Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011852 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 250 PM EDT WED APR 1 2015 .SYNOPSIS...
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HIGH PRESSURE REMAINS OVER THE REGION INTO THURSDAY. HIGH PRESSURE DRIFTS EAST THURSDAY AND THURSDAY NIGHT...WITH A WARM SOUTHWEST FLOW FRIDAY AHEAD OF A COLD FRONT THAT SWEEPS ACROSS THE REGION FRIDAY NIGHT AND EARLY SATURDAY. HIGH PRESSURE RETURNS BY SATURDAY AFTERNOON...CONTINUING AT LEAST THROUGH SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 1125 AM WEDNESDAY... 12Z UPPER AIR ANALYSIS DEPICTS MID-UPPER LEVEL TROUGH AXIS SCOOTING EASTWARD AWAY FROM CENTRAL NC. NW FLOW AT 850MB IS ADVECTING A COOLER AIR MASS INTO OUR AREA THOUGH CORE OF COOLEST AIR WILL REMAIN TO OUR N-NE. THIS WILL SET UP A TEMPERATURE FIELD THIS AFTERNOON WITH THE COOLEST TEMPS IN THE NORTHERN COASTAL PLAIN AND WARMEST IN THE SOUTHERN PIEDMONT. SEE LITTLE NEED TO DEVIATE FROM CURRENT FORECAST OF LOW-MID 60S NE TO LOWER 70S SW. EXPECT PLENTY OF SUNSHINE THIS AFTERNOON AS SUBSIDENCE THROUGH THE COLUMN AND A DRY AIR MASS WILL DETER ANY CLOUD FORMATION (ASIDE FROM A FEW STRANDS OF CIRRUS). NE SFC WINDS 8-13 MPH WILL GRADUALLY BACK TO THE NORTH AND BECOME LIGHT AFTER 2-3 PM. -WSS SKIES WILL REMAIN CLEAR OR MOSTLY SO TONIGHT...WITH PERHAPS THE SOUTHERN FRINGE OF CIRRUS IN NW FLOW ALOFT GRAZING THE NORTHERN PIEDMONT THIS EVENING. H85-925 FLOW WILL BECOME SOUTHWESTERLY LATE TONIGHT AS THE CENTER OF THE ANTI-CYCLONE IN THAT LAYER DRIFTS OFF THE SC COAST...AND ASSOCIATED MOISTURE ADVECTION WILL CAUSE SOME STRATOCUMULUS TO DEVELOP AND CREEP TOWARD THE YADKIN BY DAYBREAK. BASED ON CURRENT AND PREVIOUS MODEL PROGS...IT IS UNLIKELY THAT THIS CLOUD COVER WILL ARRIVE SOON OR THICK ENOUGH TO HAVE A LARGE IMPACT ON OVERNIGHT TEMPERATURES. GIVEN THE RELATIVE CLEAR AND CONTINUED NEARBY PRESENCE OF THE AFOREMENTIONED SFC HIGH NEAR THE VA/NC COAST THAT GUIDANCE SUGGESTS WILL STRENGTHEN FURTHER BENEATH THE SUBSIDENT RIDGING ALOFT (TO NEAR 1028 MB)...GOOD TO EXCELLENT RADIATIONAL COOLING CONDITIONS ARE EXPECTED. PROJECTED LL THICKNESS VALUES AROUND 1345 METERS AT 12Z THU WILL SUPPORT MIDDLE 30S TO LOWER 40S...COOLEST EAST WHERE PATCHY FROST WILL BE POSSIBLE...NEARER THE CENTER OF THE SFC HIGH. