Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230455 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1254 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/... AS OF 824 PM TUESDAY... ISOLATED SHOWERS HAVE GENERALLY DIED OFF IN THE PAST HOUR WITH THE EXCEPTION OF THE SANDHILLS AND SOUTHERN COASTAL PLAIN REGION WHERE SCATTERED SHOWERS AND THUNDERSTORMS CONTINUED AT MID EVENING. THE THUNDERSTORMS HAVE VERY SMALL CORES WITH SOME LOCALLY INTENSE RAINFALL. EVEN WITH THE SLOW MOVEMENT OF THESE STORMS... ONLY VERY LOCALIZED DOWNPOURS WERE OCCURRING WITH NO REPORTED RUNOFF PROBLEMS YET. THE AREAS AFFECTED EXTEND FROM NEAR SOUTHERN PINES TO FAYETTEVILLE AND FORT BRAGG EAST TO NEAR CLINTON. IT APPEARS THAT THESE STORMS ARE AGAIN LARGELY DIURNALLY DRIVEN. EXPECT THAT WITH INCREASING CINH IN THE NEXT FEW HOURS... THEY WILL DIE OFF QUICKLY AS WELL. OTHERWISE... THE ISOLATED SHOWERS WILL DIMINISH AS WELL. THIS SHOULD LEAVE MOSTLY CLEAR TO PARTLY CLOUDY SKIES OVERNIGHT. LOWS GENERALLY 68-73 N TO SE. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... AS OF 245 PM TUESDAY... ON WEDNESDAY...LOOKS LIKE MORE OF A CONVENTIONAL SUMMERTIME CONVECTIVE PATTERN WITH SOUTHWEST TO WESTERLY FLOW ALOFT ENHANCING LEE TROFFING OVER THE AREA. MIXING WILL BE DEEPER TO PROVIDE BREAKS IN THE CLOUDS TOMORROW AS WELL...ALLOWING HIGHS TO REACH THEIR POTENTIAL IN THE LOW 90S. WE WILL REMAIN IN THE SOUPY AIRMASS...OF COURSE...SO INSTABILITY WILL BE FAIRLY IMPRESSIVE...AROUND 1.5K JOULES...SO POPS IN THE 40 PERCENT RANGE ARE IN ORDER...GRADUATED SLIGHTLY HIGHER IN THE WEST WHERE DIFFERENTIAL HEATING SHOULD PROVIDE EARLIER INITIATION...AND EAST OF THE SURFACE TROF AXIS. SHEAR WILL BE MINIMAL...UNIDIRECTIONAL AROUND 15 KNOTS...SO ONLY A MARGINAL SEVERE THREAT. CONVECTION WILL WANE WITH LOSS OF INSOLATION AND WILL MAINTAIN A SLIGHT CHANCE OF A SHOWER OVERNIGHT. MINS WEDNESDAY NIGHT WILL BE MILD IN LIGHT SOUTHWEST FLOW...72-75. 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. && .LONG TERM /THURSDAY THROUGH TUESDAY/... AS OF 300 PM TUESDAY... FOR THE PERIOD FRIDAY NIGHT THROUGH TUESDAY...THE GFS AND THE ECMWF ARE FAIRLY CONSISTENT IN MOVING THE UPPER-LEVEL TROUGH AXIS JUST EAST OF CENTRAL NORTH CAROLINA OVERNIGHT FRIDAY INTO SATURDAY. BOTH SETS OF GUIDANCE ALLUDE TO WEAK SHORTWAVE RIDGING SATURDAY NIGHT... FOLLOWED BY A MID-LEVEL SHORTWAVE MOVING THROUGH SOMETIME ON SUNDAY WITH THE TYPICAL TIMING DIFFERENCES OUT TO THE FIFTH DAY. AS AN UPPER-LEVEL TROUGH DEEPENS OVER THE EASTERN UNITED STATES EARLY NEXT WEEK...BACKING WINDS ALOFT MORE TO THE SOUTHWEST OCCUR. THE GFS AND ECMWF ARE BOTH DRY FRIDAY NIGHT AND MOSTLY DRY SATURDAY BEHIND THE TROUGH ALOFT AND UNDER WEAK HIGH PRESSURE ESPECIALLY EARLY SATURDAY FOLLOWED BY WEAK SURFACE TROUGH DEVELOPMENT SATURDAY AFTERNOON. FOR NOW...RETAINED THE SLIGHT CHANCE OF THUNDERSTORMS ALONG AND EAST OF THE INTERSTATE 95 CORRIDOR FOR SATURDAY WITH THE ECMWF SHOWING THE PRESENCE OF SOME MID-LEVEL MOISTURE...BUT GFS MODEL SOUNDINGS ARE STABLE AND IF THE CURRENT TREND OF CHANCES BELOW CLIMATOLOGY CONTINUES EVEN THESE SMALL CHANCES MAY EVENTUALLY BE REMOVED FROM THE FORECAST. 1000-850MB THICKNESSES ARE WARMEST SUNDAY AND THAT MAY BE THE WARMEST DAY OF THE LONG-TERM PERIOD BEFORE LOWERING HEIGHTS ALOFT TAKE PLACE. THE ECMWF IS MUCH MORE MOIST AND UNSTABLE SUNDAY COMPARED TO THE GFS AND WILL MAINTAIN THE CHANCES FOR SHOWERS AND STORMS WITH THE HIGHER CHANCES ALONG AND NORTH OF U.S. 64 CLOSER TO THE EXPECTED TRACK OF ANY MID-LEVEL SHORTWAVE AND AN APPROACHING SURFACE FRONT. WITH THE DEEPENING TROUGH...BOTH THE GFS AND ECMWF CURRENTLY MOVE THE SURFACE FRONT THROUGH CENTRAL NORTH CAROLINA MONDAY INTO EARLY TUESDAY...LINGERING A SURFACE TROUGH NEAR THE CAROLINA COAST. WHILE CHANCES FOR PRECIPITATION INCREASE CLOSER TO CLIMATOLOGY EARLY NEXT WEEK ESPECIALLY ON THE GFS...GENERAL QPF IS NOT TERRIBLY HIGH AND THEN HIGHER RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA ALONG AND EAST OF U.S. 1. THIS COULD BE...IN PART...DUE TO MORE OF A WESTERLY LOW-LEVEL FLOW ON FORECAST MODEL SOUNDINGS OVER THE WESTERN PIEDMONT...AT LEAST FOR MONDAY. STILL...WILL FORECAST A CHANCE OF SHOWERS AND THUNDERSTORMS THROUGHOUT CENTRAL NORTH CAROLINA MONDAY WITH THE FRONT AND THEN A SLIGHT CHANCE IN THE TRIAD AND CHANCES ELSEWHERE ON THE SEVENTH DAY...HIGHER THEN TOWARD KFAY AND KGSB...BASED ON THE EXPECTED SURFACE FRONTAL POSITION AND THE SOUTHWEST FLOW ALOFT. && .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...32 SHORT TERM...DJF LONG TERM...DJF AVIATION...HARTFIELD

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