Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 131849 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 245 PM EDT SAT SEP 13 2014 .SYNOPSIS...A COLD FRONT WILL PUSH SOUTH THROUGH THE AREA TONIGHT...AS HIGH PRESSURE BUILDS INTO THE AREA FROM THE NORTH. THE FRONTAL ZONE WILL CONTINUE TO LINGER OVER THE REGION THROUGH MIDWEEK...LEADING TO CONTINUED UNSETTLED WEATHER. && .NEAR TERM /THROUGH SUNDAY/... AS OF 245 PM SATURDAY... ...FLASH FLOOD WATCH REMAINS IN EFFECT ACROSS THE SOUTHERN PIEDMONT... SANDHILLS... AND SE COASTAL PLAIN AS HEAVY RAIN REMAINS A CONCERN THROUGH EARLY SUNDAY... STRATUS...WHILE LIFTING A BIT...HAS HELD ON STRONG OVER THE NORTHERN HALF OF THE AREA. THE WEAK WARM FRONT THAT MOVED IN FROM THE SOUTH AND COLD FRONT FROM THE NORTHWEST HAVE ESSENTIALLY MERGED AND CREATED ONE AXIS OF CONVERGENCE STRETCHING FROM THE SOUTHERN PIEDMONT TO THE NORTHERN COASTAL PLAIN. ALONG AND SOUTH OF THIS BOUNDARY...SCATTERED SHOWERS AND STORMS ARE DEVELOPING IN AN AIRMASS CHARACTERIZED BY MLCAPE OF 500-1500 J/KG AND PW OVER 2 INCHES. WIND FIELDS ARE WEAK WELL SOUTH OF THE MAIN JET OVER THE OHIO VALLEY..SO THE MAIN IMPACTS TODAY WILL BE LOCALLY HEAVY RAINFALL FROM SLOW MOVING/TRAINING CELLS. DUE IN PART TO THE LIMITED HEATING ACROSS THE NORTH...HI-RES GUIDANCE HAS TRENDED SOUTH WITH THE MAIN AREA OF CONVECTION AND HEAVY RAIN POTENTIAL...WITH THE FOCUS NOW FROM THE ANSON COUNTY EAST TOWARD WAYNE/WILSON COUNTIES. GIVEN THESE MODEL TRENDS AND DEVELOPING NORTHWESTERLY FLOW BEHIND THE AFOREMENTIONED BOUNDARY...WE REMOVED DAVIDSON AND RANDOLPH COUNTIES FROM THE FLASH FLOOD WATCH EARLIER THIS AFTERNOON. CURRENTLY FEEL THE SWEET SPOT OF FLOODING POTENTIAL WILL BE ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN...BUT WILL LEAVE THE REMAINDER OF THE WATCH AS IS BASED ON CURRENT RADAR TRENDS ACROSS THE SOUTH. TONIGHT...HIGH PRESSURE WILL BUILD IN FROM THE NORTH AND PUSH THE COLD FRONT SOUTH OF OUR CWA. MODELS SHOW SOME WEAK ISENTROPIC LIFT ALONG THE FRONT AS IT MAKES ITS STRONGER PUSH TO THE SOUTH LATE TONIGHT...WHICH EXPANDS ACROSS THE WESTERN PIEDMONT BY SUNDAY MORNING. FROM THIS THERE MAY BE SOME PATCHY DRIZZLE DEVELOP AS LOWER STRATUS DEVELOPS. AT THE SAME TIME...MUCH DRIER ARI WILL BE FILTERING IN FROM THE NORTH...SO ANY DRIZZLE SHOULD STAY MOSTLY CONFINED TO SOUTHERN AREAS. LOWS IN THE LOW TO MID 60S. SUNDAY...NOT MUCH IN THE WAY OF FORCING FOR PRECIP AS THE MORNING ISENTROPIC UPGLIDE RELAXES AND WE ARE LEFT WITH JUST LOW CLOUDS THAT SHOULD LIFT A BIT DURING THE AFTERNOON. WILL MAINTAIN A SMALL CHANCE OF PRECIP ACROSS THE SOUTH...BUT TRENDS HAVE BEEN TOWARD LESS AND LESS POTENTIAL. HIGHS WILL BE MUCH COOLER WITH THE SURFACE RIDGE OVER THE AREA AND OVERCAST SKIES...BUT NO PRECIP EXPECTED...READINGS SHOULD BE ABLE TO REACH THE LOWER 70S NORTHWEST TO UPPER 70S 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 /18Z FRIDAY THROUGH THURSDAY/... AS OF 145 PM SATURDAY... LOW CEILINGS CONTINUE INTO THE AFTERNOON ACROSS MOST OF CENTRAL NC...THOUGH THERE ARE SOME SIGNS OF SCATTERING OVER THE SOUTHERN AND WESTERN PIEDMONT AS A COLD FRONT MOVES INTO THE AREA FROM THE WEST. HOWEVER... THERE IS STILL A LOT OF LOW-LEVEL MOISTURE AND AT LEAST MVFR CEILINGS MAY PERSIST WELL INTO THE EVENING. SCATTERED TO NUMEROUS SHOWERS AND STORMS ARE EXPECTED TO DEVELOP ALONG AND SOUTHEAST OF THE FRONTAL ZONE...WHICH IS MAINLY FROM KRDU TO KRWI/KFAY BETWEEN ROUGHLY 19Z AND 03Z. SOME OF THE STORMS MAY BE VERY HEAVY AND PRODUCE LIFR CONDITIONS AND A WIND GUSTS OF 20-30KT. TONIGHT...HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE NORTH AS THE FRONT AND MOST OF THE PRECIP PUSHES SOUTH OF THE AREA. FORECAST SOUNDINGS SHOW MOSTLY MVFR CEILINGS...BUT THERE MAY BE SOME IFR CEILINGS/VSBYS AND PATCHY LIGHT RAIN/DRIZZLE AROUND KFAY BEHIND THE FRONT. LOW CLOUDS WILL THEN LIKELY PERSIST WELL INTO THE DAY ON SUNDAY. 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 NCZ042-043-073>078-083>086-088-089. && $$ SYNOPSIS...BLS NEAR TERM...BLS SHORT TERM...KRD LONG TERM...DJF AVIATION...KRD/BLS

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