Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301041 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 640 AM EDT TUE SEP 30 2014 .SYNOPSIS...WEAK LOW PRESSURE OVER NORTHEAST FLORIDA WILL TRACK NORTHEASTWARD OFF THE SOUTHEAST COAST TODAY. WEAK HIGH PRESSURE WILL BUILD OVER THE AREA FROM THE NORTH WEDNESDAY THROUGH THURSDAY. A STRONG STORM SYSTEM WILL APPROACH FROM THE WEST ON FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 330 AM TUESDAY... UPDATE: FOG HAS BECOME QUITE DENSE OVER MOST OF CENTRAL NC (WITH THE EXCEPTION OF THE FAR SOUTHEAST SECTIONS)... WARRANTING ISSUANCE OF A DENSE FOG ADVISORY UNTIL 10 AM. VSBYS SHOULD GRADUALLY IMPROVE DURING THE 9AM-11AM TIME FRAME. EARLIER DISCUSSION FROM 222 AM TUESDAY... TODAY... FIRST CONCERN EARLY THIS MORNING IS THE DEGREE OF FOG DEVELOPMENT OVER THE AREA THUS FAR. THE MID LEVEL SHORTWAVE TROUGH IS NOW HEADING EAST OFF THE CAROLINA COAST... WITH THE VEIL OF MID/HIGH CLOUDS DEPARTING ALONG WITH IT. THE DAMP GROUND COMBINED WITH THE CLEARING SKIES AND LIGHT/CALM WINDS SHOULD CONTINUE TO FOSTER DEVELOPMENT OF LOW CLOUDS AND FOG EARLY THIS MORNING... ALTHOUGH THE CURRENT PATCHY/FLEETING NATURE OF THESE CONDITIONS (SEVERAL SITES HAVE BOUNCED AROUND BETWEEN 1/4 MI AND 5 MI IN FOG THE LAST FEW HRS) GIVES US PAUSE AS TO THE NEED FOR A DENSE FOG ADVISORY. THE HRRR DEPICTS A FAIRLY SOLID DECK OF LOW CLOUDS/FOG FORMING OVER THE NEXT FEW HOURS HOWEVER. WILL CONTINUE TO MONITOR THE OBSERVED TRENDS. IF VSBYS DO DROP AND HOLD THERE FOR OVER AN HOUR... THEY`RE LIKELY TO HOLD FIRM THROUGH MID MORNING... GIVEN THE WEAK WIND FIELD THROUGH THE LOWEST FEW THOUSAND FEET RESULTING IN MINIMAL STIRRING/DISPERSION HORIZONTALLY OR VERTICALLY. WILL KEEP SKIES PARTLY TO MOSTLY CLOUDY THROUGH MID MORNING TO ACCOUNT FOR THIS. THEN... ONCE HEATING AND SUBSEQUENT MIXING HELPS TO DISPERSE THE FOG/STRATUS... EXPECT A GOOD BIT OF SUNSHINE THROUGH THE DAY... WITH FLAT AFTERNOON STRATOCU LIKELY TO STAY SCATTERED AT WORST. WITH THICKNESSES CLOSE TO SEASONAL NORMALS... STILL LOOK FOR HIGHS WITHIN A FEW DEGREES OF 80. FOR TONIGHT: THE SURFACE LOW TRACKING TOWARD THE NE WELL OFF THE SE COAST WILL BE FAR ENOUGH TO OUR SE TO MINIMIZE ANY IMPACT ON CENTRAL NC. THE WEAK LOW LEVEL FLOW PATTERN HOLDS WITH A WEAK HIGH PRESSURE RIDGE SPANNING THE AREA AND A VERY WEAK SURFACE LOW/INVERTED TROUGH OVER PA/WV/VA... A REFLECTION OF THE CLIPPER MID LEVEL VORTEX NOW OVER ERN MI THAT IS EXPECTED TO CROSS THE MIDATLANTIC REGION REGION LATE TONIGHT THROUGH WED MORNING. MODELS VARY IN THEIR IMPACTS ON OUR WEATHER WITH THIS FEATURE... WITH THE NAM MUCH MORE BULLISH THAN THE GFS IN TAKING