Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 131448 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1045 AM EDT SAT SEP 13 2014 .SYNOPSIS...A FRONTAL ZONE MEANDERING OVER THE REGION WILL BRING UNSETTLED WEATHER TO CENTRAL NC THROUGH EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1045 AM SATURDAY... ...FLASH FLOOD WATCH IN EFFECT ACROSS THE SOUTHERN PIEDMONT... SANDHILLS... AND SE COASTAL PLAIN AS HEAVY RAIN REMAINS A CONCERN THROUGH EARLY SUNDAY... A FEW AREAS OF LIGHT RAIN CONTINUE...MAINLY AROUND THE TRIANGLE AREA...BUT ARE DRYING UP QUICKLY. A WARM FRONT IS WORKING ITS WAY NORTH THROUGH THE AREA AHEAD OF A COLD FRONT MOVING THROUGH THE MOUNTAINS IN RESPONSE TO A SHORTWAVE EXITING THE GREAT LAKES REGION. THESE FRONTS SHOULD ESSENTIALLY MERGE OVER THE PIEDMONT THIS AFTERNOON AND SERVE AS THE FOCUS FOR CONVECTION THIS AFTERNOON BEFORE PUSHING BACK SOUTH THROUGH THE AREA TONIGHT. LOW STRATUS STILL COVERS THE ENTIRE CWA AS OF 14Z AND HAS YET TO SHOW ANY STRONG SIGNS OF LIFTING DESPITE A SOUTHERLY COMPONENT TO THE SURFACE WIND. THE STRATUS IS STICK BASED ON THE KGSO RAOB AND RAP FORECAST SOUNDINGS SUGGEST THE STRATUS WILL LINGER INTO THE EARLY AFTERNOON...WHICH WILL HAMPER DESTABILIZATION FOR A WHILE. ONCE BREAKS IN THE CLOUDS DO DEVELOP...POTENTIAL HEATING AND DEWPOINTS IN THE LOW 70S WILL SUPPORT 1000 TO MAYBE 1500 J/KG MLCAPE DESPITE WEAK LAPSE RATES ALOFT. BLENDED TPW SHOWS PW STILL OVER 2 INCHES ACROSS THE SOUTHERN CWA AND THE SWEET SPOT FOR INSTABILITY AND MOISTURE LOOKS TO FAVOR AREAS SOUTH OF A LINE FROM ROUGHLY ROCKINGHAM TO WILSON. THE MOST RECENT CAMS ALSO REFLECT THIS FOCUS ON THE SOUTHEASTERN TIER OF COUNTIES. NOT MAKING MANY ADJUSTMENTS TO THE THE FORECAST OTHER THAN TO REDUCE POPS IN THE NEXT FEW HOURS AWAITING BETTER INSTABILITY. THE FLASH FLOOD WATCH WILL CONTINUE AS IS. SHOULD SEE TEMPS EVENTUALLY MAKE IT INTO THE MID 70S NORTH TO MID 80S SOUTH IF CLOUDS EARLY ENOUGH THIS AFTERNOON. -BLS THE FRONT AND ASSOCIATED PRECIP ARE EXPECTED TO SHIFT SOUTH OF THE AREA TONIGHT AS STRONGER HIGHER PRESSURE RIDGES INTO SOUTH INTO THE REGION. THERE COULD SOME BRIEF BREAKS IN THE CLOUDS BEHIND THE FRONT...BUT THE COOL...MOIST NORTHEASTERLY FLOW BEHIND THE FRONT WILL ULTIMATELY LEAD TO SOME COLD AIR DAMMING SETTING UP ACROSS THE REGION...WITH LOW CLOUDS/FOG/DRIZZLE POSSIBLE SATURDAY NIGHT. OVERNIGHT LOWS SHOULD RANGE FROM THE LOWER 60S ACROSS THE NORTHWEST TO THE UPPER 60S FURTHER SOUTHEAST. