Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230659 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 255 AM EDT WED JUL 23 2014 .SYNOPSIS...ATLANTIC HIGH PRESSURE WILL EXTEND WESTWARD OVER THE CAROLINAS TODAY. A COLD FRONT WILL APPROACH FROM THE NORTHWEST TONIGHT... THEN PUSH SOUTHEAST THROUGH NORTH CAROLINA THURSDAY AND THURSDAY NIGHT. WEAK HIGH PRESSURE WILL PUSH IN FROM THE NORTH ON FRIDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 255 AM WEDNESDAY... FOR TODAY/TONIGHT: ISOLATED SHOWERS ON THE PERIPHERY OF THE ATLANTIC RIDGE OFF THE SOUTHEAST COAST HAVE ALL BUT DIED OFF THIS MORNING. PATCHY FOG AND STRATUS WILL HOLD UNTIL SOON AFTER DAYBREAK (PRIMARILY OVER THE ERN HALF OF THE CWA)... FOLLOWED BY A TREND TO PARTLY TO MOSTLY SKIES AS A LIGHT SW SURFACE BREEZE INDUCES MIXING AND DISPERSION OF THE LOW LEVEL MOISTURE. DEEP LAYER SHEAR REMAINS LOW TODAY (10-15 KTS) WITH MARGINAL INSTABILITY (MLCAPE PEAKING AT 500-1000 J/KG) WITH MODEST MID LEVEL LAPSE RATES OF 5.5-6.0 C/KM. DYNAMICALLY WE SHOULD BE IN A RELATIVE LULL ZONE TODAY WITH THE MID LEVEL RIDGE CENTERED OFF THE SE COAST CONTINUING TO NOSE WESTWARD OVER THE SOUTHEAST... WHILE ENERGY DIVES FROM THE UPPER MIDWEST SOUTHEASTWARD TOWARD THE WRN OH VALLEY... HELPING DIG THE TROUGH JUST TO OUR NW TONIGHT AS THE ASSOCIATED SURFACE FRONT APPROACHES. PW VALUES REMAIN ELEVATED (1.7-2.1)... SO STILL EXPECT SCATTERED SHOWER/STORM ACTIVITY TODAY... BUT THE LACK OF DEEP SHEAR AND CONVECTIVE FOCUS AND THE WEAK MID LEVEL FLOW WILL HAMPER STORM ORGANIZATION AND STRENGTH. BOTH THE TRADITIONAL AND CONVECTION- ALLOWING MODELS BEAR THIS OUT WITH LIMITED COVERAGE TODAY... ALONG WITH A SHIFT IN BEST LOW LEVEL MOISTURE TRANSPORT TO COASTAL SECTIONS. WILL KEEP POPS AT 25-35% TODAY... PEAKING DURING THE TYPICAL MID-LATE AFTERNOON... AND TAPERING DOWN IN THE MID-LATE EVENING AS THE BOUNDARY LAYER STABILIZES AND PW DIPS SLIGHTLY. HIGHS 89-93 WITH NEAR-NORMAL THICKNESSES AND SOME SUNSHINE. LOWS 69-74 UNDER PARTLY TO MOSTLY CLOUDY SKIES. -GIH
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY/...