A SLUG OF 850-700 MB MOISTURE EAST ACROSS THE AREA TONIGHT. THIS SEEMS A BIT OVERDONE BUT IT IS SOMEWHAT SUPPORTED BY OBSERVED SOUNDINGS UPSTREAM... SO WILL RETAIN A FEW CLOUDS OVER THE AREA OVERNIGHT... AND LATER FORECASTS CAN INCREASE THIS COVERAGE IF LATER GUIDANCE SUPPORTS THE NAM. LOWS 57-60. -GIH && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... AS OF 245 AM TUESDAY... AS NOTED ABOVE... WE SHOULD SEE AT LEAST SOME SCATTERED CLOUDS MAINLY OVER THE EAST WED MORNING. THE PRESENCE OR LACK OF SUCH CLOUDS WILL IMPACT HOW MUCH FOG FORMS WED MORNING. WE SHOULD SEE AT LEAST SOME LIGHT FOG TO START THE DAY... AND PERHAPS MORE DENSE IF THE AFOREMENTIONED CLIPPER-ASSOCIATED CLOUDS DO NOT HAPPEN. OTHERWISE... EXPECT A PARTLY TO MOSTLY SUNNY DAY. THE CLIPPER LOW WILL CROSS NEW ENGLAND AS THE STRONG VORTICITY MAX ROUNDS ITS BASE... SHIFTING OFF THE NJ COAST... AND WE SHOULD SEE A BIT MORE FLAT DAYTIME CUMULUS FROM THE TRIANGLE NORTH AND EAST CLOSER TO THE LOW. MODELS SHOW WEAK MID LEVEL RIDGING PUSHING IN FROM THE WEST LATE... BETWEEN THE DEPARTING CLIPPER AND A DEEPENING TROUGH COVERING THE EASTERN ROCKIES AND HIGH PLAINS LATE WED/WED NIGHT. WHILE MODELS SHOW A MINOR PERTURBATION TRACKING EASTWARD OVER THE SOUTHEAST STATES WED NIGHT... THIS SHOULD BE OF LITTLE CONSEQUENCE WITH DEEP DRY AIR MOVING IN. EXPECT DRY WEATHER THROUGH WED NIGHT. THICKNESSES ARE EXPECTED TO START WED ABOUT 10 M ABOVE NORMAL... SUPPORTING HIGHS ABOUT A CATEGORY ABOVE NORMAL... 80-84. SOME CLOUDINESS POSSIBLE WED NIGHT ESPECIALLY OVER THE WEST WHERE MODELS INDICATE AN UPTICK IN LOW LEVEL MOISTURE TRANSPORT GENERATED BY LIGHT BUT CONFLUENT AND UPSLOPE-DIRECTED LOW LEVEL FLOW. LOWS WITHIN A COUPLE DEGREES OF 60. -GIH && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 300 AM TUESDAY... FOR THE PERIOD THURSDAY THROUGH THURSDAY NIGHT...A MID-LEVEL RIDGE AXIS BUILDS INTO CENTRAL NORTH CAROLINA THURSDAY...WITH THE AXIS MOVING EAST THURSDAY NIGHT. THE GUIDANCE HAS CONTINUED TO FORECAST VERY MINOR QPF IN CENTRAL NORTH CAROLINA DURING THIS PERIOD...WITH THE GFS FORECASTING THIS THURSDAY AND THE NAM MORE THURSDAY NIGHT. THE GFS DOES HAVE A RELATIVE MAXIMUM OF 850MB THETA-E AIR OVER CENTRAL NORTH CAROLINA THURSDAY WITH WEAK 850MB LIFT...BUT HEIGHTS ALOFT ARE RISING AND ANY LOW-LEVEL FORCING WITH ANY SURFACE BOUNDARY SHOULD BE WEAK. LIFTED INDICES ARE ABOVE 0C...AND MLCAPE IN THE LOWEST KM DOES NOT REGISTER AS BUFR SOUNDINGS FROM BOTH THE NAM AND GFS APPEAR CAPPED. GIVEN THE ORIENTATION OF 1000-500MB THICKNESSES...POSSIBLY A SHOWER COULD DRIFT SOUTHEAST FOLLOWING THE THERMAL WIND FROM HIGHER TERRAIN AND GET CLOSE TO