Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 271446 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1046 AM EDT WED AUG 27 2014 .SYNOPSIS...HIGH PRESSURE WILL EXTEND SOUTHWARD INTO THE REGION TODAY. A BACK DOOR COLD FRONT WILL SETTLE SOUTH INTO CENTRAL NC THU AND THU NIGHT. && .NEAR TERM /THROUGH THURSDAY/...
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AS OF 1045 AM WEDNESDAY... THE EARLY MORNING STRATUS THAT DEVELOPED ACROSS THE EAST HAS BURNED OFF QUICKLY OVER THE LAST COUPLE OF HOURS AND HAS LEFT MOSTLY SUNNY SKIES IN ITS WAKE. OTHERWISE...HURRICANE CRISTOBAL WILL CONTINUE TO ACCELERATE OFF TO THE NORTHEAST (BUT WELL OFFSHORE)...LEAVING CENTRAL NC ON THE DRY SUBSIDENT SIDE OF THE STORM. THIS ALONG WITH THE FACT THAT PWAT VALUES WILL REMAIN BELOW 1 INCH...ANOTHER DRY AND PLEASANT DAY IS EXPECTED. WITH MAX LOW LEVEL THICKNESS VALUES PROGGED TO BE 15-20M HIGHER TODAY...HIGH TEMPS SHOULD BE 3-5 DEGREES WARMER TODAY THAN YESTERDAY. THEREFORE...GENERALLY MID TO UPPER 80S ARE EXPECTED. -KRD SURFACE HIGH PRESSURE AND THE CORE OF THE LOWER PW`S ARE FORECAST TO DRIFT TO THE SOUTH OF THE AREA OVERNIGHT AS A BACKDOOR COLD FRONT BEGINS TO APPROACH THE AREA FROM THE NORTH... ASSOCIATED WITH THE S/W TROUGH THAT IS FORECAST TO ABSORB HURRICANE CRISTOBAL AND SWEEP HIM QUICKLY OFF TO THE NORTHEAST (AWAY FROM ANY COASTAL AREAS IN THE U.S.). LOWS TONIGHT WILL AGAIN BE COMFORTABLE FOR LATE AUGUST IN CENTRAL NC... BELOW NORMAL IN THE LOWER TO MID 60S... MAYBE EVEN A FEW LOCATIONS TOUCHING THE UPPER 50S. THURSDAY: THE PREVIOUSLY MENTIONED BACKDOOR COLD FRONT IS EXPECTED TO DROP SOUTHWARD INTO CENTRAL NC THURSDAY AFTERNOON. MOISTURE WILL INCREASE ACROSS THE AREA IN ADVANCE OF THIS FEATURE. HOWEVER... WITH LOW LEVEL WESTERLY TO WEST-SOUTHWESTERLY FLOW IN ADVANCE OF THE SYSTEM WE SHOULD SEE DEWPOINTS IN THE LOWER TO MAYBE MID 60S (AS THE FRONT APPROACHES... POOLING ALONG IT). THIS SHOULD LEAD TO ONLY ISOLATED CONVECTION DEVELOPING IN THE AFTERNOON ACROSS NORTHERN PORTIONS OF THE AREA. HOWEVER... WE SHOULD WARM UP NICELY ON THURSDAY... WITH THE WSW TO W`ERLY FLOW. THUS... EXPECT HIGH TEMPS TO BE IN THE LOWER TO MID 90S. WRT A SEVERE THREAT... SEVERE WEATHER POTENTIAL LOOKS TO BE LOW... GIVEN THE RATHER WEAK INSTABILITY... THANKS TO THE RELATIVELY DRY LOW LEVELS. THE NAM APPEARS TO BE TOO MOIST AND CONSEQUENTLY GENERATES TOO MUCH INSTABILITY AS NOTED IN THE PREVIOUS AFD FOR THE PATTERN. IN ADDITION... DEEP LAYER SHEAR IS FORECAST TO REMAIN WEAK... ~20KTS OR SO. THUS... WE ARE NOT OUTLOOKED IN THE SPC DAY 2 CONVECTIVE OUTLOOK IN ANYWAY. IF WE GET A DECENT STORM DEVELOP THOUGH IT WOULD HAVE A DAMAGING WIND THREAT THANKS TO THE DRY DEEP SUB-CLOUD LAYER.