Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260027 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 827 PM EDT FRI JUL 25 2014 .SYNOPSIS...A STALLED FRONT WILL REMAIN NEAR OR JUST SOUTH OF THE SOUTH CAROLINA BORDER THROUGH TONIGHT. A CLIMATOLOGICALLY MOIST AND UNSTABLE AIRMASS WILL PREVAIL OVER THE WEEKEND. AN UNSEASONABLY DEEP UPPER LEVEL TROUGH AND ATTENDANT COLD FRONT WILL APPROACH FROM THE NORTHWEST SUNDAY NIGHT...THEN CROSS THE REGION ON MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 PM FRIDAY... OUTFLOW ASSOC/W CONVECTION THAT DEVELOPED ALONG THE COLD FRONT TRACKING SOUTHWARD THROUGH VA/NC YESTERDAY EVENING SERVED TO 1) STRENGTHEN THE FRONTAL ZONE AND 2) ACCELERATE THE FRONT SOUTHWARD. AS A RESULT OF THE AFOREMENTIONED ACCELERATION...THE FRONT WAS LOCATED WELL SOUTH OF CENTRAL NC THIS MORNING...EXTENDING ROUGHLY WEST-EAST FROM ATLANTA-COLUMBIA-MYRTLE BEACH AT 14Z. WV IMAGERY AND RAOB DATA INDICATED A DRY/SUBSIDENT AIRMASS OVER CENTRAL NC THIS MORNING...IN THE WAKE OF PRONOUNCED SHORTWAVE ENERGY LOCATED OFFSHORE THE MID-ATLANTIC COAST AT 14Z. ALTHOUGH SFC DEWPOINTS HAVE FALLEN INTO THE MID/UPPER 60S IN MOST AREAS AND LOW-LEVEL MOISTURE HAS CERTAINLY DECREASED IN COMPARISON TO YESTERDAY...SUFFICIENT LOW- LEVEL MOISTURE STILL EXISTS FOR MARGINAL DIURNAL DESTABILIZATION WITH MLCAPE PROGGED IN THE 250-1000 J/KG RANGE...LOWEST NEAR THE VA BORDER AND HIGHEST NEAR THE SC BORDER. SHALLOW LOW-LEVEL CONVERGENCE ALONG THE STALLED FRONT SHOULD REMAIN SOUTH OF CENTRAL NC TODAY... AND WOULD BE MORE LIKELY TO SERVE AS A FOCUS FOR CONVECTIVE DEVELOPMENT OVER CENTRAL/UPSTATE SC WHERE GREATER DESTABILIZATION IS EXPECTED. CYCLONIC FLOW ALOFT WILL PERSIST OVER THE REGION TODAY... AND SUBSIDENCE IN THE WAKE OF EXITING SHORTWAVE ENERGY SHOULD EFFECTIVELY SUPPRESS DEVELOPMENT THROUGH THE AFTERNOON. ADDITIONAL SHORTWAVE ENERGY (UPSTREAM IN IL/IN AT 14Z) WILL TRACK INTO THE SOUTHERN MID-ATLANTIC LATE TONIGHT...HOWEVER...DPVA ASSOC/W THIS FEATURE WILL OCCUR WELL INTO THE NOCTURNAL COOLING CYCLE...WITH LITTLE OR NO INSTABILITY AND NO CHANCE FOR CONVECTION. LOWS IN THE MID/UPPER 60S TONIGHT. -VINCENT && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... AS OF 300 PM FRIDAY... SAT/SAT NIGHT: THE MEAN TROUGH AXIS OVER THE EASTERN US WILL SHIFT OFFSHORE ON SAT...WITH CYCLONIC FLOW ALOFT SHIFTING INTO THE ATLANTIC AND AN INCREASINGLY NW FLOW ALOFT OVER THE CAROLINAS. WITH STRONG INSOLATION AND LINGERING LOW-LEVEL MOISTURE...DIURNAL DESTABILIZATION WILL BE BETTER THAN TODAY WITH MLCAPE VALUES PROGGED AT 500-1500 J/KG. SUBSIDENCE ON THE WESTERN PERIPHERY OF THE OFFSHORE TROUGH