Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011830 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 230 PM EDT MON SEP 1 2014 .SYNOPSIS...AN AREA OF HIGH PRESSURE WILL EXTEND OVER THE REGION THROUGH TUESDAY. A WEAK SURFACE FRONT WILL SETTLE SOUTHWARD ACROSS CENTRAL NC ON WEDNESDAY. HIGH PRESSURE WILL BUILD BACK OVER THE AREA FOR THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1020 AM MONDAY... ONLY SLIGHT ADJUSTMENT REQUIRED TO THE NEAR TERM FORECAST...BASED ON 12Z UPPER AIR ANALYSIS AND OBSERVED TEMPERATURE TREND. PATCHES OF EARLY MORNING FOG/LOW CLOUDS HAVE LIFT/DISSIPATED ACROSS MUCH OF THE REGION. 12Z UPPER AIR ANALYSIS DEPICTS AN AREA OF HIGH PRESSURE CENTERED OVER THE SC/GA COAST...STRETCHING NORTH INTO THE PIEDMONT/COASTAL PLAIN OF NC. THE PRESENCE OF THIS WEATHER FEATURE WILL LIKELY INHIBIT CONVECTIVE DEVELOPMENT ACROSS MUCH OF THE FORECAST AREA. LATEST WRF/MESO MODEL ANALYSIS SUGGEST THAT CONVECTIVE DEVELOPMENT LATE THIS AFTERNOON-EARLY EVENING SHOULD BE NO WORSE THAN ISOLATED. THUS HAVE TRIMMED THE SMALL CHANCE/SLIGHT CHANCE POP A BIT ACROSS SECTIONS OF THE PIEDMONT AND COASTAL PLAIN. 12Z AREA SOUNDINGS CONTINUE TO DEPICTS QUITE A BIT OF DRY AIR PRESENT IN THE LOW-MID LAYERS OF THE ATMOSPHERE. MIXING OF THIS DRIER AIR TO THE SURFACE SHOULD CAUSE SURFACE DEWPOINTS TO FALL INTO THE MID 60S ACROSS MOST OF THE PIEDMONT...WHILE DEWPOINTS IN THE UPPER 60S/AROUND 70 WILL BE COMMON IN THE SANDHILLS AND COASTAL PLAIN. THICKNESSES SUPPORT AFTERNOON TEMPS IN THE LOW-MID 90S SO LITTLE ADJUSTMENT REQUIRED IN THIS UPDATE. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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AS OF 230 PM MONDAY... (FROM 315 AM MONDAY) HOT AND HUMID CONDITIONS CONTINUE ON TUESDAY... WITH H85 TEMPS AGAIN AROUND 20C AND SOUTHERLY FLOW AROUND THE BERMUDA HIGH. A SHORTWAVE CROSSING THE GREAT LAKES WILL LEAD TO SOME VERY WEAK HEIGHT FALLS OVER VIRGINIA AND NC...WHICH SHOULD INCREASE CONVECTIVE COVERAGE AMIDST MLCAPE OF 1000-2000 J/KG AND PW OVER 1.75 INCHES. SHEAR IS FORECAST TO REMAIN RELATIVELY WEAK...HOWEVER...AND THE BETTER SEVERE THREAT SHOULD ACCORDINGLY REMAIN TO OUR NORTH. HIGHS IN THE MID 90S AND HEAT INDICES AROUND 100F IN THE EAST. THE WEAK HEIGHT FALLS ALOFT AND LINGERING OUTFLOW BOUNDARIES MAY HELP MAINTAIN SOME SHOWERS/STORMS INTO THE OVERNIGHT HOURS TUESDAY NIGHT...WITH MOST ACTIVITY DWINDLING AFTER MIDNIGHT. LOWS IN THE UPPER 60S AND LOWER 70S. -BLS FOR WED/WED NIGHT: THE WEAK SURFACE REFLECTION THAT REMAINS FROM THE COLD FRONT APPROACHING CENTRAL NC WILL BECOME EVEN MORE WASHED OUT AS IT SHIFTS INTO THE LEE TROUGH OVER CENTRAL NC. MODELS SHOW A VERY WEAK VORTICITY LOBE ASSOCIATED WITH THIS FRONT PUSHING ESE THROUGH NC EARLY WED... AND ITS APPROACH ALONG WITH LINGERING STRONG LOW LEVEL MOISTURE TRANSPORT