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... AS OF 3 AM WEDNESDAY... BACKDOOR FRONT PROJECTED TO STALL IN VICINITY OF THE NORTHERN PIEDMONT-NORTHERN COASTAL PLAIN THURSDAY NIGHT THEN SLOWLY DISSOLVE ON FRIDAY. ENOUGH MOISTURE POOLING ALONG THIS FEATURE MAY AID TO TRIGGER AN ISOLATED SHOWER OVERNIGHT THURSDAY NIGHT TO THE NORTH-EAST OF RDU...WITH AN ISOLATED SHOWER OR T-STORM POSSIBLE OVER THE SAME REGION FRIDAY AFTERNOON. BUILDING MID-UPPER LEVEL HEIGHTS AND ASSOCIATED MID LEVEL SUBSIDENCE WILL INHIBIT CONVECTIVE DEVELOPMENT ELSEWHERE. AFTERNOON THICKNESSES STILL AVERAGING 10M ABOVE NORMAL...SUPPORTIVE OF MAX TEMPS ABOUT 3-4 DEGREES ABOVE NORMAL. THIS YIELDS HIGH TEMPS FRIDAY IN THE 90-95 DEGREE RANGE. MIN TEMPS WILL BE IN THE MID-UPPER 60S THURSDAY NIGHT AND UPPER 60S-AROUND 70 FRIDAY NIGHT. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 3 AM WEDNESDAY... SATURDAY...PRESENCE OF MID-UPPER LEVEL RIDGE OVER THE FORECAST AREA SHOULD INHIBIT CONVECTIVE DEVELOPMENT DUE TO SUBSIDENCE INVERSION ALOFT. STILL EXPECT AN EXTENSIVE CUMULUS FIELD AS LOW LEVEL MOISTURE WILL BE IN THE INCREASE...WITH SOME GROWTH TO THE CU UNTIL IT HITS THE INVERSION. MODEL GUIDANCE PLACES THE 700MB ANTI-CYCLONE DIRECTLY OVERHEAD. THIS FAVORABLE PLACEMENT SUGGEST MAX TEMPS BACK IN THE 90- 95 DEGREE RANGE. SATURDAY NIGHT SHOULD SEE PARTLY CLOUDY SKIES WITH PATCHES OF FOG DEVELOPING LATE. MIN TEMPS IN THE UPPER 60S-LOWER 70S. MID/UPPER LEVEL RIDGE WILL GRADUALLY DRIFT EAST AND WEAKEN WITH TIME. INCREASING SW FLOW ALOFT WILL INCREASE MOISTURE IN THE UPPER LEVELS OF THE ATMOSPHERE. WHILE MODEL GUIDANCE SUGGEST THAT THE BULK OF BEST UPPER LEVEL SUPPORT FOR CONVECTION WILL REMAIN WEST-NW OF OUR REGION...WEAK PERTURBATIONS IN THE FLOW ALOFT INTERACTING WITH AVAILABLE MOISTURE AND WEAK-MODERATE LOW LEVEL INSTABILITY WILL SUPPORT THE DEVELOPMENT OF ISOLATED TO SCATTERED CONVECTION SUNDAY AFTERNOON-EVENING...AND SCATTERED CONVECTION MONDAY AFTERNOON- EVENING. MAY SEE CONVECTION BECOME A LITTLE MORE CONCENTRATED/ORGANIZED MONDAY AND MORE SO TUESDAY AS MID LEVEL TROUGH APPROACHES AND CROSSES THE REGION. (GFS AS MUCH AS 12=18 HOURS FASTER COMPARED TO THE ECMWF. PER INITIALIZATION TONIGHT OFF TEH PACIFIC NW...SLOWER ECMWF PREFERRED AT THIS TIME.) RAINFALL ASSOCIATED WITH THE HEAVIER SHOWERS AND STORMS MAY BE LOCALLY HEAVY AS AIR MASS WILL BECOME TROPICAL-LIKE. PRECIPITABLE WATER VALUES PREDICTED TO RETURN TO NEAR 2 INCHES BY LATE SUNDAY OR MONDAY. OUR STRETCH OF ABOVE NORMAL TEMPS EXPECTED TO PERSIST ITO EARLY NEXT WEEK WITH MAX TEMPS IN THE UPPER 80S NW-LOWER 90S SE. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/... AS OF 635 AM WEDNESDAY... 24 HOUR TAF PERIOD: CANADIAN HIGH PRESSURE OVERHEAD...BETWEEN A COLD FRONT APPROACHING FROM THE MIDWEST AND HURRICANE CRISTOBAL OFFSHORE...WILL RESULT IN MAINLY VFR CONDITIONS THROUGH THE TAF PERIOD. HOWEVER... AN AREA OF LOW STRATUS AND FOG HAS DEVELOPED/MOVED INTO EASTERN PORTIONS OF THE AREA THIS MORNING... CREATING LIFR CONDITIONS AT KRWI. THIS AREA OF LOW CLOUDS AND FOG IS EXPANDING WEST AND SOUTHWARD THIS MORNING. HOWEVER... CONFIDENCE THAT IT WILL REACH KFAY AND/OR KRDU BEFORE IT BEGINS TO LIFT IS LOW TO MODERATE. THINK WE WILL STILL SEE A BRIEF PERIOD OF STRATOCUMULUS THIS MORNING FROM THE MOISTURE IN THE LOW LEVEL NE TO NNE LOW LEVEL FLOW COMBINED WITH DAYTIME HEATING AT KRDU AND KFAY THOUGH. EXPECT THIS CLOUD COVER WILL LIFT AND SCATTER BY MID TO LATE MORNING... WITH VFR EXPECTED BY AFTERNOON EVERYWHERE AT THE LATEST. OTHERWISE... A GENERALLY LIGHT NORTHERLY SFC WIND IS EXPECTED TODAY (5-10 KTS). HOWEVER... THERE WILL LIKELY BE A SHORT PERIOD OF SOMEWHAT STRONGER WINDS (8-12 KTS WITH GUSTS INTO THE MID-UPPER TEENS KTS... MAINLY AT KFAY/KRWI) AT EASTERN SITES MID-MORNING TO MIDDAY TODAY...WHERE THE MSLP PRESSURE GRADIENT WILL BE RESIDUALLY TIGHT EARLY IN THE DAY...BETWEEN THE OVERHEAD SFC HIGH AND THE OFFSHORE HURRICANE. THE LOW LEVEL FLOW IS EXPECTED TO BECOME MORE NORTHWEST TO WESTERLY OVERNIGHT. THUS... DO NOT EXPECT A REPEAT PERFORMANCE OF IFR/LIFR MORNING FOG AND/OR LOW STRATUS ON THURSDAY MORNING. HOWEVER... CAN NOT COMPLETELY RULE OUT SOME MVFR VISBYS AT KRWI IN THE PRE-DAWN HOURS OF THURSDAY... THOUGH PROBABILITIES ARE WAY TOO LOW TO INCLUDE IN THE TAF AT THIS TIME. OUTLOOK: THE ARRIVAL OF THE COLD FRONT APPROACHING FROM THE UPPER MIDWEST WILL RESULT IN A SMALL CHANCE OF AN AFTERNOON SHOWER OR STORM THU AND FRI...AS WELL AS A CHANCE OF MVFR CEILINGS IN BRIEF NE FLOW THU NIGHT FROM KRWI AND ESPECIALLY POINTS NORTHEASTWARD... INTO NE NC AND TIDEWATER VA. THE PROBABILITY OF PATCHY FOG WILL ALSO INCREASE BY THE WEEKEND...AS THE LOW LEVEL FLOW ASSUMES A MORE SOUTHERLY (MOIST) COMPONENT. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BSD/MWS NEAR TERM...KRD/BSD SHORT TERM...WSS LONG TERM...WSS AVIATION...BSD/MWS

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