THE NORTHWEST PIEDMONT THURSDAY AFTERNOON OR EVENING...BUT GIVEN THE UNCERTAINTY WILL KEEP THE FORECAST DRY. MOS GUIDANCE POPS ARE IN SINGLE FIGURES IN BOTH THE MAV AND THE MET. WITH AT LEAST A PARTLY SUNNY SKY EXPECTED...1000-850MB THICKNESSES WOULD SUGGEST LOWER TO MID 80S FOR HIGHS...IN CONJUNCTION WITH MAV AND MET MOS GUIDANCE. OVERNIGHT LOWS THURSDAY NIGHT NEAR 60 IN THE NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN UNDERNEATH THE RIDGE AXIS ALOFT FOR A GOOD PART OF THE NIGHT...LOWER 60S ELSEWHERE AND POSSIBLY ON THE HIGHER END OF THE LOWER 60S TOWARD THE TRIAD AS THE WINDS OFF OF THE SURFACE START TO INCREASE OVERNIGHT. FOR THE PERIOD FRIDAY THROUGH TUESDAY...THE ECMWF AND THE GFS CONTINUE TO BE IN FAIRLY GOOD AGREEMENT WITH THE TIMING OF AN ELONGATED MID-LEVEL SHORTWAVE MOVING INTO CENTRAL NORTH CAROLINA BY 00Z SATURDAY AND THEN EAST OF THE AREA BY 12Z SATURDAY. ONE TREND HAS BEEN FOR THE MID-LEVEL RIDGE TO BE SLIGHTLY MORE AMPLIFIED... WHICH...IF THE TREND CONTINUES...COULD SLOW THE ONSET OF ANY SHOWERS OR THUNDERSTORMS DURING THE DAY FRIDAY. LAPSE RATES ON COARSE GFS AND ECMWF MODEL SOUNDINGS ARE NEAR MOIST ADIABATIC AT BEST...SO INSTABILITY SHOULD BE LIMITED. STILL...WITH WINDS OFF OF THE SURFACE INCREASING TO AT OR A LITTLE ABOVE 30KT AHEAD OF THE COLD FRONT... CURRENT THINKING IS THAT ANY STRONGER STORM COULD HAVE A GUSTY WIND...THOUGH NOT CONFIDENT CURENTLY IN THE PROBABILITY OF ISOLATED SEVERE WEATHER GIVEN THE MARGINAL LAPSE RATES. DRY CONDITIONS WILL BE FORECAST SATURDAY THROUGH SUNDAY...THOUGH THE ECMWF DOES CONTINUE TO FORECAST GREATER DIGGING WITH UPPER-LEVEL LOW PRESSURE MOVING THROUGH THE OHIO VALLEY AND EAST ACROSS AREAS JUST NORTH OF CENTRAL NORTH CAROLINA SATURDAY NIGHT. AGAIN...THE TREND OF THIS WILL NEED TO BE WATCHED...BUT CURRENTLY THE MID-LEVEL MOISTURE ASSOCIATED WITH THE UPPER LOW ON THE ECMWF STAYS NORTH OF CENTRAL NORTH CAROLINA SATURDAY NIGHT INTO EARLY SUNDAY. BEHIND THE COLD FRONT ON SATURDAY OR SATURDAY NIGHT...HOWEVER...SOME JET STREAK CIRRUS COULD OCCUR IF THE GFS AND ECMWF UPPER-LEVEL MOISTURE FORECASTS VERIFY IN CONJUNCTION WITH THE JET AXIS ALOFT. THE ECMWF IS ALSO MORE AMPLIFIED WITH ANOTHER IN A SERIES OF MID- LEVEL WAVES IN THE NORTHWEST FLOW...THIS ONE APPROACHING THE SOUTHERN APPALACHIANS MONDAY. THE GFS IS DRY WITH LITTLE FORCING... WHILE THE ECMWF HAS MORE OF A SURFACE REFLECTION WITH THE MID-LEVEL WAVE AND ENOUGH MID-LEVEL MOISTURE FOR LIGHT PRECIPITATION OVER THE WESTERN AND NORTHWEST PIEDMONT LATE MONDAY AFTERNOON OR MONDAY NIGHT. WITH SURFACE HIGH PRESSURE OVER THE GULF...IF THERE IS ANY PRECIPITATION MONDAY...THE THOUGHT