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... AS OF 300 AM SATURDAY... MODELS HAVE TRENDED DRIER FOR SUNDAY AS THE FRONT AND THE MORE SIGNIFICANT PRECIP GETS SHUNTED TO OUR SOUTH. THEREFORE...WILL LOWER POPS...BUT NOT COMFORTABLE REMOVING THEM ALL TOGETHER YET. HOWEVER...HIGH PRESSURE RIDGING DOWN INTO THE REGION WILL RESULT IN A COLD AIR DAMMING SET UP ACROSS THE REGION. THEREFORE CONSIDERABLE CLOUDINESS WILL PERSIST ACROSS THE REGION...WITH MAYBE EVEN SOME DRIZZLE/LIGHT RAIN (HENCE NOT WANTING TO GO WITH A DRY FORECAST). SO REGARDLESS OF PRECIP CHANCES...TEMPS SHOULD REMAIN WELL BELOW NORMAL FOR AT LEAST ANOTHER DAY...WITH HIGHS GENERALLY RANGING FROM THE UPPER 60S ACROSS THE NORTHWEST TO THE MID 70S FURTHER SOUTH AND EAST. OVERNIGHT LOWS SHOULD FALL INTO THE LOWER 60S WITH SOME UPPER 50S IN THE USUAL COLDER LOCATIONS. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 305 AM SATURDAY... MONDAY AND MONDAY NIGHT...BOTH THE NAM AND THE GFS FORECAST DRYING IN THE MEAN WITH THE GFS FORECASTING SHORT-TERM 850MB THETA-E TROUGHING DURING THE MORNING. AS A MID-LEVEL SHORTWAVE APPROACHES LATE IN THE DAY AND IN THE EVENING...THETA-E VALUES START TO INCREASE AGAIN...SHIFTING GRADUALLY EAST ACROSS CENTRAL NORTH CAROLINA IN THE HIGHER VALUES OVERNIGHT. THE HIGHEST PRECIPITABLE WATER VALUES ARE FORECAST OVER SOUTHERN PARTS OF CENTRAL NORTH CAROLINA MONDAY NIGHT...CLOSER TO WHERE WEAK SURFACE WAVES SHOULD BE MOVING ALONG THE PRIMARY SURFACE FRONT LOCATED JUST TO THE SOUTH OF CENTRAL NORTH CAROLINA. FOR THE DAY MONDAY...BUFR SOUNDINGS ARE LARGELY STABLE TO DEEP CONVECTION EXCEPT LATE IN THE DAY WHEN INSTABILITY IS FORECAST TO INCREASE TO AROUND 500J/KG...LESS IN MOST AREAS NORTH OF U.S. 64. AFTER WHAT IS EXPECTED TO BE A DRY MORNING WILL NOTE A CHANCE OF SHOWERS AND THUNDERSTORMS SOUTH OF U.S. 64 MONDAY AFTERNOON WITH A SLIGHT CHANCE NORTH OF THERE. MONDAY NIGHT...IN THE BETTER MOISTURE AND CLOSER TO THE SURFACE FRONT WILL SHOW LIKELY CHANCES FOR SHOWERS IN THE SANDHILLS AND SOUTHERN COASTAL PLAIN WITH SOLID CHANCES ELSEWHERE. LAPSE RATES STEEPEN A LITTLE OVERNIGHT AS BUFR SOUNDINGS SHOW MODEST COOLING ALOFT WITH THE APPROACHING SHORTWAVE...SO WILL FORECAST A SLIGHT CHANCE OR CHANCE OF THUNDERSTORMS ESPECIALLY GIVEN MLCAPE IN THE LOWEST KM OF 500 TO 800J/KG. HIGHS 80 TO 85 MONDAY LEANING TOWARD THE COOLER GUIDANCE GIVEN EXPECTED CLOUD COVER...WITH OVERNIGHT LOWS MONDAY NIGHT IN THE 60S. FOR THE PERIOD TUESDAY THROUGH FRIDAY...BROAD TROUGHING ALOFT IS FORECAST BY BOTH THE ECMWF AND GFS INTO THURSDAY...THEN DIFFERENCES BECOME SOMEWHAT PRONOUNCED WITH THE ECMWF MAINTAINING THE BROAD TROUGHING...WHILE THE GFS FORECASTS AN INCREASE IN MID-LEVEL VORTICITY MOVING NORTH ALONG THE CAROLINA COAST FOR THE END OF THE WEEK. THE ECMWF ALSO HAS AN INCREASE IN THE MID-LEVEL VORTICITY FOR THE END OF THE WEEK BUT MUCH MORE OFFSHORE. ON BOTH MODELS...SURFACE HIGH PRESSURE DOMINATES. COARSE MODEL SOUNDINGS FROM THE ECMWF ARE CAPPED FOR MUCH OF THIS PERIOD...AND EVEN THE COARSE MODEL SOUNDINGS FROM THE GFS INDICATE A MOSTLY CAPPED...STABLE AIR MASS. WHILE THE 12/12Z ECMWF PROVIDED FOR AN INCREASE IN MEAN RELATIVE HUMIDITY FRIDAY...AND ITS COARSE MODEL