Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301348 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 948 AM 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 TONIGHT/... AS OF 945 AM TUESDAY... DENSE FOG HAS BEGUN TO LIFT INTO A LOW-OVERCAST ACROSS CENTRAL NC AS OF 930 AM THIS MORNING...AND THE DENSE FOG ADVISORY HAS BEEN CANCELLED. EXPECT LOW STRATUS TO GRADUALLY MIX OUT LATE THIS MORNING THROUGH EARLY THIS AFTERNOON GIVEN LITTLE OR NO ADVECTION AND WEAK VERTICAL MIXING ASIDE FROM THAT WHICH ARISES FROM INCREASING INSOLATION. EXPECT HIGHS REBOUNDING INTO THE UPPER 70S TO LOWER 80S AS LONG AS CLOUD COVER SCATTERS OUT BY ~18Z. SHORTWAVE ENERGY 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 ANY POTENTIAL FOR PRECIPITATION) ASSOC/W THIS FEATURE WILL 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. -VINCENT && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 245 AM TUESDAY... AS NOTED ABOVE... WE SHOULD SEE AT LEAST SOME SCATTERED CLOUDS MAINLY OVER THE EAST WED MORNING. THE PRESENCE OR LACK OF SUCH CLOUDS WILL IMPACT HOW MUCH FOG FORMS WED MORNING. WE SHOULD SEE AT LEAST SOME LIGHT FOG TO START THE DAY... AND PERHAPS MORE DENSE IF THE AFOREMENTIONED CLIPPER-ASSOCIATED CLOUDS DO NOT HAPPEN. OTHERWISE... EXPECT A PARTLY TO MOSTLY SUNNY DAY. THE CLIPPER LOW WILL CROSS NEW ENGLAND AS THE STRONG VORTICITY MAX ROUNDS ITS BASE... SHIFTING OFF THE NJ COAST... AND WE SHOULD SEE A BIT MORE FLAT DAYTIME CUMULUS FROM THE TRIANGLE NORTH AND EAST CLOSER TO THE LOW. MODELS SHOW WEAK MID LEVEL RIDGING PUSHING IN FROM THE WEST LATE... BETWEEN THE DEPARTING CLIPPER AND A DEEPENING TROUGH COVERING THE EASTERN ROCKIES AND HIGH PLAINS LATE WED/WED NIGHT. WHILE MODELS SHOW A MINOR PERTURBATION TRACKING EASTWARD OVER THE SOUTHEAST STATES WED NIGHT... THIS SHOULD BE OF LITTLE CONSEQUENCE WITH DEEP DRY AIR MOVING IN. EXPECT DRY WEATHER THROUGH WED NIGHT. THICKNESSES ARE EXPECTED TO START WED ABOUT 10 M ABOVE NORMAL... SUPPORTING HIGHS ABOUT A CATEGORY ABOVE NORMAL... 80-84. SOME CLOUDINESS POSSIBLE WED NIGHT ESPECIALLY OVER THE WEST WHERE MODELS INDICATE AN UPTICK IN LOW LEVEL MOISTURE TRANSPORT GENERATED BY LIGHT BUT CONFLUENT AND UPSLOPE-DIRECTED LOW LEVEL FLOW. LOWS WITHIN A COUPLE DEGREES OF 60. -GIH && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 300 AM TUESDAY... FOR THE PERIOD THURSDAY THROUGH THURSDAY NIGHT...A MID-LEVEL RIDGE AXIS BUILDS INTO CENTRAL NORTH CAROLINA THURSDAY...WITH THE AXIS MOVING EAST THURSDAY NIGHT. THE GUIDANCE HAS CONTINUED TO FORECAST VERY MINOR QPF IN CENTRAL NORTH CAROLINA DURING THIS PERIOD...WITH THE GFS FORECASTING THIS THURSDAY AND THE NAM MORE THURSDAY NIGHT. THE GFS DOES HAVE A RELATIVE MAXIMUM OF 850MB THETA-E AIR OVER CENTRAL NORTH CAROLINA THURSDAY WITH WEAK 850MB LIFT...BUT HEIGHTS ALOFT ARE RISING AND ANY LOW-LEVEL FORCING WITH ANY SURFACE BOUNDARY SHOULD BE WEAK. LIFTED INDICES ARE ABOVE 0C...AND MLCAPE IN THE LOWEST KM DOES NOT REGISTER AS BUFR SOUNDINGS FROM BOTH THE NAM AND GFS APPEAR CAPPED. GIVEN THE ORIENTATION OF 1000-500MB THICKNESSES...POSSIBLY A SHOWER COULD DRIFT SOUTHEAST FOLLOWING THE THERMAL WIND FROM HIGHER TERRAIN AND GET CLOSE TO THE NORTHWEST PIEDMONT THURSDAY AFTERNOON OR EVENING...BUT GIVEN THE UNCERTAINTY WILL KEEP THE FORECAST DRY. MOS GUIDANCE POPS ARE IN SINGLE FIGURES IN BOTH THE MAV AND THE MET. WITH AT LEAST A PARTLY SUNNY SKY EXPECTED...1000-850MB THICKNESSES WOULD SUGGEST LOWER TO MID 80S FOR HIGHS...IN CONJUNCTION WITH MAV AND MET MOS GUIDANCE. OVERNIGHT LOWS THURSDAY NIGHT NEAR 60 IN THE NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN UNDERNEATH THE RIDGE AXIS ALOFT FOR A GOOD PART OF THE NIGHT...LOWER 60S ELSEWHERE AND POSSIBLY ON THE HIGHER END OF THE LOWER 60S TOWARD THE TRIAD AS THE WINDS OFF OF THE SURFACE START TO INCREASE OVERNIGHT. 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 945 AM 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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