000 FXUS62 KRAH 081134 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 735 AM EDT MON SEP 8 2008 .SYNOPSIS...A WEAK SURFACE BOUNDARY SITTING OVER NORTH CAROLINA WILL PUSH TO THE NORTHWEST TODAY... ALLOWING WEAK HIGH PRESSURE TO BRIEFLY BUILD OVER THE AREA THROUGH TUESDAY. A COLD FRONT WILL APPROACHES THE AREA FROM THE NORTH TUESDAY NIGHT. A COOLER AIR MASS AND CLOUDY CONDITIONS ARE EXPECTED BEHIND THIS FRONT FOR WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 310 AM MONDAY... CONDITIONS APPEAR FAVORABLE FOR SOME PATCHY DENSE FOG THIS MORNING...AS SEVERAL SITES ACROSS THE SOUTHEAST ARE ALREADY REPORTING VISIBILITY RESTRICTIONS BELOW 2 STATUE MILES. WILL CONTINUE TO MONITOR THIS TREND AND ISSUE DENSE FOG ADVISORY OR SPECIAL WEATHER STATEMENT AS NEEDED. OTHERWISE...TODAY WILL BE NEARLY A CARBON COPY FROM SUNDAY AS BL THERMAL STRUCTURE IS NEARLY IDENTICAL TODAY TO SUNDAY...AS CENTRAL NC REMAINS UNDER A WEAK AND VARIABLE SURFACE PATTERN. THUS EXPECT HIGHS TODAY IN THE UPPER 80S TO LOWER 90S. CONVECTIVE COVERAGE WILL BE ISOLATED AGAIN TODAY. AND WHILE IT WILL BE HARD TO RULE OUT A LONE CUMULONIMBI ANYWHERE ACROSS THE FORECAST AREA...SOUTHERN AND EASTERN AREAS WILL BE THE FAVORED LOCATION...WHERE DEEPEST MOISTURE AND HIGHER INSTABILITY WILL EXIST. THE SYNOPTIC PATTERN ALSO FAVORS CONVECTIVE DEVELOPMENT ALONG THE HIGHER TERRAIN...WITH WEAK UPSLOPE FLOW...MAKING THE EXTREME WESTERN CWA A SECONDARY FAVORED AREA FOR ISOLATED STORMS WELL INTO THE LATE EVENING HOURS. FORECAST SOUNDINGS INDICATE THE POTENTIAL FOR SOME STRATUS/FOG DURING THE PREDAWN HOURS TUESDAY. LOWS IN THE UPPER 60S TO LOWER 70S. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... AS OF 310 AM MONDAY... TUESDAY...STRONG DAYTIME HEATING FEATURING AFTERNOON TEMPERATURES IN THE MID TO UPPER 80S...FUEL STEEP LOW-LEVEL LAPSE RATES WITH MLCAPE VALUES OF 1500 TO 2200 JOULES TUESDAY AFTERNOON WITH THE APPROACH OF COLD FRONT FROM THE NW. WEAK MID-LEVEL SHEAR AXIS AND SOUTHERN FRINGES OF 65KT UPPER JET MOVING ACROSS THE AREA...RESULT IN RATHER IMPRESSIVE UNIDIRECTIONAL DEEP LAYER SHEAR OF 30 TO 35 KTS BY 18Z TUESDAY. COULD MOST DEFINITELY SEE A FEW STORMS REACH SEVERE LIMITS...WITH MAIN THREAT BEING FROM DAMAGING STRAIGHT LINE WINDS FROM PRECIP DOWNLOADING. KEPT POPS IN THE HIGH CHANCE RANGE. TUESDAY NIGHT THROUGH THURSDAY...RAISED POPS TO LOW LIKELY ACROSS THE NORTH TUESDAY NIGHT/WEDNESDAY MORNING...THEN SHIFTING THE LIKELY POPS ACROSS THE SOUTH DURING THE DAY ON WEDNESDAY AS MODELS INDICATE PWATS BETWEEN 1.8 TO 1.9"...RATHER STRONG BAROCLINIC BOUNDARY PASSAGE AND UPPER DIVERGENCE IN ENTRANCE REGION OF EXITING JET. BOTH THE GFS AND NAM INDICATE THE FRONT IS SOUTH OF THE AREA BY 18Z. HOWEVER MODELS INDICATE ANA-FRONTAL PRECIP WELL INTO EVENING AND OVERNIGHT HOURS AS...AS BROAD REGION OF