OFFSHORE...WILL RESULT IN MAINLY VFR CONDITIONS THROUGH THE TAF PERIOD. WINDS HAVE GENERALLY WENT CALM AT MOST SITES ACROSS CENTRAL NC THIS MORNING. WHILE WIDESPREAD FOG IS NOT EXPECTED... THINK WE WILL SEE AT LEAST SOME PATCHY SUB-VFR VISBYS THIS MORNING ACROSS THE EASTERN HALF OF THE AREA. CONFIDENCE IS INCREASING THAT KRWI MAY HAVE SOME MVFR VISBYS IN THE PRE-DAWN HOURS OF THIS MORNING. THUS... HAVE INCLUDED A TEMPO FOR KRWI FOR MVFR VISBYS IN THE 07-11Z TIME FRAME. IF SUB-VFR VISBYS DO INDEED DEVELOP AT KRWI... THEN WE COULD SEE THE FOG PRONE SITE VARY FROM MVFR TO IFR/LIFR UNTIL 11/12Z. CONFIDENCE AT KFAY AND KRDU IS STILL NOT HIGH ENOUGH TO INCLUDE ANY SUB-VFR PRE-DAWN VISBYS IN THEIR TAFS YET. AFTER SUNRISE THIS MORNING WE MAY AGAIN SEE A BRIEF PERIOD OF MVFR CIGS DEVELOP... THANKS TO THE CONTINUED MOIST NORTHEASTERLY LOW LEVEL FLOW... BEFORE LIFTING AND SCATTERING. ALTHOUGH... EXPECT IT TO BE VERY BRIEF AND LIMITED TO ONLY THE EASTERN SITES (KRDU/KFAY/KRWI)... AS LOW LEVEL FLOW WILL BE BACKING TO MORE OF A NORTHERLY DIRECTION AS HURRICANE CRISTOBAL LIFTS NORTHWARD AND PASS WELL OFFSHORE TODAY. OTHERWISE... A GENERALLY LIGHT NORTHERLY SFC WIND IS EXPECTED TODAY (5-10 KTS). HOWEVER... THERE WILL LIKELY BE A SHORT PERIOD OF SOMEWHAT STRONGER WINDS (8-12 KTS WITH GUSTS INTO THE MID-UPPER TEENS KTS... MAINLY AT KFAY/KRWI) AT EASTERN SITES MID-MORNING TO MIDDAY TODAY...WHERE THE MSLP PRESSURE GRADIENT WILL BE RESIDUALLY TIGHT EARLY IN THE DAY...BETWEEN THE OVERHEAD SFC HIGH AND THE OFFSHORE HURRICANE. OUTLOOK: THE ARRIVAL OF THE COLD FRONT APPROACHING FROM THE UPPER MIDWEST WILL RESULT IN A SMALL CHANCE OF AN AFTERNOON SHOWER OR STORM THU AND FRI...AS WELL AS A CHANCE OF MVFR CEILINGS IN BRIEF NE FLOW THU NIGHT FROM KRWI AND ESPECIALLY POINTS NORTHEASTWARD... INTO NE NC AND TIDEWATER VA. THE PROBABILITY OF PATCHY FOG WILL ALSO INCREASE BY THE WEEKEND...AS THE LOW LEVEL FLOW ASSUMES A MORE SOUTHERLY (MOIST) COMPONENT.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BSD/MWS NEAR TERM...KC/BLS SHORT TERM...KC/HARTFIELD LONG TERM...HARTFIELD AVIATION...BSD/MWS

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