OVER ERN NC SHOULD SUPPORT AN AREA OF ATYPICAL MORNING SHOWERS/STORMS OVER THE ERN AND ESPECIALLY SE CWA WED MORNING. THE DEPARTURE AND DAMPENING OF THE MEAN MID LEVEL TROUGH WELL TO OUR NE WILL RESULT IN MODEST RISING HEIGHTS (15-25 M) WITHIN THE FLAT (W-E ORIENTED) MID LEVEL RIDGE ACROSS NC THROUGH WED NIGHT. THE LATEST NAM RUN IS CONSISTENT WITH PREVIOUS RUNS IN BRINGING LOWER PW (UNDER 1.5") INTO MUCH OF THE CWA FROM THE NW WITH A BIT STRONGER 850-700 MB NW WIND AS COMPARED TO THE GFS... WHICH KEEPS PW VALUES UP TO 1.7-1.9". GIVEN THE FACT THAT THE MID LEVEL TROUGH WILL BE DAMPENING WITH LITTLE REASON TO SUPPORT A STRONG PUSH OF DRY AIR PAST THE MOUNTAINS... THE GFS`S MORE SUBDUED TROUGH INFLUENCE APPEARS MORE LIKELY... BASED ON THE PERSISTENCE OF THE STRONG RIDGE. MODERATE INSTABILITY IS EXPECTED OVER ALL BUT PERHAPS THE FAR NW... WITH THE GFS SHOWING MUCAPE PEAKING AT 1000-2500 J/KG. WILL STAY CLOSE TO THE GFS/ECMWF SOLUTION WITH SCATTERED AFTERNOON THROUGH EVENING STORMS... WITH BEST COVERAGE ACROSS THE SOUTHERN CWA AND ALONG/EAST OF THE PERSISTENT LEE TROUGH... AS WELL AS ALONG THE INLAND-TRACKING SEA BREEZE. WITH ABOVE-NORMAL PW AND WEAK MID LEVEL FLOW... SLOW-MOVERS AND HEAVY-RAINERS ARE POSSIBLE. WITH THICKNESSES A TAD LOWER THAN TUE BUT REMAINING 12-20 M ABOVE NORMAL... EXPECT WARM AND STICKY HIGHS OF 91-95... DESPITE A GOOD CHANCE OF DEBRIS CLOUD COVER THROUGH THE DAY. CONVECTION CHANCES SHOULD RECEDE WED NIGHT BUT THE GFS INDICATES PLENTY OF ELEVATED BUOYANCY POTENTIAL OVERNIGHT... INCLUDING MLCAPE OF 500-1000 J/KG RESULTING FROM VERY WARM 960-920 MB TEMPS. WILL HOLD ONTO CHANCE POPS MAINLY SOUTH HALF OVERNIGHT. MUGGY LOWS IN THE LOW-MID 70S. -GIH
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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AS OF 230 PM MONDAY... FOR THU/FRI: CONTINUED ABOVE-NORMAL WARMTH WITH ONLY MINOR CHANGES IN AIR MASS. AT THE SURFACE... THE WEAK LEE TROUGH HOLDS THROUGH CENTRAL NC... ALONG WITH A HUMID AND SOMEWHAT STAGNANT AIR MASS. A POSITIVELY TILTED TROUGH SHIFTS THROUGH THE PACIFIC NORTHWEST AND SW CANADA INTO THE DAKOTAS THU... RESULTING IN BUILDING HEIGHTS AND GRADUAL MID LEVEL WARMING OVER THE SOUTHEAST STATES. THIS POLAR STREAM TROUGH THEN SHIFTS INTO ERN CANADA... WHILE THE FLAT RIDGE HOLDS ACROSS NC. WITH PLENTY OF LOW LEVEL MOISTURE POOLING... ISOLATED TO SCATTERED STORMS FOCUSED ALONG A SEA BREEZE OR SOME OTHER SUBTLE BOUNDARY REMAIN A GOOD BET... DESPITE THE WARMING TEMPS ALOFT. WILL RETAIN AFTERNOON AND EVENING STORM CHANCES BOTH DAYS... WITH TEMPS HOLDING ABOUT A CATEGORY ABOVE NORMAL AS THICKNESSES STAY 10-15 M ABOVE NORMAL. FOR SAT THROUGH MON: A PATTERN TRANSITION IS LIKELY NEXT WEEKEND. THE INITIAL MID LEVEL TROUGH CONTINUES HEADING EASTWARD OVER ERN CANADA EARLY SAT... HOWEVER A SLUG OF STRONG