Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 010525 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 125 AM EDT WED OCT 01 2014 .SYNOPSIS...WEAK HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE NORTH TODAY THROUGH THURSDAY. A COLD FRONT WILL APPROACH FROM THE WEST LATE FRIDAY... AND SWEEP EAST THROUGH THE AREA FRIDAY NIGHT INTO SATURDAY MORNING. COOL HIGH PRESSURE WILL PUSH IN FROM THE WEST SATURDAY AFTERNOON THROUGH SUNDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 930 PM TUESDAY... THE PROBLEM OF THE NIGHT WILL BE THE LIKELIHOOD OF FOG DEVELOPMENT AGAIN OVER THE NE PIEDMONT AND N COASTAL PLAIN... AGAIN POTENTIALLY DENSE. IT TOOK MUCH OF THE DAY TO DISSOLVE THE STRATUS LAYER OVER A GOOD PORTION OF THE NORTHEAST PIEDMONT INTO THE CENTRAL PIEDMONT. THE END RESULT WAS LITTLE IN THE WAY OF EVAPORATION OF TOP SOIL MOISTURE THIS AFTERNOON IN THIS REGION. DEW POINTS FAILED TO MIX OUT AND DRY AND WERE STILL IN THE LOWER 60S IN THESE AREAS THIS EVENING. THERE HAS BEEN A RAPID LOW LEVEL INVERSION SET UP THIS EVENING WITH THE LINGERING MOIST BOUNDARY LAYER... CLEAR SKIES... AND STRONG DIURNAL TEMP FALL WITH SUNSET. THIS IS ESPECIALLY EVIDENT AT MID-EVENING FROM ROXBORO AND RALEIGH TO ROCKY MOUNT AND HALIFAX. THERE ARE REPORTS OF FOG ALREADY IN THIS REGION... SOME LOCALLY BECOMING DENSE (1/4 MILE VSBY OR LESS). WITH THE TEMP/DEW POINT TEMP SPREAD ALREADY LESS THAN 3 DEGREES... FOG APPEARS INEVITABLE. ELSEWHERE... AFTERNOON SUN LED TO SOME DECENT EVAPORATION AND LED TO HIGHS AROUND 80. THERE WAS ENOUGH MIXING IN THAT THE LOW LEVEL INVERSION WAS SLOWER TO SET UP FROM GREENSBORO AND SOUTH AND WEST. BOTTOM LINE... FOG SHOULD DEVELOP OVERNIGHT. AREAS OF DENSE FOG WILL BE POSSIBLE AGAIN ESPECIALLY FROM ROXBORO AND RALEIGH NORTH AND EAST TO ROCKY MOUNT AND ROANOKE RAPIDS. A DENSE FOG ADVISORY MAY BE NEEDED LATER IF THE DENSE FOG IS THOUGHT TO BECOME WIDESPREAD TO BECOME A HAZARD TO EARLY MORNING COMMUTERS. FOR NOW... WE WILL TREND TOWARD THAT SCENARIO BY PLACING AREAS OF FOG IN THE FORECAST. OTHERWISE... MOSTLY CLEAR. PATCHY FOG ELSEWHERE. LOWS 55-60 WEST AND LOWER 60S EAST AND SOUTH. FOG SHOULD LIFT AS A STATUS DECK OF CLOUDS AGAIN WED... AND MAY LINGER AGAIN UNTIL LATE MORNING IN THE NE ZONES. -PWB && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... AS OF 235 PM TUESDAY... 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 THURSDAY AND THURSDAY NIGHT: SYNOPTIC SCALE SUBSIDENCE WILL PREVAIL ACROSS CENTRAL NC ON THURSDAY AS HEIGHTS INCREASE OVER THE AREA...DOWNSTREAM OF THE SOUTHERN STREAM TROUGH EJECTING EASTWARD OUT OF THE CENTRAL/SOUTHERN ROCKIES...PROGRESSING EASTWARD INTO THE SOUTHERN PLAINS/LOWER MS VALLEY THURSDAY NIGHT. IF CURRENT TIMING HOLDS UP...IT SHOULD REMAIN DRY THROUGH THURSDAY NIGHT AS GFS BUFR SOUNDINGS REMAIN STRONGLY CAPPED ALOFT...WITH STRENGTHENING SOUTHERLY RETURN FLOW LEADING TO AN INCREASE IN CLOUDS FROM WEST- EAST. HIGHS 80 TO 85. LOWS IN THE LOWER TO MID 60S. FRIDAY AND FRIDAY NIGHT: MODELS INDICATE PHASING NORTHERN STREAM AND SOUTHERN STREAM TROUGHS ACROSS THE UPPER MS VALLEY/UPR MIDWEST AND INTO THE GREAT LAKES FRIDAY AND FRIDAY NIGHT. MODELS ARE IN REALLY GOOD AGREEMENT WITH THE TIMING OF THE ACCOMPANYING COLD FRONT PASSAGE INTO THE AREA LATE FRIDAY AFTERNOON/FRIDAY EVENING...EXITING EASTERN PORTIONS OF THE FORECAST AREA BY DAYBREAK SATURDAY. THE LEAD SOUTHERN STREAM WAVE OVER THE LOWER MS VALLEY/TN VALLEY FRIDAY MORNING REALLY SHEARS OUT/DAMPENS AS IT LIFTS NORTHWARD INTO MID- ATLANTIC REGION FRIDAY EVENING/NIGHT...RESULTING IN WEAK UPPER LEVEL SUPPORT WITH EASTWARD ADVANCING 