SHOULD SUPPRESS CONVECTIVE DEVELOPMENT FOR MOST (IF NOT ALL) OF THE DAY SAT...WITH FORCING OTHERWISE CONFINED TO VERY SHALLOW CONVERGENCE ASSOC/W A PIEDMONT SFC TROUGH. UNLESS POTENT SHORTWAVE ENERGY PROGRESSES INTO THE REGION IN NW FLOW ALOFT DURING THE EVENING HOURS (DOES NOT APPEAR LIKELY AT THIS TIME)...ANTICIPATE LITTLE CHANCE FOR TOWERING CU TO SURVIVE WITHIN AN OTHERWISE DRY/ HOSTILE AIRMASS. HIGHS IN THE LOWER 90S...LOWS IN THE LOWER TO MID 70S. -VINCENT SUN/SUN NIGHT: A SHORTWAVE TROUGH MOVING OUT OF CANADA AND ACROSS THE GREAT LAKES SUNDAY WILL BEGIN THE AMPLIFICATION OF THE LONGWAVE PATTERN FOR NEXT WEEK. EXPECT CONVECTION CONVECTION TO BE ONGOING OVER THE CENTRAL APPALACHIANS EARLY SUNDAY....WHICH SHOULD CONTINUE EAST INTO VA AND MAY BLEED SOUTH ALONG OUTFLOW INTO THE NORTHERN PORTIONS OF THE CWA. THE 12Z GFS BACKED OFF SIGNIFICANTLY ON THE COVERAGE OF CONVECTION OVER VA...SO CHANCE POPS ACROSS THE NORTHERN PIEDMONT AND COASTAL PLAIN ARE STILL A LITTLE UNCERTAIN. THE BIGGER STORY ON SUNDAY WILL BE THE HEAT AND HUMIDITY...AS DEEP MIXING AND 850MB TEMPS IN EXCESS OF 21C WILL LEAD TO HIGHS IN THE MID AND UPPER 90S. THE GFS EVEN SUGGESTS 100 IN A FEW SPOTS. MIXING WILL DROP DEWPOINTS A BIT...ESPECIALLY WEST OF THE PIEDMONT TROUGH...BUT TO THE EAST DEWPOINTS ARE FORECAST TO REMAIN IN THE UPPER 60S TO AROUND 70. THE RESULTING HEAT INDEX VALUES ARE IN THE 100-105 RANGE FOR A FEW HOURS AND MAY NECESSITATE A HEAT ADVISORY. A SOUTHWEST WIND WILL CONTINUE OVERNIGHT SUNDAY NIGHT AND LOWS WILL BE MUGGY IN THE MID TO EVEN UPPER 70S. MON/MON NIGHT: A STRONG COLD FRONT APPROACHING FROM THE NORTHWEST WILL CROSS THE CWA ON MONDAY AS ADDITIONAL SHORTWAVE ENERGY DIVES THROUGH THE BACKSIDE OF THE UPPER TROUGH. UNSEASONABLY STRONG 40- 60M HEIGHT FALLS OVERSPREADING WHAT IS EXPECTED TO BE A MOIST AND MODERATELY UNSTABLE AIRMASS WILL AID IN THE DEVELOPMENT OF STORMS ALONG AND AHEAD OF THE FRONT. BASED ON 40-50KT OF 0-6KM BULK SHEAR ASSOCIATED WITH THE DEEP PUSH OF THE STRONG WESTERLIES AND LONG...THERE IS GOOD CONFIDENCE THAT SUPERCELLS WITH A LARGE HAIL AND DAMAGING WIND THREAT WILL BE POSSIBLE. THE BIGGEST QUESTION WILL BE EXACTLY WHERE THE LEE TROUGH SETS UP AND HOW MUCH DEWPOINTS MIX OUT AS WEST-SOUTHWESTERLY LOW-LEVEL FLOW STRENGTHENS. EAST OF THE TROUGH...MOST LIKELY FROM US HWY 1 EAST...MODERATE INSTABILITY IS EXPECTED WITH FAIRLY STEEP MID-LEVEL LAPSE RATES OF -6C/KM TO MAYBE EVEN -7C/KM. FORECAST SOUNDINGS ALSO SHOW RATHER DRY MID- LEVEL AIR...THOUGH THE FORCING AND INSTABILITY SHOULD BE ABLE TO OVERCOME THIS...AND THE DRY AIR WILL LIKELY ENHANCE DAMAGING WIND THREAT. AT THE