Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301625 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1225 PM EDT TUE SEP 30 2014 .SYNOPSIS...WEAK HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH THROUGH THURSDAY. A STRONG COLD FRONT WILL CROSS THE CAROLINAS FROM THE WEST LATE FRIDAY AND EARLY SATURDAY. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... AS OF 1230 PM TUESDAY... THROUGH TONIGHT: EXPECT LOW STRATUS TO GRADUALLY MIX OUT THIS AFTERNOON AS VERTICAL MIXING INCREASES IN ASSOC/W INSOLATION. EXPECT HIGHS REBOUNDING INTO THE UPPER 70S TO LOWER 80S AS LONG AS CLOUD COVER SCATTERS OUT BY ~18Z. AN UPPER LEVEL LOW DIGGING ACROSS THE LOWER GREAT LAKES TODAY WILL PROGRESS ACROSS THE MID-ATLANTIC NEAR OR JUST NORTH OF THE MASON DIXON LINE TONIGHT. UPPER LEVEL FORCING (AND PRECIPITATION POTENTIAL) ASSOC/W THIS FEATURE SHOULD LARGELY REMAIN NORTH OF CENTRAL NC...THOUGH A PERIOD OF CLOUD COVER AND PERHAPS AN ISOLD SHOWER COULD NOT BE ENTIRELY RULED OUT BETWEEN 00- 06Z WED IN THE N/NW PIEDMONT. EXPECT LOWS IN THE UPPER 50S TO NEAR 60F. WED/WED NIGHT: COMPLEX PATTERN IN THIS PERIOD WITH A NON-ZERO CHANCE FOR PRECIPITATION. THE UPPER LOW PROGRESSING THROUGH THE MID- ATLANTIC TONIGHT WILL MOVE OFFSHORE THE MID-ATLANTIC COAST ON WED AS A SHORTWAVE RIDGE BUILDS OVER THE TN/OH VALLEY. SMALL AMPLITUDE WAVES DIGGING SE INTO VA ON THE WESTERN PERIPHERY OF THE EXITING UPPER LOW ON WED COULD PERHAPS PROVIDE A GLANCING BOUT OF DPVA DURING THE DAY...OTHERWISE...ONE WOULD EXPECT SUBSIDENCE TO GRADUALLY TAKE HOLD LATE WED INTO WED NIGHT AS THE SHORTWAVE RIDGE PROGRESSES TO THE SPINE OF THE APPALACHIANS. BOTH THE GFS/NAM DEVELOP VERY LIGHT PRECIP OVER THE NORTHERN PIEDMONT WED...WHILE THE NAM GENERATES ADDITIONAL PRECIP WED NIGHT. IT IS DIFFICULT TO ASCERTAIN WHY MODEL GUIDANCE IS DEVELOPING PRECIPITATION WED/WED NIGHT...ESP WITH WEAK LOW-LEVEL FLOW AND MARGINAL/SHALLOW INSTABILITY (EQUILIBRIUM LEVEL ~10 KFT). AT THIS TIME WILL CONTINUE TO INDICATE A DRY FCST. HIGHS WED SLIGHTLY WARMER THAN TODAY...IN THE LOWER 80S. LOWS WED NIGHT IN THE UPPER 50S/LOWER 60S. -VINCENT && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 1230 PM TUESDAY... TO BE UPDATED SOON. && .LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 300 AM TUESDAY... FOR THE PERIOD FRIDAY THROUGH TUESDAY...THE ECMWF AND THE GFS CONTINUE TO BE IN FAIRLY GOOD AGREEMENT WITH THE TIMING OF AN ELONGATED MID-LEVEL SHORTWAVE MOVING INTO CENTRAL NORTH CAROLINA BY 00Z SATURDAY AND THEN EAST OF THE AREA BY 12Z SATURDAY. ONE TREND HAS BEEN FOR THE MID-LEVEL RIDGE TO BE SLIGHTLY MORE AMPLIFIED... WHICH...IF THE TREND CONTINUES...COULD SLOW THE ONSET OF ANY SHOWERS OR THUNDERSTORMS DURING THE DAY FRIDAY. LAPSE RATES ON COARSE GFS AND ECMWF MODEL SOUNDINGS ARE NEAR MOIST ADIABATIC AT BEST...SO INSTABILITY SHOULD BE LIMITED. STILL...WITH WINDS OFF OF THE SURFACE INCREASING TO AT OR A LITTLE ABOVE 30KT AHEAD OF THE