LOW-LEVEL SELY ONSHORE FLOW OVERTAKES THE SOUTHEAST AS IKE ENTERS THE GULF. TRANSITION CONVECTIVE PRECIP TO STRATIFORM PRECIP FROM NORTH TO SOUTH THROUGH THE DAY...WITH DRIZZLE BECOMING LIKELY WEDNESDAY NIGHT AS 500MB HEIGHTS RISE OVER THE AREA. UPPER CONFLUENCE OVER THE NORTHEAST LOOKS TO ANCHOR 1027 TO 1029 MB SURFACE HIGH ON THURSDAY...RESULTING IN A LATE SUMMER WEAK/HYBRID DAMMING EVENT ON THURSDAY...AS WEAK SELY ONSHORE FLOW RIDES ATOP THE WEDGE DOME. THE GFS TRIES TO BRING THE COASTAL TROUGH INLAND THURSDAY AFTERNOON...BRINGING THE THREAT OF THUNDER IN THE COASTAL PLAIN. HAVE KEPT POPS IN THE SMALL CHANCE CATEGORY...WITH HIGHEST POPS IN THE SOUTHEAST. MADE VERY LITTLE CHANGES TO BELOW NORMAL TEMPERATURES WEDNESDAY AND THURSDAY...WITH THURSDAY BEING THE MOST CHALLENGING THROUGH THE PERIOD. CURRENT FORECAST ALREADY HAS HIGH TEMPERATURES A CATEGORY BELOW GUIDANCE FOR THURSDAY...WITH HIGHS IN THE MID TO UPPER 70S. HOWEVER DEPENDING ON QPF AMOUNTS...TEMPERATURES COULD STRUGGLE TO REACH THE 70S ACROSS THE PIEDMONT. && .LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 330 AM MONDAY... THE LATEST MODEL GUIDANCE AGREES THAT THE COLD AIR DAMMING PARENT HIGH PRESSURE WILL SHIFT OFF THE NOVA SCOTIA COAST BY FRIDAY MORNING. GIVEN THE LACK OF AN ANCHORING MECHANISM FOR THE HIGH... THIS MOVEMENT MAKES SENSE... HOWEVER IT MAY NOT NECESSARILY TRANSLATE INTO A QUICK DISSOLUTION OF THE WEDGE AIR MASS OVER NC. TRYING TO TIME THE BREAKUP OF THE WEDGE REGIME IS ONE OF THE MORE DIFFICULT FORECAST PROBLEMS IN THIS REGION... ESPECIALLY SEVERAL DAYS OUT. NEVERTHELESS... DESPITE THE INITIAL STABLE NATURE OF THE DAMMING HIGH (WHICH CURRENTLY CONTAINS DEW POINTS IN THE UPPER 30S-LOWER 40S)... CONSIDERING THE PARENT HIGH`S CORE IS MOVING OUT QUICKLY... THUS ENDING LARGE SCALE SUPPORT FOR THE DAMMING... AND WITH THE SEPTEMBER SUNSHINE IS STILL STRONG ENOUGH TO INDUCE PLENTY OF VERTICAL MIXING... WE SHOULD SEE THE WEDGE BREAK FRIDAY AFTERNOON. LOW LEVEL MOISTURE SHOULD REMAIN ABUNDANT THOUGH... LEADING TO DESTABILIZATION... SO WILL HOLD ONTO A CHANCE OF THUNDERSTORMS FRIDAY AFTERNOON/EVENING. COVERAGE WILL DEPEND A GREAT DEAL ON THE STRENGTH OF THE MID LEVEL ATLANTIC RIDGE NOSING INTO NC FROM THE EAST. THE ECMWF HAS A STRONGER RIDGE AND HENCE LESS COVERAGE AS COMPARED TO THE WEAKER RIDGE ON THE GFS. WILL KEEP POPS 30-40% FOR NOW. TEMPERATURES SHOULD BE NEAR NORMAL IN THE NW PIEDMONT... THE LAST TO BREAK OUT OF THE MORE STABLE AIR... AND ABOVE NORMAL ELSEWHERE. IKE IS STILL EXPECTED TO MAKE LANDFALL OVER THE WESTERN GULF COAST EARLY IN THE WEEKEND... AND THE 18Z/07 GFS AND THE 00Z/08 ECMWF AGREE WITH THIS SCENARIO... TAKING IKE ON A MORE NORTHWARD JOURNEY THROUGH THE LOWER MISS VALLEY WHILE KEEPING MORE MID LEVEL RIDGING OVER NC. HOWEVER THE 00Z/80 GFS IS NOW SHOWING IKE SITTING