MOMENT...CONFIDENCE IS STRONG THAT SEVERE WEATHER WILL BE POSSIBLE...BUT THE UNCERTAINTY LIES HOW FAR EAST STORMS WILL DEVELOP AND THE OVERALL COVERAGE. HIGHS MONDAY WILL BE IN THE LOW TO MID 90S. -BLS && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 PM FRIDAY... IN THE WAKE OF THE THE FRONT ON MONDAY MEDIUM RANGE ENSEMBLES AND DETERMINISTIC MODELS SHOW AN UNSEASONABLY DEEP UPPER TROUGH DEVELOPING OVER THE EASTERN US BY MID WEEK WITH AN UPPER LOW CENTERED JUST SOUTH OF THE HUDSON BAY. MOST OF THE WEEK APPEARS TO BE STABLE WITH HIGH PRESSURE SETTLING ACROSS THE MID-ATLANTIC STATES AND DEWPOINTS IN THE UPPER 50S AND LOWER 60S. LOW-LEVEL THICKNESSES ARE PROGGED TO DIP BELOW 1390M...WHICH SUGGESTS HIGHS IN THE LOW/MID 90S AND LOWS IN THE LOW/MID 60S... POSSIBLY TOUCHING THE UPPER 50S IN THE COOLEST SPOTS. MORE UNCERTAINTY ARISES LATER IN THE WEEK WITH MODELS SHOWING SOME DEGREE OF FLOW SEPARATION WHERE AN UPPER LOW CUTS OFF AND DRIFTS SOUTH. WHETHER OR NOT THIS OCCURS REMAINS TO BE SEEN...SO AT THIS POINT WILL JUST HAVE A SLIGHT CHANCE POP BY FRIDAY AS MOISTURE STARTS TO INCREASE BACK ACROSS THE AREA. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... AS OF 815 PM FRIDAY... 24-HR TAF PERIOD: VFR CONDITIONS ARE GENERALLY EXPECTED FOR THE REMAINDER OF THE EVENING WITH ONLY A VERY LOW PROBABILITY OF SOME MVFR CIGS AT KFAY THROUGH 02Z. LOW LEVEL FLOW TONIGHT IS EXPECTED TO BECOME MORE SOUTHWESTERLY... HELPING TO FAVOR LESS IN THE WAY OF WIDESPREAD SUB-VFR CONDITIONS AREAWIDE. STILL GIVEN THE AMOUNT OF LOW LEVEL MOISTURE FROM RECENT RAINFALL AND EASTERLY TO SOUTHERLY FLOW TODAY... THINK WE CLOUD SEE A LEAST SOME PATCHY IFR-MVFR CIGS AND VISBYS ACROSS THE AREA. GUIDANCES CONTINUES TO HINT AT THE BEST CHANCE FOR PREVAILING SUB-VFR CONDITIONS IN THE PRE-DAWN HOURS ACROSS THE WESTERN PIEDMONT (KGSO/KINT). THUS... CONFIDENCE IS HIGHEST AT KGSO AND KINT FOR IFR CONDITIONS IN THE 08-14Z TIME FRAME... WITH PERHAPS SOME LINGERING MVFR STRATOCUMULUS INTO THE LATE MORNING. EXPECT VFR CONDITIONS WILL RETURN BY EARLY AFTERNOON AT THE LATEST AREAWIDE... WITH ONLY A SMALL CHANCE OF AFTERNOON/EVENING SHOWERS AND STORMS. LOOKING AHEAD: A COLD FRONT WILL APPROACH FROM THE NW SUNDAY/EARLY NEXT WORK WEEK... BRINGING THE POTENTIAL FOR SHOWERS/STORMS AND SUB- VFR CONDITIONS LATE SUNDAY (IN THE NORTHWEST) INTO MONDAY... PARTICULARLY MONDAY (ESPECIALLY EAST). VFR CONDITIONS ARE EXPECTED TO RETURN BEHIND THE FRONT ON TUESDAY AND CONTINUE THROUGH AT LEAST MID WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...VINCENT/BLS LONG TERM...BLS AVIATION...BSD

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