Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250333 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1033 PM EST WED DEC 24 2014 .SYNOPSIS...
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A WEDGE FRONT AND COLD FRONT WILL MOVE EAST ACROSS CENTRAL NC TONIGHT. HIGH PRESSURE WILL BUILD IN FROM THE SOUTHWEST FOR CHRISTMAS DAY THROUGH SATURDAY.
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&& .NEAR TERM /TONIGHT/...
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AS OF 1030 PM WEDNESDAY... AT 03Z A COLD FRONT WAS ANALYZED ALONG THE EASTERN SLOPES OF THE NC AND VA BLUE RIDGE...WHILE THE SOUTHERN PORTION OF THE FRONT HAD ACCELERATED AROUND THE SOUTHERN RIM OF THE APPALACHIANS (AS IS USUALLY THE CASE) AND EXTENDED FROM FAR WESTERN SC SOUTH THROUGH EAST-CENTRAL GA TO THE EASTERN GOM. MEANWHILE...A WEDGE FRONT EXTENDED FROM CENTRAL NJ SOUTHWEST THROUGH EAST-CENTRAL VA...THE FAR NW NC PIEDMONT - BETWEEN GSO AND INT - TO WEST CENTRAL SC. THE WARM SECTOR...CHARACTERIZED BY SURFACE TEMPERATURES AND DEWPOINTS IN THE LOW-MID 60S AND SSW WINDS WITH OCCASIONAL GUST TO AROUND 25 MPH...HAS CONSEQUENTLY ENVELOPED ALL BUT FORSYTH COUNTY IN THE RAH CWFA. ALOFT...A POWERFUL (170 KT) SW UPPER LEVEL JET OVER THE TN AND OH VALLEYS WAS ANALYZED ON THE EAST SIDE OF A POSITIVELY-TILTED UPPER TROUGH FROM THE GREAT LAKES TO THE SOUTHERN PLAINS...SUGGESTIVE OF A LIFTING TROUGH WITH THE ASSOCIATED STRONGEST HEIGHT FALLS ALOFT (150- 300 METERS/12 HR) POISED TO LIFT TOWARD THE EASTERN GREAT LAKES AND SE CANADA. DESPITE THE WELL-REMOVED-FROM NC STRONGEST FORCING FOR ASCENT...THE COMBINATION OF LOW LEVEL FRONTAL FORCING FROM THE AFOREMENTIONED LOW LEVEL FRONTAL ZONE AND STILL RESPECTABLE MID LEVEL HEIGHT FALLS (50-100 METERS/12 HR) FORECAST TO SPREAD EAST INTO CENTRAL NC - AMIDST A PLUME OF LINGERING DEEP MOISTURE CHARACTERIZED BY 00Z RAOB- OBSERVED PRECIPITABLE WATER VALUES OF 1.25-1.5 INCHES FROM GSO TO MHX - WILL SUPPORT A CONTINUED CHANCE OF RAIN ENDING FROM WEST TO EAST BETWEEN 05-11Z. THE RAIN WILL LIKELY BE MIXED-CHARACTER...WITH SHOWERS DRIVEN BY THE LOW LEVEL FRONTAL ZONES...AND JET-FORCED/MID- HIGH LEVEL SATURATION AND ASSOCIATED LIGHT RAIN/SPRINKLES THAT NWP GUIDANCE SUGGESTS WILL BLOSSOM OVER NC AND VA AND IMMEDIATELY TRAIL OR SLIGHTLY OVERLAP THE PRECEDING SHOWERS. WHILE ASSOCIATED RAINFALL AMOUNTS WILL BE LIGHT OVERALL...A TENTH OR TWO WILL BE POSSIBLE IN ASSOCIATION WITH ANY LOW-TOPPED LINE OF SHOWERS THAT MAY DEVELOP FROM INVOF BOTH THE WEDGE AND COLD FRONTS AS THEY MOVE EAST OVERNIGHT. INDEED...THERE