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 355 AM WEDNESDAY... RETURN FLOW WILL DEVELOP AS THE PRECEDING SFC HIGH DRIFTS TOWARD BERMUDA...AND AS THE MSL PRESSURE GRADIENT TIGHTENS DOWNSTREAM OF A COLD FRONT APPROACHING FROM THE WEST - FROM THE LOWER GREAT LAKES TO THE CENTRAL PLAINS. WARMING SOUTHERLY FLOW WILL CONSEQUENTLY RESULT IN A RETURN OF TEMPERATURES IN THE 70S AREA-WIDE...EXCEPT PERHAPS OVER THE NW PIEDMONT WHERE STRATOCUMULUS CENTERED AROUND H85 (REFERENCED IN THE NEAR TERM DISCUSSION) MAY RESULT IN MOSTLY CLOUDY CONDITIONS BY AFTERNOON. THE WAA REGIME MAY ALSO SUPPORT THE MAINTENANCE OF A SHOWER OR TWO...FROM UPSTREAM TN VALLEY CONVECTION...ACROSS THE APPALACHIANS AND INTO THE WESTERN PIEDMONT DURING THE LATE AFTERNOON AND EVENING HOURS...BUT WEAK INSTABILITY AT BEST OVER CENTRAL NC SUGGESTS ANY SUCH ACTIVITY WILL BE DISSIPATING AS IT APPROACHES. THE PASSAGE OF A WARM FRONT AND ASSOCIATED THETA-E ADVECTION/ ISENTROPIC UPGLIDE THU NIGHT WILL CAUSE CLOUDS/STRATUS TO DEVELOP THROUGHOUT CENTRAL NC OVERNIGHT...WITH MILD AND BREEZY AT TIMES CONDITIONS...AND LOWS IN THE UPPER 50S TO LOWER 60S. BUFR SOUNDINGS DEPICT THE RELATIVE DEEPEST SATURATION - IN THE LOWEST 5-6 THOUSAND FT AND ENTIRELY ABOVE FREEZING - OVER THE WESTERN PIEDMONT...WHERE PATCHY LIGHT SHOWERS OR DRIZZLE WILL BE POSSIBLE AND IS SUPPORTED BY A SMATTERING OF A HUNDREDTH OR TWO OF QPF PER THE 00Z MODELS. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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AS OF 250 PM WEDNESDAY... IN THE MID-LEVELS FRIDAY...BOTH THE NAM AND THE GFS PROVIDE FOR A SHORTWAVE THAT MOVES THROUGH CENTRAL NORTH CAROLINA...STRONGER ON THE GFS AND WEAKENING AS IT MOVES THROUGH ON THE NAM. ON BOTH MODELS THE MEAN RELATIVE HUMIDITY ACTUALLY DECREASES DURING THE DAY...WITH UPPER CONVERGENCE ACTUALLY FORECAST ON THE GFS BY FRIDAY AFTERNOON AS SURFACE RIDGING BUILDS WEST BRIEFLY OVER THE EASTERN GULF. BUFR SOUNDINGS FROM BOTH THE NAM AND THE GFS SUGGEST LOW CLOUDS FRIDAY MORNING...FOLLOWED BY A FAIRLY CAPPED AIR MASS WITH JUST ENOUGH COOLING BETWEEN 850MB AND 700MB ON THE GFS BUFR SOUNDING TOWARD KRWI FRIDAY AFTERNOON THAT AN ISOLATED SHOWER OR THUNDERSTORM COULD OCCUR...AS MLCAPE IN THE LOWEST 2KM WILL BE TO 200J/KG. WILL NOT REMOVE ANY OF THE SLIGHT CHANCES FROM THE PREVIOUS FORECAST AS THE NAM BUFR SOUNDING EARLY FRIDAY MORNING NOTES SOME MID-LEVEL MOISTURE IN THE -10C TO -15C LAYER WITH THE APPROACHING SHORTWAVE TOWARD THE TRIAD...AND DESPITE A VERY DRY SUB-CLOUD LAYER RENEWED MID-LEVEL MOISTURE THERE OCCURS TOWARD 00Z SATURDAY. 