LONGER OFF THE LA COAST BEFORE LANDFALLING OVER THE WRN FL PANHANDLE SUNDAY NIGHT... AND WITH ITS FASTER NORTHERN STREAM LONGWAVE TROUGH TO OUR NW... IT BRINGS MUCH MORE MOISTURE INTO NC AHEAD OF A COLD FRONT. WILL NOT MAKE ANY MAJOR CHANGES AT THIS TIME... KEEPING LOW CHANCE POPS OVER THE WEEKEND... BUT WE WILL NEED TO WATCH CLOSELY WHAT HAPPENS TO IKE AFTER LANDFALL... IF IT GETS THERE. LOW LEVEL THICKNESSES REMAIN VERY WARM SO WILL HOLD ONTO TEMPERATURES AT LEAST A CATEGORY OR TWO ABOVE NORMAL BOTH DAYS. -GIH && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 155 AM MONDAY... A WEAK SURFACE BOUNDARY WILL PERSIST OVER CENTRAL NC THROUGH THIS MORNING BEFORE PUSHING NORTHWESTWARD THIS AFTERNOON. THIS BOUNDARY IS CURRENTLY SEPARATING THE SLIGHTLY LOWER HUMIDITY IN NW NC... WHERE SURFACE DEW POINTS ARE IN THE MID-UPPER 60S AND FOG IS MINIMAL... FROM THE MORE HUMID AIR OVER THE SOUTHEAST HALF OF NC... WHERE DEW POINTS ARE IN THE 70-75 DEGREE RANGE AND WHERE AREAS OF LIFR FOG DEVELOPED. RWI AND FAY WILL CONTINUE TO SEE A THREAT OF LIFR FOG AND RESULTANT STRATUS UNTIL IT LIFTS MID MORNING. THE REMAINDER OF TODAY WILL BE LARGELY VFR. AS THIS WEAK BOUNDARY HEADS TOWARD THE MOUNTAINS... A LIGHT WIND FROM THE SE WILL PREVAIL. ISOLATED STORMS ARE POSSIBLE... AND WHILE IT IS DIFFICULT TO TELL WHERE CONVECTION WILL INITIATE... THE INLAND-MOVING SEA BREEZE ALONG WITH THE HIGHER TERRAIN TO OUR NW MAY BE THE FIRST PLACES TO SEE A STORM. HAVE INCLUDED A CB MENTION IN INT/GSO... ALTHOUGH ANY MOUNTAIN CONVECTION IS LIKELY TO MOVE VERY SLOWLY TO THE NE AND MAY NOT GET CLOSE TO THESE TAF SITES. HAVE ALSO INCLUDED A CB AT FAY WHERE INSTABILITY IS LIKELY TO BE HIGHEST AND WHERE THE SEA BREEZE MAY END UP. AFTER MIDNIGHT... FOG IS LIKELY TO REDEVELOP WITH EVEN GREATER BOUNDARY LAYER MOISTURE. LIFR VSBYS ARE LIKELY AT RWI/FAY... AND IFR FOG IS PROBABLE AT RDU. NO WORSE THAN MVFR FOG IS EXPECTED AT INT/GSO... ALTHOUGH AVIATION INTERESTS SHOULD CERTAINLY KEEP UP WITH THE LATEST VSBY FORECASTS INTO TONIGHT. LOOKING BEYOND TONIGHT... MUCH OF THIS WEEK WILL SEE ADVERSE AVIATION CONDITIONS. MORE IFR/LIFR CIGS/VSBYS ARE LIKELY TO DEVELOP TONIGHT... PARTICULARLY AT RWI/FAY WHERE THE LOW LEVEL MOISTURE WILL BE HIGHEST/DEEPEST LEADING TO WIDESPREAD LOW CLOUDS AND DENSE FOG. NUMEROUS SHOWERS AND STORMS ARE EXPECTED LATE TUESDAY THROUGH TUESDAY NIGHT WITH COLD FRONT PASSAGE... AND THESE MAY PRODUCE MVFR CIGS/VSBYS. CIGS ARE LIKELY TO BECOME IFR BY WEDNESDAY MORNING WITH MOISTURE OVERRUNNING THE FRONT WITH RAIN FALLING INTO A COOL SURFACE HIGH NOSING DOWN FROM THE NORTH. THESE LOW CLOUDS MAY NOT IMPROVE MARKEDLY BEFORE FRIDAY. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...CBL SHORT TERM...CBL LONG TERM...HARTFIELD AVIATION...HARTFIELD
NWS RAH Office Area Forecast Discussion