HAS BEEN SOME RECENT INTENSIFICATION OF A THIN AND SHALLOW LINE OF SHOWERS JUST WEST OF CAE DURING THE PAST HOUR...AND THIS TREND OF THE DEVELOPMENT OF A THIN LINE OR TWO OF SHOWERS IN CENTRAL NC IS PROBABLE AS THE EASTERN EDGE OF THE FORCING ALOFT OVERSPREADS THE LOWER FRONTAL ZONES. NO STRONG TO SEVERE WEATHER - AND LIKELY NO THUNDER ALTOGETHER - IS ANTICIPATED... HOWEVER...OWING TO WEAK MID LEVEL LAPSE RATES OF 5.5 C/KM OR LESS AND ASSOCIATED NEGLIGIBLE OBSERVED AND FORECAST INSTABILITY. INITIALLY MILD TEMPERATURES SHOULD COOL POST-FRONTALLY INTO THE MIDDLE 40S WEST TO MIDDLE-UPPER 50S EAST BY MORNING.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 305 PM WEDNESDAY... AS THE COLD FRONT EXITS THE AREA...HIGH PRESSURE WILL BUILD IN FROM THE GULF COAST REGION. GIVEN THE SOURCE OF THE AIRMASS AND WESTERLY FLOW...HIGHS SHOULD BE SLIGHTLY ABOVE NORMAL IN THE MID TO UPPER 50S. WINDS WITHIN THE MIXED LAYER CAP OUT AT AROUND 25-30MPH MIDDAY...SO THERE SHOULD BE SOME GUSTS INTO THE LOWER 20S EARLIER IN THE DAY. OTHERWISE...QUIET WEATHER WILL CONTINUE ON THROUGH THURSDAY NIGHT AS HIGH PRESSURE BUILDS OVERHEAD AND LOWS DIP INTO THE LOW TO MID 30S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 335 PM WEDNESDAY... FOR FRI/FRI NIGHT: CALM AND MOSTLY CLEAR AS SURFACE HIGH PRESSURE DRIFTS OVERHEAD... AND MID LEVEL RIDGING BUILDS ALOFT OVER AND JUST OFF THE SOUTHEAST STATES. THE MID LEVEL AND SURFACE RIDGES WILL SHIFT EAST LATE FRI INTO FRI NIGHT. AS A RESULT OF STRENGTHENING UPPER LEVEL WINDS FROM THE SW INTO THE MIDATLANTIC REGION... HIGH THIN CLOUDS WILL SPREAD IN FRI EVENING/NIGHT. IN ADDITION... INCREASING RETURN FLOW ON THE WEST SIDE OF THE EXITING LOW LEVEL RIDGE WILL BRING A CHANCE OF FOG AND/OR STRATUS LATE FRI NIGHT AS SW WINDS INCREASE IN THE 925-850 MB LAYER. LOW LEVEL THICKNESSES START OUT CLOSE TO NORMAL... ALTHOUGH MUCH OF THIS WARMTH WILL BE CONTAINED BELOW THE SUBSIDENCE INVERSION JUST OFF THE SURFACE. REGARDLESS... GIVEN THE MILD SOURCE REGION OF THE AIR MASS... EXPECT HIGHS ABOUT A CATEGORY ABOVE NORMAL... AND LOWS NEAR TO JUST BELOW NORMAL WITH MINIMAL CLOUD COVER AND LIGHT WINDS. FOR SAT-SUN: AS THE SURFACE HIGH SHIFTS FURTHER OFFSHORE SAT... THE FRONTAL ZONE TO OUR SOUTH IS EXPECTED TO START MOVING NORTHWARD... PUSHING INTO THE NC PIEDMONT BY SUN. THE GFS/ECMWF BEGIN TO SPREAD PRECIP INTO NC FROM THE SW LATE SAT NIGHT BUT ESPECIALLY SUN... A FUNCTION OF THE STRENGTHENING SW FLOW IN THE 850-500 MB LAYER FROM THE NW GULF RIDING UP AND ALONG THE SURFACE FRONTAL ZONE. WITH GOOD