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AS OF 245 PM TUESDAY... BOTH THE GFS AND THE NAM SHOW A WEAKENING MID-LEVEL WAVE MOVING THROUGH CENTRAL NORTH CAROLINA THURSDAY AND THURSDAY NIGHT AS A TROUGH AXIS ALOFT PUSHES SLOWLY EAST. MEAN MOISTURE INCREASES THURSDAY WITH GOOD LIFT FORECAST BY THE GFS AND THE NAM. PRECIPITABLE WATER VALUES INCREASE TO AT OR JUST OVER TWO INCHES OVER MUCH OF CENTRAL NORTH CAROLINA THURSDAY...WITH THE HIGHEST VALUES ALONG AND EAST OF U.S. 1. DYNAMICALLY...THE GFS FORECASTS THE RIGHT ENTRANCE REGION OF A 60KT 300MB JET OVER CENTRAL NORTH CAROLINA BY 18Z THURSDAY...AND THIS JET GRADUALLY MOVES EAST INTO THURSDAY NIGHT. BUFR SOUNDINGS BECOME MOIST AND MORE UNSTABLE DURING THE DAY NORTHWEST TO SOUTHEAST...AND IT APPEARS AT LEAST GOOD CHANCE POPS FOR CENTRAL NORTH CAROLINA ARE WARRANTED...WHICH MAY BECOME LIKELY CHANCES OVER TIME OVER MUCH OF THE AREA. 1000-500MB LAPSE RATES ARE NOT REALLY HIGH BUT DECENT...TO 6.8C/KM...AND AS LOW-LEVEL WINDS AT BOTH 850MB AND 925MB ARE FORECAST TO ACTUALLY DIMINISH SOME DURING THE DAY FROM THE NORTHWEST...0-3KM SHEAR IS MODEST...MOSTLY IN THE TEENS KNOTS TO AROUND 20KT TOWARD THE VIRGINIA BORDER. THE BEST CAPE AROUND 18Z IS FORECAST BY THE GFS JUST WEST OF U.S. 1... AROUND 900J/KG...SHIFTING EAST DURING THE AFTERNOON WITH THE BETTER DOWNDRAFT CAPE CERTAINLY BETTER EAST OF U.S. 1. GIVEN A COMBINATION OF THESE MODEST PARAMETER VALUES...SCATTERED-TO-NUMEROUS SHOWERS AND THUNDERSTORMS WITH AN ISOLATED SEVERE WEATHER THREAT DUE TO WIND IS A REASONABLE FORECAST. IN A RELATIVE SENSE...THE BETTER CHANCE OF ISOLATED SEVERE WEATHER MAY BE ALONG AND EAST OF U.S. 1 DUE TO THE COMBINATION OF GREATER INSTABILITY AND LOW-LEVEL WIND. THERE APPEARS TO BE ENOUGH WIND AND SHEAR THAT STORMS SHOULD MOVE...POSING A LOCAL FLOOD THREAT TO THE TYPICAL URBAN AND POOR DRAINAGE LOCATIONS WHERE LOCAL TRAINING COULD OCCUR. 0-3KM HELICITY VALUES ARE LOW AND ACTUALLY GET LOWER...INTO THE LOWER DOUBLE DIGITS...DURING THE DAY. THE NAM IS A LITTLE FASTER WITH CLEARING AND INCREASING STABILITY OVERNIGHT THURSDAY COMPARED TO THE GFS...BUT NOT GREATLY SO...SUCH THAT CHANCES FOR PRECIPITATION BASED ON THE BUFR SOUNDINGS SHOULD WANE IN THE TRIAD BY 03Z...BY 06Z TOWARD KRDU...AND BY 09Z TOWARD INTERSTATE 95. DEPENDING ON THE DEGREE OF CLEARING...WITH THE WEAKENING FRONT MAKING SLOW PROGRESS SOUTH THERE COULD BE SOME AREAS OF FOG OVERNIGHT THURSDAY...BUT THE CONFIDENCE IN THIS DEPENDENT ON THE OVERALL DIMINISHING CLOUD COVER IS NOT HIGH ENOUGH TO PLACE IN THE FORECAST CURRENTLY. ON FRIDAY...ALTHOUGH THE WEAK SURFACE FRONT SHOULD START TO GET HUNG UP NEAR THE SOUTH CAROLINA BORDER AND