COLD FRONT... CURRENT THINKING IS THAT ANY STRONGER STORM COULD HAVE A GUSTY WIND...THOUGH NOT CONFIDENT CURRENTLY IN THE PROBABILITY OF ISOLATED SEVERE WEATHER GIVEN THE MARGINAL LAPSE RATES. DRY CONDITIONS WILL BE FORECAST SATURDAY THROUGH SUNDAY...THOUGH THE ECMWF DOES CONTINUE TO FORECAST GREATER DIGGING WITH UPPER-LEVEL LOW PRESSURE MOVING THROUGH THE OHIO VALLEY AND EAST ACROSS AREAS JUST NORTH OF CENTRAL NORTH CAROLINA SATURDAY NIGHT. AGAIN...THE TREND OF THIS WILL NEED TO BE WATCHED...BUT CURRENTLY THE MID-LEVEL MOISTURE ASSOCIATED WITH THE UPPER LOW ON THE ECMWF STAYS NORTH OF CENTRAL NORTH CAROLINA SATURDAY NIGHT INTO EARLY SUNDAY. BEHIND THE COLD FRONT ON SATURDAY OR SATURDAY NIGHT...HOWEVER...SOME JET STREAK CIRRUS COULD OCCUR IF THE GFS AND ECMWF UPPER-LEVEL MOISTURE FORECASTS VERIFY IN CONJUNCTION WITH THE JET AXIS ALOFT. THE ECMWF IS ALSO MORE AMPLIFIED WITH ANOTHER IN A SERIES OF MID- LEVEL WAVES IN THE NORTHWEST FLOW...THIS ONE APPROACHING THE SOUTHERN APPALACHIANS MONDAY. THE GFS IS DRY WITH LITTLE FORCING... WHILE THE ECMWF HAS MORE OF A SURFACE REFLECTION WITH THE MID-LEVEL WAVE AND ENOUGH MID-LEVEL MOISTURE FOR LIGHT PRECIPITATION OVER THE WESTERN AND NORTHWEST PIEDMONT LATE MONDAY AFTERNOON OR MONDAY NIGHT. WITH SURFACE HIGH PRESSURE OVER THE GULF...IF THERE IS ANY PRECIPITATION MONDAY...THE THOUGHT IS IT WOULD BE MID-LEVEL DRIVEN AND MOSTLY LIGHT. FOR THIS FORECAST WILL TREND A LITTLE MORE PESSIMISTIC ON THE LAST DAY OF THE LONG-TERM PERIOD...INCREASING CLOUDS BUT KEEPING THE OVERALL FORECAST DRY. AFTER HIGHS IN THE MID 70S TO NEAR 80 FRIDAY AHEAD OF THE FRONT... BY SATURDAY NIGHT...AS THE GUIDANCE STILL SHOWS CHILLY 1000-850MB THICKNESSES INTO THE 1340S...THERE SHOULD BE AT LEAST A FEW 40S OVER THE WESTERN AND NORTHERN PIEDMONT. MODEST WARMING FOR THE END OF THE WEEKEND AND THE START OF NEXT WEEK. HIGHS SHOULD BE BACK AT LEAST IN THE LOWER TO MID 70S FOR MONDAY. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 1200 PM TUESDAY... 24-HR TAF PERIOD: IFR/LIFR CEILINGS WILL GRADUALLY MIX OUT TO MVFR BETWEEN 15-18Z...WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THIS AFTERNOON AND EVENING. THE LATEST MODEL GUIDANCE SUGGESTS THAT A REPEAT OF WIDESPREAD FOG AND LOW CEILINGS IS UNLIKELY TONIGHT... THOUGH EASTERN PORTIONS OF THE AREA (I.E. RDU/FAY/RWI) COULD SEE A PERIOD OF FOG BETWEEN 08-12Z WED MORNING. LOOKING AHEAD: VFR CONDITIONS ARE EXPECTED TO PREVAIL WED AS WEAK HIGH PRESSURE EXTENDS INTO THE REGION FROM THE NORTH. MVFR/IFR CEILINGS MAY DEVELOP EARLY THURSDAY MORNING AS HIGH PRESSURE BEGINS TO SHIFT OFF THE EASTERN SEABOARD. OTHERWISE...THE NEXT CHANCE FOR ADVERSE AVIATION CONDITIONS WILL BE LATE FRI AND EARLY SAT AS A STRONG COLD FRONT CROSSES THE CAROLINAS FROM THE WEST. -VINCENT && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...HARTFIELD LONG TERM...DJF AVIATION...VINCENT

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