30-35KT SWLY LLJ FOCUSING STRONG MOISTURE TRANSPORT AND LOW-LEVEL CONVERGENCE WITHIN A BAND OF CONVECTION ALONG THE FRONT. LATE DIURNAL TIMING AND MODEST LAPSE RATES ALOFT WILL RESULT IN LIMITED/WEAK INSTABILITY(200-400 MUCAPE)...THWARTING ANY SEVERE THREAT. HAVE INCREASED POPS TO LIKELY ACROSS THE FORECAST AREA FRIDAY NIGHT...DECREASING WEST TO EAST DURING THE PREDAWN HOURS AS FRONT MOVES EASTWARD TOWARDS THE COAST. PROGRESSIVE NATURE OF SYSTEM WILL LIMIT RAINFALL AMOUNTS...WITH AVERAGE QPF AMOUNTS OF A 0.25-0.50". MAX TEMPS FRIDAY AFTERNOON WILL DEPEND ON ARRIVAL/ONSET OF SHOWERS/CONVECTION...ESPECIALLY IN THE WEST. UNDER THICKENING CLOUD COVER...A BIT COOLER THAN THURSDAY RANGING FROM MID 70S WEST TO LOWER 80S EAST. MIN TEMPS WILL DEPEND ON WEST-EAST TIMING OF FROPA FRIDAY NIGHT THROUGH THE AREA...RANGING FROM LOWER/MID 50S NORTHWEST TO LOWER/MID 60S SE. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 235 PM TUESDAY... IN THE WAKE OF THE FRONTAL PASSAGE SATURDAY MORNING...DRY CONDITIONS WILL PREVAIL THROUGH EARLY NEXT WEEK AS SFC HIGH PRESSURE OVER THE SOUTHERN PLAINS/LOWER MS VALLEY BUILDS EAST THROUGH THE PERIOD...SHIFTING EAST OFF THE SOUTHEAST COAST ON MONDAY. AFTER A CHILLY SATURDAY NIGHT/SUNDAY MORNING IN WHICH FAVORABLE RADIATIONAL CONDITIONS WILL HELP SUPPORT MIN TEMPS IN THE MID TO UPPER 40S ACROSS A LARGE PORTION OF THE FORECAST AREA...TEMPERATURES WILL MODERATE TO NEAR NORMAL BY MONDAY. TIMING/MAGNITUDE OF THE NEXT SYSTEM STILL IN QUESTION AS NORTHERN STREAM ENERGY ROTATING SOUTHEASTWARD THROUGH THE BASE OF THE AMPLIFIED TROUGH LOOKS TO IMPACT THE REGION LATE MONDAY-TUESDAY TIME FRAME. UNTIL MODEL DISCREPANCIES CAN BE IRONED OUT WITH THIS CLIPPER- LIKE TROUGH...WILL INDICATE CONSERVATIVE/SLIGHT CHANCE POPS...ESPECIALLY GIVEN POTENTIAL FOR LIMITED MOISTURE AVAILABILITY. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 125 AM WEDNESDAY... CHANCES ARE GOOD FOR IFR/LIFR CONDITIONS AT RDU/RWI/FAY UNTIL MID MORNING. THE COMBINATION OF MOSTLY CLEAR SKIES AND CALM WINDS HAS PROMPTED FORMATION OF AREAS OF FOG... DENSE IN SPOTS. THIS FOG IS EXPECTED TO FILL IN ACROSS MUCH OF CENTRAL AND ERN NC OVER THE NEXT FEW HOURS... HOLDING THROUGH 14Z OR 15Z BEFORE SLOWLY DISPERSING. THERE IS MUCH MORE UNCERTAINTY AT INT/GSO... WHERE FOG IS CURRENTLY LIGHT/PATCHY... AND HIGH-RES MODEL OUTPUT PLACES THE WESTERN EDGE OF THE FOG/STRATUS JUST EAST OF THE TRIAD AREA. WILL HAVE SCTD LOW STRATUS AND LIGHTER FOG AT INT/GSO... WHILE AT RDU/RWI/FAY... WILL INDICATE LIFR CIGS/VSBYS UNTIL 14Z/15Z. AFTER THIS TIME... EXPECT A TREND TO VFR CONDITIONS AT ALL CENTRAL NC TAF SITES THROUGH THE REST OF TODAY... AS WEAK HIGH PRESSURE EXTENDS OVER THE REGION. RENEWED FOG DEVELOPMENT IS EXPECTED TOWARD THE END OF THE TAF VALID PERIOD (06Z THU). SURFACE WINDS WILL STAY LIGHT/VARIABLE. LOOKING BEYOND 06Z EARLY THU MORNING... MVFR OR IFR VSBYS IN FOG MAY DEVELOP ONCE AGAIN AND AFFECT CENTRAL NC TERMINALS FROM 08Z-13Z THU MORNING. OTHERWISE... EXPECT VFR CONDITIONS THU. A FEW SPRINKLES OR SHOWERS ARE POSSIBLE MAINLY AT RWI/FAY THU AFTERNOON/EVENING... BUT SUB-VFR CONDITIONS ARE NOT EXPECTED. PATCHY FOG MAY AGAIN DEVELOP EARLY FRI MORNING. A STRONG FRONTAL SYSTEM WILL BRING INCREASING SURFACE WINDS FROM THE SW AND A GOOD CHANCE OF SUB-VFR CONDITIONS IN SHOWERS AND STORMS LATE FRI AFTERNOON THROUGH FRI NIGHT/EARLY SAT MORNING. VFR CONDITIONS SHOULD THEN RESUME SAT AFTERNOON... LASTING THROUGH SUNDAY. -GIH && $$ SYNOPSIS...HARTFIELD NEAR TERM...PWB SHORT TERM...VINCENT/CBL LONG TERM...CBL AVIATION...HARTFIELD

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