TOWARD THE COAST...BUFR SOUNDINGS ESPECIALLY ON THE GFS BECOME FAIRLY STABLE TO DEEP CONVECTION. PRECIPITABLE WATER VALUES CONTINUE TO GRADUALLY DIMINISH...WITH VALUES APPROACHING AN INCH IN THE TRIAD BY 00Z SATURDAY. BOTH THE NAM AND THE GFS FORECAST MINIMAL QPF MAINLY ALONG AND EAST OF U.S. 1 FRIDAY AFTERNOON...AND GIVEN THE PROXIMITY OF THE SURFACE FRONT AND SLOWLY DIMINISHING MOISTURE... THERE MAY BE JUST ENOUGH INSTABILITY AND LIFT TO PROVIDE FOR ISOLATED SHOWERS OR THUNDERSTORMS FRIDAY AFTERNOON MAINLY OUTSIDE THE TRIAD...WHERE IT JUST SEEMS TOO STABLE FOR DEEP CONVECTION FRIDAY AFTERNOON. NAM BUFR SOUNDINGS HAVE QUITE HIGH MOISTURE AROUND 850MB WHILE THE GFS IS SOMEWHAT LESS...AND BLENDING THEM SHOULD RESULT IN SOME AREAS OF GOOD CU IN MUCH OF CENTRAL NORTH CAROLINA FOR A TIME FRIDAY ESPECIALLY AWAY FROM THE TRIAD. HIGHS THURSDAY MOSTLY A BLEND OF MOS...LEANING COOLER TOWARD THE TRIAD AND HIGHER TOWARD I-95 FOR VALUES FROM THE UPPER 80S TO MID 90S. LOWS THURSDAY NIGHT 67 TO 73...THEN HIGHS FRIDAY MOSTLY 85 TO 90...JUST A TOUCH COOLER THAN 1000-850MB THICKNESSES WOULD IMPLY DUE MOSTLY TO THE POTENTIAL FOR CU FOR A PERIOD THEN.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 240 AM WEDNESDAY... FRIDAY AND FRIDAY NIGHT: THE SURFACE FRONT AND THE UPPER LEVEL TROUGH WILL MOVE EAST OF MUCH OF CENTRAL NC BY FRIDAY...WITH WINDS VEERING TO THE NORTHWEST AND COOL HIGH PRESSURE BUILDING IN. IT APPEARS THAT THE COOLEST AIR MAY ONLY MAKE IT INTO THE FAR NW ON FRIDAY AS WEAK LOW PRESSURE IS EXPECTED TO SIT ALONG THE CAROLINA COAST FRIDAY AND FRIDAY NIGHT. HIGHS ON FRIDAY IN THE MID TO UPPER 80 WITH LOWS IN THE MID 60S TO AROUND 70 DEGREES EXPECTED. GIVEN THE LINGERING SFC LOW ALONG THE COAST AND THE FRONT STALLING IN THAT GENERAL VICINITY...THERE WILL BE THE CHANCE FOR ADDITIONAL SHOWERS AND STORMS ON FRIDAY...MAINLY ACROSS THE SOUTHEAST. PWATS WILL DECREASE TO UNDER AN INCH FOR FRIDAY AS MID LEVEL DRY AIR IS ADVECTED INTO THE REGION. SATURDAY THROUGH TUESDAY: THERE MAY BE A LINGERING CHANCE FOR SOME CONVECTION IN THE EAST SATURDAY WITH A SURFACE TROUGH AND WARM SOUTHERLY FLOW SETTING UP ALONG THE CAROLINA COAST. OTHERWISE... EXPECT MAINLY DRY WEATHER FOR MUCH OF THE AREA AS THE UPPER LEVEL TROUGH SHIFTS OFFSHORE. HIGHS WILL BE GENERALLY IN THE UPPER 80S TO LOW 90S AND LOWS IN THE UPPER 60S TO LOW 70S. THE PIEDMONT TROUGH WILL REMAIN IN PLACE SUNDAY AND SUNDAY NIGHT AS ANOTHER FRONTAL SYSTEM APPROACHES FROM THE WEST. EXPECT INCREASING CHANCES FOR CONVECTION...DIURNAL IN NATURE...SUNDAY AND MONDAY AS THE FRONT APPROACHES. ALTHOUGH THE TIMING OF THIS SYSTEM IS STILL A BIT UNCERTAIN...AS IS THE MODEL FORECAST PRECIPITATION...EXPECT