VORTICITY EMANATING FROM A STRONG COLD VORTEX OVER THE BEAUFORT SEA WILL PUSH EASTWARD CLOSE ON ITS HEELS... TAKING A COLD FRONT TO NEW ENGLAND AND THE OH VALLEY BY EARLY SAT. THE RESULTING TROUGH OVER ERN NOAM SUNDAY SHOULD HELP PUSH THE FRONT SOUTHWARD INTO NC... AFTER WHICH TIME IT IS APT TO LAY WEST/EAST AND STALL OVER THE CAROLINAS FOR LATE SUN THROUGH MON. THE GFS HAS A STRONGER/FASTER TIME FRAME THAN THE ECMWF... WITH THE FORMER MODEL SOLUTION TAKING THICKNESSES MUCH COLDER... UP TO 25 M BELOW NORMAL AS OPPOSED TO THE ECMWF WHICH IS BARELY 5 M BELOW NORMAL. TOUGH TO RESOLVE SUCH DIFFERENCES BUT GIVEN THE STRENGTH OF THE SRN CONUS RIDGE... AND THE FAR-NORTH TRACK OF THE POLAR LOW... I REMAIN SKEPTICAL ABOUT A STRONG COLD FRONTAL PASSAGE THROUGH NC. WILL STAY ON THE CONSERVATIVE SIDE OF THE TEMP TREND... WITH HIGHS/LOWS INITIALLY AROUND 90/AROUND 70 SAT... SLIPPING TO LOW-MID 80S/UPPER 60S BY MON. PRECIP CHANCES AND PATTERNS ARE LIKELY TO CHANGE LITTLE THROUGH SUN... PERHAPS INCREASING IN COVERAGE AS THE FRONT APPROACHES WITH FALLING HEIGHTS ALOFT... STRENGTHENING (YET STILL SOMEWHAT WEAK) MID LEVEL FLOW... AND A PERSISTENT CONFLUENT INFLUX OF GULF AND ATLANTIC MOISTURE IN THE LOW LEVELS. WILL MAINTAIN SCATTERED SHOWERS AND STORMS FOCUSED ON -- BUT NOT RESTRICTED TO -- AFTERNOON AND EVENING HOURS. WILL KEEP A CLIMO CHANCE POP ON MON... WITH LOWER THAN USUAL CONFIDENCE AS CONVECTION WILL GREATLY DEPEND ON WHETHER THE FRONT HOLDS UP ACROSS NC OR SHIFTS TO OUR SOUTH. -GIH
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/... AS OF 120 PM MONDAY... VFR CONDITIONS WILL CONTINUE ACROSS MUCH OF CENTRAL NC THROUGH TUESDAY NIGHT. THE EXCEPTION WILL BE A GOOD PROBABILITY OF EARLY STRATUS AND FOG (AND ASSOCIATED IFR/LIFR CONDITIONS)OCCURRING NEAR KRWI...KFAY AND POTENTIALLY NEAR KRDU. THE FOG/STRATUS WILL BE MOST LIKELY BETWEEN 09Z-12Z. ANY CONVECTION THIS AFTERNOON WILL BE LIMITED TO THE SEABREEZE WHICH MAY TRIGGER AN ISOLATED THUNDERSTORM NEAR OR SOUTH OF KGSB AND KRWI AND TO THE EAST-SE OF KFAY. THE SAME STORY WILL HOLD FOR TUESDAY AFTERNOON THOUGH AN ISOLATED THUNDERSTORM MAY OCCUR IN VICINITY OF KINT AND KGSO LATE IN THE DAY INTO THE EVENING HOURS. THE WEATHER PATTERN MAY BECOME A LITTLE MORE UNSETTLED WEDNESDAY AS A WEAK SURFACE BOUNDARY WILL DRIFT INTO CENTRAL NC. THIS FEATURE WILL SERVE AS A FOCUS FOR THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS...MAINLY IN THE AFTERNOON-EVENING HOURS. THIS BOUNDARY IS PROJECTED TO WEAKEN THURSDAY WHILE HIGH PRESSURE WILL BUILD BACK INTO THE REGION FRIDAY AND SATURDAY. OTHERWISE...THE OCCURRENCE OF EARLY MORNING FOG/STRATUS WILL CONTINUE THROUGH THE PERIOD. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...BLS/HARTFIELD LONG TERM...HARTFIELD AVIATION...WSS

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