SOUNDINGS SUGGESTED THE POTENTIAL FOR AN ISOLATED THUNDERSTORM PARTICULARLY OVER THE WESTERN PIEDMONT FRIDAY AFTERNOON AND EVENING...ITS MEE MOS GUIDANCE MEAN POPS WERE WELL BELOW CLIMATOLOGY. A LITTLE CONCERNED ABOUT THE HIGH POPS OF THE GFS ON THURSDAY...BUT ITS COARSE MODEL SOUNDINGS...WITH THE MID- LEVELS DRY IN MOST LOCATIONS...SUGGEST FOR NOW LIGHT PRECIPITATION IF ANY OCCURS. HOWEVER...THE LATEST ECMWF HAS TRENDED WETTER AND IS AT LEAST SIMILAR TO THE GFS THURSDAY WITH DEEPENING LOW PRESSURE ALOFT. WITH A CHANCE OF SHOWERS MAINLY OVER EAST PARTS OF CENTRAL NORTH CAROLINA TUESDAY MORNING BEHIND DEPARTING LOW PRESSURE...FOR THIS FORECAST PLAN TO HAVE CHANCES BELOW SLIGHT FOR THE MUCH OF THE FORECAST PERIOD BEYOND THEN...MAINTAINING A SLIGHT CHANCE OF SHOWERS THURSDAY IN DEFERENCE TO THE GFS AND THE LATEST ECMWF. IF THE TREND OF THE ECMWF CONTINUES...SMALL CHANCES OF SHOWERS MAY NEED TO BE REINTRODUCED TO THE FORECAST ON WEDNESDAY AND FRIDAY. 1000-850MB THICKNESSES TUESDAY WOULD SUGGEST HIGHS CLOSER TO THE MEAN MOS GUIDANCE OF THE ECMWF...OR AROUND 80 DEGREES...PROVIDED CLEARING OCCURS IN THE WAKE OF LOW PRESSURE. FOR THE REST OF THE WORK WEEK...AS SURFACE HIGH PRESSURE BUILDS IN...THICKNESSES SUGGEST HIGHS IN THE 70S. MANY AREAS SHOULD NOTE OVERNIGHT LOWS IN THE 50S. && .AVIATION /12Z FRIDAY THROUGH WEDNESDAY/... AS OF 735 AM SATURDAY... CONTINUED UNSETTLED WEATHER AND ADVERSE AVIATION CONDITIONS ARE EXPECTED AS A FRONT REMAINS NEAR/OVER THE AREA. CURRENTLY A WAVE OF LOW PRESSURE MOVING ALONG THE FRONT IS TRIGGERING AN AREA OF SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE WESTERN PORTIONS OF THE FORECAST AREA. THESE ARE PROGRESSING EAST AND LATEST INDICATIONS ARE THEY WILL HOLD TOGETHER. REGARDLESS OF ANY PRECIP...CIGS/VSBYS WILL REMAIN IN THE IFR/LIFR RANGE THROUGH MORNING HOURS. AS THIS WAVE CONTINUES ALONG THE FRONT AND ADDITIONALLY AS ANOTHER REINFORCING FRONT APPROACHES FROM THE NORTHWEST LATER TODAY...MORE NUMEROUS SHOWERS AND THUNDERSTORMS WILL DEVELOP...WITH THE BEST PRECIP CHANCES BEING FROM KRDU TO THE SOUTH AND EAST. ALTHOUGH CONFIDENCE IS NOT THAT HIGH...CIGS MAY SEE SOME IMPROVEMENT DURING THE DAY BEFORE FALLING BACK TO IFR OR LOWER ON SATURDAY NIGHT. OUTLOOK...LOW CLOUDS AND LIGHT RAIN AND/OR DRIZZLE WILL PERSIST ACROSS THE REGION THROUGH AT LEAST EARLY NEXT WEEK AS A PERIOD OF COLD AIR DAMMING COMMENCES. THE NEARLY STATIONARY FRONT SHOULD FINALLY SHIFT SOUTHEAST OF THE AREA LATE SUNDAY NIGHT INTO MONDAY...ALLOWING A GRADUAL RETURN TO BETTER AVIATION CONDITIONS. && .RAH WATCHES/WARNINGS/ADVISORIES... FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR NCZ038-039-042-043- 073>078-083>086-088-089. && $$ SYNOPSIS...BLS NEAR TERM...KRD/BLS SHORT TERM...KRD LONG TERM...DJF AVIATION...KRD

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