THE BEST CHANCE OF CONVECTION ON MONDAY. AS OF THE LATEST (00Z) GFS MODEL RUN...THE FRONT SHOULD MOVE THROUGH THE AREA MONDAY NIGHT...WITH COOLER AND DRIER CONDITIONS FOR TUESDAY. SUNDAY SHOULD BE THE WARMEST DAY...HIGHS IN THE LOW TO MID 80S AND LOWS IN THE LOW TO MID 70S. TEMPERATURES ON MONDAY WILL DEPEND ON THE TIMING OF THE FRONT AND ITS ASSOCIATED CONVECTION...BUT FOR NOW WILL FORECAST HIGHS A FEW DEGREES COOLER THAN SUNDAY...MID 80S TO AROUND 90 DEGREES. NOTICEABLE TEMPERATURE CHANGE MONDAY NIGHT AND TUESDAY...WITH LOWS IN THE MID 60S TO AROUND 70 DEGREES AND HIGHS IN THE LOW TO MID 80S. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 1250 AM WEDNESDAY... PATCHY SHOWERS NEAR FAY ARE EXPECTED TO SLOWLY MEANDER ABOUT BEFORE WEAKENING AND DISSIPATING OVER THE NEXT FEW HOURS. THESE COULD AFFECT FAY WITH A PERIOD OF MVFR VSBY... BUT THE REMAINDER OF THE CENTRAL NC TAF AIRFIELDS SHOULD STAY DRY THIS MORNING. OTHERWISE... CONFIDENCE IS LOWER THAN IN PAST MORNINGS BUT IT APPEARS THAT ALL SITES ARE LIKELY TO SEE A PERIOD OF MVFR VSBYS PRIOR TO 12Z... AND SUB-MVFR CONDITIONS ARE LESS LIKELY GIVEN THE SPARCITY OF RAINFALL YESTERDAY. MVFR TO HIGH-END IFR CIGS ARE EXPECTED TO DOMINATE AT RWI THROUGH 13Z... WITH ONLY BRIEF MVFR OR HIGH-END IFR CIGS AT RDU/RWI... AND VFR CIGS LIKELY HOLDING AT INT/GSO. VFR CONDITIONS ARE LIKELY FROM 14Z ON THROUGH THE DAY AS CIGS LIFT AND BREAK UP WITH MIXING... WITH SURFACE WINDS FROM THE SW AT 8-12 KTS. ANY SHOWERS/STORMS WILL BE ISOLATED OR IN SMALL CLUSTERS... AND THE CHANCE OF THEM AFFECTING TAF SITES IS TOO SMALL TO INCLUDE IN THE TAFS AT THIS TIME. VFR CONDITIONS SHOULD PREVAIL THROUGH 06Z EXCEPT AT RWI... WHICH MAY SEE MVFR VSBYS IN FOG AFTER 03Z. LOOKING BEYOND 06Z EARLY THU MORNING... EXCEPT FOR SOME LIGHT FOG AT RWI... VFR CONDITIONS SHOULD HOLD ELSEWHERE OVERNIGHT WITH A LIGHT BREEZE FROM THE SW. AN APPROACHING COLD FRONT WILL BRING NUMEROUS SHOWERS AND STORMS WITH SUB-VFR CONDITIONS STARTING LATE MORNING (15Z-18Z) AT INT/GSO BEFORE SPREADING EAST TO RDU DURING THE EARLY AFTERNOON AND TO RWI/FAY DURING THE MID-LATE AFTERNOON. THE FRONT MAY SLOW DOWN OVER COASTAL SECTIONS THU NIGHT/FRI... KEEPING A CHANCE OF SUB-VFR SHOWERS/STORMS FRI AFTERNOON... BUT OTHERWISE VFR CONDITIONS ARE EXPECTED FRI-SAT AS HIGH PRESSURE NOSES IN FROM THE NORTH. AN UPPER LEVEL DISTURBANCE WILL MOVE IN FROM THE NORTHWEST ON SUNDAY... POTENTIALLY BRINGING ANOTHER ROUND OF SHOWERS/STORMS. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS..HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...DJF LONG TERM...KC AVIATION...HARTFIELD

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