Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 010140 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 930 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 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 /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 800 PM TUESDAY... HIGH PRESSURE OVER THE AREA HAS LEAD TO MOSTLY CLEAR SKIES THIS EVENING. IN ADDITION...WINDS WILL BECOME MOSTLY CALM OVER THE NEXT COUPLE OF HOURS. THESE CLEAR SKIES AND LIGHT/CALM WINDS SHOULD LEAD TO ANOTHER NIGHT OF FOG. HOWEVER...IT IS NOT A SURE BET AS MODELS ARE IN DISAGREEMENT (WITH ONE SHOWING PREDOMINATELY VFR CONDITIONS ALL NIGHT). NEVERTHELESS... GIVEN A SIMILAR SET UP TO LAST NIGHT (MINUS THE LIGHT RAIN THAT OCCURRED ON MONDAY)...WENT AHEAD AND INCLUDED IFR/LIFR VSBYS/CIGS IN ALL TAF SITES EXCEPT THE TRIAD WHERE THERE IS SLIGHTLY DRIER AIR (BUT STILL INCLUDED SOME SUB-VFR CONDITIONS). CONDITIONS SHOULD IMPROVE TO VFR BY THE MID MORNING HOURS OF WEDNESDAY...WITH JUST SOME MID/HIGH CLOUDS AND LIGHT AND VARIABLE WINDS FOR THE REMAINDER OF THE TAF PERIOD GIVEN THE HIGH PRESSURE OVERHEAD. OUTLOOK...VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH LATE WEDNESDAY/EARLY THURSDAY MORNING AS WEAK HIGH PRESSURE EXTENDS INTO THE REGION FROM THE NORTH. MVFR/IFR CIGS/VSBYS MAY DEVELOP EARLY THURSDAY MORNING AS THE HIGH BEGINS TO SHIFT OFFSHORE. 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. && $$ SYNOPSIS...VINCENT NEAR TERM...PWB SHORT TERM...VINCENT/CBL LONG TERM...CBL AVIATION...KRD/VINCENT

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