IS IT WOULD BE MID-LEVEL DRIVEN AND MOSTLY LIGHT. FOR THIS FORECAST WILL TREND A LITTLE MORE PESSIMISTIC ON THE LAST DAY OF THE LONG-TERM PERIOD...INCREASING CLOUDS BUT KEEPING THE OVERALL FORECAST DRY. AFTER HIGHS IN THE MID 70S TO NEAR 80 FRIDAY AHEAD OF THE FRONT... BY SATURDAY NIGHT...AS THE GUIDANCE STILL SHOWS CHILLY 1000-850MB THICKNESSES INTO THE 1340S...THERE SHOULD BE AT LEAST A FEW 40S OVER THE WESTERN AND NORTHERN PIEDMONT. MODEST WARMING FOR THE END OF THE WEEKEND AND THE START OF NEXT WEEK. HIGHS SHOULD BE BACK AT LEAST IN THE LOWER TO MID 70S FOR MONDAY. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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AS OF 640 AM TUESDAY... ADVERSE AVIATION CONDITIONS ARE LIKELY TO HOLD OVER CENTRAL NC THROUGH 14Z OR 15Z THIS MORNING... WITH IMPROVEMENT TO VFR TO FOLLOW BY LATE MORNING... WHICH WILL HOLD THROUGH 04Z (MIDNIGHT TONIGHT). THE MID LEVEL TROUGH AXIS OVER THE ERN CAROLINAS WILL CONTINUE TO SHIFT EAST AND OFFSHORE THIS MORNING. THE RESULTANT CLEARING SKIES AND LIGHT WINDS HAVE LED TO LOW STRATUS/FOG DEVELOPMENT THIS MORNING. THESE IFR/LIFR CONDITIONS HAVE BEEN DISCONTINUOUS... WITH AVIATION CONDITIONS PERIODICALLY SWINGING WILDLY BETWEEN LIFR AND MVFR... MAKING THE TAFS CHALLENGING THIS MORNING. PILOTS SHOULD BE PARTICULARLY ALERT FOR POSSIBLE VFR HOLES WITHIN IFR/LIFR CONDITIONS THROUGH MID MORNING. OTHERWISE... ANY CIGS SHOULD LIFT AND BEGIN TO BREAK UP BY 15Z OR 16Z... WITH VFR CONDITIONS THEN PREVAILING THROUGH THE AFTERNOON AND EVENING HOURS. AFTER MIDNIGHT... WE EXPECT REDEVELOPMENT OF SHALLOW IFR OR LIFR FOG LATE IN THE TAF VALID PERIOD... WITH THE WORST CONDITIONS EXPECTED BETWEEN 08Z AND 12Z. SURFACE WINDS WILL REMAIN LIGHT/VARIABLE (MAINLY FROM THE NORTHWEST) MOSTLY UNDER 5 KTS TODAY/TONIGHT. LOOKING BEYOND 12Z WED MORNING... SUB-VFR FOG EARLY WED MORNING SHOULD MIX OUT BY 15Z. OTHERWISE... VFR CONDITIONS WILL PREVAIL THROUGH FRI... ALTHOUGH SHALLOW IFR GROUND FOG IS AGAIN POSSIBLE AREAWIDE 08Z-13Z EACH MORNING THU AND FRI. A STRONG FRONTAL SYSTEM WILL BRING A GOOD CHANCE OF SUB-VFR CONDITIONS WITHIN WIDESPREAD SHOWERS/STORMS FRI AFTERNOON INTO FRI NIGHT. HIGH PRESSURE WILL THEN BUILD IN YIELDING VFR CONDITIONS SAT. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES...
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DENSE FOG ADVISORY UNTIL 10 AM EDT THIS MORNING FOR NCZ007>011-021>028-038>043-073>077-083>086-088.
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&& $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...DJF AVIATION...HARTFIELD

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