Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 221910 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 310 PM EDT TUE JUL 22 2014 .SYNOPSIS...A SURFACE FRONT ALONG THE COAST WEAKENS OVERNIGHT AND EARLY WEDNESDAY AHEAD OF A COLD FRONT. THIS COLD FRONT WILL MOVE THROUGH MUCH OF THE REGION THURSDAY AND THURSDAY NIGHT...SLOWING AND WEAKENING AS IT APPROACHES SOUTH CAROLINA EARLY FRIDAY. THE WEAK FRONT THEN LINGERS NEAR THE SOUTH CAROLINA BORDER AND THE NORTH CAROLINA COAST THROUGH FRIDAY NIGHT. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
AS OF 310 PM TUESDAY... SHOWER CONVERAGE WAS LIMITED BY THE LACK OF FORCING AND MINIMAL UPPER SUPPORT THIS AFTERNOON. WHILE ONGOING WIDELY SCATTERED CONVECTION WILL DIMINISH AS THE EVENING SETS IN...THERE WILL BE POTENTIAL FOR SHOWERS TO MIGRATE WEST INTO THE COASTAL AREAS THROUGH MIDNIGHT AS THE RETROGRESSING COASTAL TROF WILL PROVIDE A BIT OF EXTRA IMPETUS WITH MODEST LOW LEVEL CONVERGENCE. MINS WILL BE PERSISTENCE FROM LAST NIGHT... 70-72. 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.
-- End Changed Discussion --
&& .SHORT TERM /THURSDAY THROUGH FRIDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --
&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --
&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 130 PM TUESDAY... FOR THE CURRENT TAF PERIOD...SPOTTY SHOWERS AND ISOLATED THUNDERSTORMS THIS AFTERNOON WILL LINGER INTO THE EVENING...WANING WITH LOSS OF HEATING. CONDITIONS WILL BE VFR EXCEPT FOR MVFR TO BRIEFLY IFR IN THE VICINITY OF CONVECTION. A TYPICAL BRIEF PERIOD OF MVFR TO BRIEFLY IFR CIGS AND VSBY IS EXPECTED TONIGHT IN THE 08-13Z TIME FRAME...EXCEPT THAT CONDITIONS WILL BE LOWER AND DEVELOP A COUPLE OF HOURS SOONER AT SITES THAT RECEIVE RAIN THIS AFTERNOON/EVENING. WINDS WILL BE MORE UNIFORMLY OUT OF THE SOUTHWEST TOMORROW...BUT STILL LIGHT...LESS THAN 10 KNOTS. AGAIN EXPECT WIDELY SCATTERED CONVECTION... MAINLY AFTER 18Z...WITH BETTER POTENTIAL FOR SHOWERS IN THE WEST... GSO/INT...AND AT FAY WHERE CONDITIONS WILL BE A LITTLE MORE UNSTABLE. SOUTHWEST FLOW WILL CONTINUE THROUGH THURSDAY AS A FRONT APPROACHES FROM THE WEST. SHOWERS AND THUNDERSTORMS WILL BE MORE WIDESPREAD ON THURSDAY INTO EARLY THURSDAY NIGHT. THERE WILL BE A LINGERING CHANCE OF CONVECTION IN THE EAST... RWI/FAY...INTO THE WEEKEND AS THE FRONT STALLS ALONG THE COAST...OTHERWISE VFR CONDITIONS ARE EXPECTED FRIDAY THROUGH SUNDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF NEAR TERM...MLM SHORT TERM...DJF LONG TERM...DJF AVIATION...MLM

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.