MODEL AGREEMENT... WILL SPREAD IN GOOD CHANCE POPS FROM THE SW STARTING EARLY SUN MORNING... AND CONTINUING THROUGH SUN AND SUN NIGHT... AS WEAK MID LEVEL VORTICITY AND A SURFACE LOW TRACK UP ALONG THE FRONT ACROSS WRN AND NRN NC. HIGHS IN THE UPPER 50S TO LOWER 60S BOTH DAYS... LIKELY A LITTLE COOLER SUN AS THE RAIN ARRIVES. LOWS IN THE 40S SAT NIGHT AND MID 40S TO AROUND 50 SUN NIGHT. FOR MON-WED: EXPECT A DROP IN TEMPS AND AT LEAST A COUPLE OF ROUNDS OF LIGHT RAIN DURING THIS PERIOD. THE GFS/ECMWF TAKE THE FRONT BACK SOUTHWARD IN A BACKDOOR FASHION MON... AND THE FRONT SHOULD SETTLE JUST SOUTH OF THE CWA MON NIGHT... AS A PORTION OF EXPANSIVE HIGH PRESSURE CENTERED OVER THE NRN HIGH PLAINS EXTENDS INTO NC FROM THE NORTH. WE MAINTAIN A FAIRLY FLAT SW MID LEVEL FLOW FROM TX TO THE CAROLINAS THROUGH MID WEEK... AS POSITIVELY TILTED LONGWAVE TROUGHING DIGS FROM THE UPPER MIDWEST TOWARD THE DESERT SOUTHWEST. IT APPEARS LIKELY THAT WE`LL KEEP AN OVERRUNNING SW FLOW AT 850 MB UP AND OVER THE SURFACE FRONTAL ZONE... SO WE SHOULD KEEP A COOL AND FAIRLY CLOUDY AND STABLE AIR MASS OVER CENTRAL NC. IT`S DIFFICULT TO TRY TO TIME INDIVIDUAL WEAK PERTURBATIONS IN THIS SORT OF PATTERN THIS FAR OUT IN TIME... SO WILL NEED TO KEEP IN A CHANCE OF RAIN THROUGH THE PERIOD... ALTHOUGH WE SHOULD SEE THE BEST CHANCES ON MON (WITH A MORE PROMINENT WAVE PASSAGE)... AND PERHAPS EARLY WED. EXPECT EARLY-DAY HIGHS MON IN THE MID 50S TO LOW 60S... THEN HIGHS SHOULD DROP TO THE 40S FOR TUE/WED. -GIH && .AVIATION /00Z THURSDAY THROUGH SUNDAY/... AS OF 720 PM WEDNESDAY... PRIMARY AVIATION CONCERNS THIS PERIOD: IFR/LIFR CONDITIONS THROUGH THIS EVENING... AND LOW LEVEL WIND SHEAR POTENTIAL THROUGH THIS AFTERNOON. 24 HOUR TAF PERIOD: VARYING CONDITIONS ACROSS THE CWA THIS EVENING AS DENSE FOG CONTINUES FOR THE TRIAD SITES WITH DENSE FOG VLIFR CONDITIONS UNDER THE COLD AIR DAMMING WEDGE. TO THE EAST...CONDITIONS ARE GENERALLY BETTER BUT LIGHT RAIN WILL CONTINUE FOR EASTERN SITES FOR THE NEXT SEVERAL HOURS. AS THE FRONT WORKS THROUGH THE AREA CONDITIONS WILL BECOME DRIER BUT SOME RESIDUAL ELEVATED INSTABILITY COULD CAUSE LIGHT RAIN TO REDEVELOP OVER THE AREA DURING THE OVERNIGHT HOURS. EVENTUALLY THE COOLER AND DRIER AIRMASS WILL MOVE IN AND CONDITIONS WILL IMPROVE TO VFR AND SHOULD REMAIN THERE THROUGH THE END OF THE TAF PERIOD. AS CONDITIONS IMPROVE...ATTENTION WILL TURN TO THE WINDS WHICH ARE BEGINNING TO GUST NOW IN SOME LOCATIONS TO 15-20 KTS. GUSTING WILL BE EPISODIC OVERNIGHT BUT BE MORE PREVALENT AFTER 15Z ON THURSDAY THROUGH