925MB WINDS INCREASE TO 25 TO 35KT FRIDAY AFTERNOON...AND BOTH THE NAM AND GFS BUFR SOUNDINGS SUGGEST A FEW GUSTS FROM 35 TO 40MPH ARE POSSIBLE IN THE SOUTHWEST FLOW FRIDAY AFTERNOON. WITH DEW POINTS AT LEAST IN THE 50S...MINIMUM RELATIVE HUMIDITIES WILL BE TO NEAR 40 PERCENT. FRIDAY NIGHT INTO SATURDAY...THE GFS IS FASTER WITH THE TIMING OF THE COLD FRONT MOVING THROUGH CENTRAL NORTH CAROLINA...BUT BOTH THE GFS AND THE NAM SHOW AN INCREASE IN MOISTURE WITH THE GFS FORECASTING GOOD UPPER DIFFLUENCE FRIDAY NIGHT. THE RIGHT ENTRANCE REGION OF THE 300MB JET LAGS THE FRONT...BUT THE RIGHT ENTRANCE REGION OF THE 500MB JET DOES NOT LAG IT VERY MUCH...SUCH AS THERE SHOULD BE SUFFICIENT LIFT FOR AT LEAST SCATTERED SHOWERS. INSTABILITY DIMINISHES TOWARD CENTRAL NORTH CAROLINA WITH THE APPROACH OF THE FRONT...AS THE GFS REDUCES MLCAPE IN THE LOWEST 2KM TO NOT REGISTERING AND LIFTED INDICES ON BOTH THE NAM AND GFS ARE WARMER THAN 0C. ALSO...THE GFS 850MB THETA-E FORECAST SHOWS THE THETA-E RIDGE GETTING SQUEEZED ALONG AND AHEAD OF THE FRONT. GUIDANCE POPS ARE CURRENTLY CHANCE AND THE MEX MOS POPS HAVE TRENDED DOWNWARD...SO WILL KEEP HIGH CHANCES IN THE FORECAST AT THIS TIME FOR OVERNIGHT FRIDAY...PUSHING EAST QUICKLY SATURDAY MORNING AS THE AIR MASS DRIES AHEAD OF THE UPPER TROUGH. HEIGHT AND THICKNESS FALLS SHOULD RESULT IN LESS THAN 10F OF WARMING SATURDAY FROM LOWS FRIDAY NIGHT...FOR HIGHS FROM NEAR 60 IN THE TRIAD TO THE UPPER 60S TOWARD KFAY AND KCTZ. THICKNESS PACKING AND A TIGHT GRADIENT SHOULD RESULT IN BREEZY CONDITIONS...WITH BUFR SOUNDINGS SUGGESTIVE OF A FEW GUSTS AROUND OR JUST ABOVE 30MPH. MINIMUM RELATIVE HUMIDITIES COULD FALL BELOW 30 PERCENT...AND DEPENDING ON HOW MUCH RAIN OCCURS...SOME INCREASE IN FIRE DANGER COULD BE PRESENT THEN. SATURDAY NIGHT THROUGH WEDNESDAY...HIGH PRESSURE SHOULD BUILD OVERHEAD SATURDAY NIGHT...WITH THE SURFACE RIDGE AXIS MOVING QUICKLY EAST SUNDAY. THE COOLEST MORNING IN THIS PERIOD CERTAINLY LOOKS TO BE SUNDAY...WITH 1000-850MB THICKNESSES SUPPORTIVE OF 30S AND SOME MOS GUIDANCE TEMPERATURES JUST ABOVE FREEZING. WILL NOTE IN A COUPLE OF WEATHER GRIDS SOME PATCHY FROST EARLY SUNDAY MORNING IN COOL AIR UNDER THE HIGH...WITH A LIGHT WIND AND A LIKELY CLEAR SKY...ALTHOUGH SOME OF THE UPPER-LEVEL MOISTURE FIELDS HAVE AN INCREASE IN MOISTURE AT THAT LEVEL NOT TOO FAR AWAY AROUND 12Z SUNDAY. FOR THE REST OF THE LONG-TERM PERIOD...THE LONG-TERM GUIDANCE SEEMS CONSISTENT MOST DAYS WITH RESPECT TO A BACKING FLOW ALOFT...AND A BACKING FLOW AT THE SURFACE AS WELL WHICH SHOULD GRADUALLY BUILD MOISTURE FROM THE SOUTH AND SOUTHWEST. 