SUNSET. IN ADDITION TO GUSTING...WINDS WILL SHIFT FROM A MORE SOUTHERLY DIRECTION THIS EVENING TO A WEST OR NORTHWESTERLY DIRECTION BY SUNRISE. SOME AFTERNOON CLOUDS NEAR MVFR LEVELS COULD DEVELOP BUT PROBABLY WILL BE SCATTERED IN NATURE. LONG TERM: A SERIES OF STORM SYSTEMS IN THE LONG TERM WILL KEEP THE PATTERN UNSETTLED. THE NEXT CHANCE FOR ADVERSE AVIATION CONDITIONS WILL BE ON SUNDAY AFTERNOON WHEN A SOUTHERN STREAM SYSTEM AFFECTS THE AREA. PERIODS OF SUB-VFR CONDITIONS ARE POSSIBLE THROUGH TUESDAY NIGHT OR WEDNESDAY BEFORE A BRIEF LULL IN THE PRECIPITATION BEFORE ANOTHER STORM MOVES IN FOR THE END OF THE WORK WEEK. && .HYDROLOGIC DISCUSSION /THROUGH FRIDAY/... AS OF 400 PM WEDNESDAY... THERE HAVE BEEN THREE FAIRLY SIGNIFICANT RAINFALL EVENTS OVER CENTRAL NORTH CAROLINA DURING THE PAST TWO WEEKS...WITH HEAVIER RAINFALL AMOUNTS (>1 INCH TOTAL) GENERALLY FROM THE TRIANGLE AND FAYETTEVILLE AREAS EAST TO THE COAST. AS A RESULT...RELATIVE SOIL MOISTURES PRIOR TO THE RAIN OVER THE PAST 36 HOURS WERE UNIFORMLY HIGH THROUGH A 200 CM DEEP COLUMN...WHICH PROMOTES FASTER RUNOFF AS WELL AS A HIGHER PERCENTAGE OF RAINFALL-TO-RUNOFF FROM TODAYS RAIN. WIDESPREAD SIGNIFICANT RAINFALL OF 1.5 TO 2.0 INCHES HAS FALLEN ACROSS THE AREA IN THE PAST 24 HOURS OR SO...WITH SOME AREAS... PARTICULARLY IN WAKE COUNTY... RECEIVING OVER 2 INCHES. ADDITIONAL RAINFALL IS EXPECTED THROUGH THIS EVENING AND POSSIBLY INTO THE EARLY OVERNIGHT HOURS...HOWEVER TOTALS FROM 4 PM THROUGH 3 AM WILL BE MAINLY A QUARTER OF AN INCH OR LESS. THE HIGHEST AMOUNTS ARE EXPECTED ACROSS THE EASTERN HALF OF THE AREA. MANY OF THE MAIN STEM RIVERS IN THE HYDROLOGIC SERVICE AREA HAVE SEEN INCREASES AS A RESULT OF THE RAIN THAT HAS FALLEN YESTERDAY AND TODAY. IN WAKE COUNTY...CRABTREE CREEK IS OUT OF ITS BANKS AT OLD WAKE FOREST RD AND IS LIKELY HIGH IN MOST OTHER PLACES. THE NEUSE RIVER AT CLAYTON IS CURRENTLY IN FLOOD...WITH AT LEAST ONE SECTION OF THE GREENWAY NEAR NC 42 UNDER WATER. THE NEUSE AT SMITHFIELD HAS INCREASED RAPIDLY TODAY AND WILL LIKELY GO ABOVE FLOOD EARLY THIS EVENING. RIVER FLOOD WARNINGS HAVE BEEN ISSUED AT BOTH LOCATIONS. THE NEUSE RIVER AT GOLDSBORO WILL LIKELY FLOOD FRIDAY OR SATURDAY IN RESPONSE TO THE RISES AT THE OTHER TWO LOCATIONS UPSTREAM. OTHER LOCATIONS THAT MAY FLOOD IN THE NEXT FEW DAYS INCLUDE FISHING CREEK AT ENFIELD AND THE TAR RIVER AT TARBORO. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...BLS LONG TERM...HARTFIELD AVIATION...ELLIS HYDROLOGY...BADGETT/KC

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