1000-850MB THICKNESSES SUPPORT TEMPERATURES...BOTH HIGHS AND LOWS...INCREASING SUNDAY THROUGH WEDNESDAY...AND THE GENERAL PATTERN SUPPORTS THIS AS WELL. QPF IS PRESENT ON THE GFS AND ECMWF AS EARLY AS MONDAY...CONTINUING THROUGH THE REST OF THE LONG-TERM PERIOD. THE FLOW ALOFT BECOMES BROADLY DIFFLUENT...AND THERE ARE FORECAST MID-LEVEL SHORTWAVES MOVING THROUGH CENTRAL NORTH CAROLINA EACH DAY ON THE LONG-TERM GUIDANCE...WITH THE GFS STRONGER MONDAY AND WEDNESDAY IN THAT REGARD. THERE IS SOME DIFFERENCE CERTAINLY IN THE PROGRESS SOUTH OF THE NEXT COLD FRONT AT THE VERY END OF THIS LONG- TERM PERIOD...OTHERWISE...THERE APPEARS TO BE A LACK OF A DEFINING SURFACE FEATURE OVER CENTRAL NORTH CAROLINA FOR DEEP CONVECTION. IT MAY BE THAT DEEP CONVECTION OCCURS MORE SO BECAUSE OF GREATER INSTABILITY OVER HIGHER TERRAIN THEN DRIFTING SOUTHEAST...OR SIMILARLY FROM A SYNOPTIC BOUNDARY TO OUR NORTHWEST AND NORTH. OVERALL...SLIGHT CHANCE TO CHANCE POPS FOR CENTRAL NORTH CAROLINA MONDAY THROUGH WEDNESDAY...FOLLOWING AN EXPECTED PATTERN OF HIGHER CHANCES DIURNALLY THROUGH THE AFTERNOON AND EVENING WITH MOST OF THE HIGHER POPS ALONG AND WEST OF U.S. 1. FOR THIS FORECAST WILL HAVE MAXES IN THE 60S SUNDAY...LOWER TO MID 70S MONDAY...MID TO UPPER 70S TUESDAY...AND WITH MANY AREAS AROUND 80 WEDNESDAY. OVERNIGHT LOWS WILL GRADUALLY WARM AS WELL...WITH THE FORECAST FOR NOW VERY CLOSE TO RECORD HIGH MINIMUMS NEAR THE TRIAD TUESDAY NIGHT.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 100 PM WEDNESDAY... HIGH PRESSURE BUILDING INTO THEN SETTLING OVER CENTRAL NC WILL MAINTAIN VFR CONDITIONS THROUGH THURSDAY EVENING. SFC WINDS WILL VEER FROM A NORTH-NE DIRECTION EARLY THIS AFTERNOON TO AN EAST-SE DIRECTION BY EARLY EVENING. LATE THURSDAY MORNING INTO THE AFTERNOON...SCATTERED STRATOCUMULUS CLOUDS WILL DEVELOP WITH BASES 4000-6000FT. SFC WINDS WILL BE SLY AROUND 10KTS. THIS SLY FLOW WILL VEER TO A SW DIRECTION THURSDAY NIGHT AND ADVECT LOW LEVEL MOISTURE INTO THE REGION. THIS SHOULD LEAD TO THE DEVELOPMENT OF STRATUS...MAINLY OVER THE SOUTHERN AND WESTERN PIEDMONT WITH PATCHY FOG PROBABLE ELSEWHERE. THE STRATUS AND FOG WILL CAUSE A PERIOD OF MVFR/IFR CONDITIONS BY EARLY FRIDAY MORNING. IN ADDITION...IF SFC WINDS DECOUPLE...THERE COULD BE A PERIOD OF LOW LEVEL WIND SHEAR (DUE TO SPEED SHEAR) AS WINDS AT 1500FT SHOULD BE SW AROUND 40KTS. AREAS OF MVFR/IFR FRIDAY MORNING SHOULD GIVE WAY TO VFR CONDITIONS BY EARLY AFTERNOON. IT WILL BE BREEZY FRIDAY AFTERNOON AS A FRONTAL SYSTEM APPROACHES FROM THE WEST. WIND GUSTS ON THE ORDER OF 25-30KTS POSSIBLE. A PERIOD OF SUB VFR CONDITIONS APPEAR LIKELY FRIDAY NIGHT INTO EARLY SATURDAY AS THE FRONT CROSSES THE REGION...ACCOMPANIED BY SCATTERED- NUMEROUS SHOWERS. A RETURN TO VFR CONDITIONS EXPECTED SATURDAY AFTERNOON...PERSISTING INTO SUNDAY AND MONDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF NEAR TERM...WSS/RAH SHORT TERM...RAH LONG TERM...DJF AVIATION...WSS

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