Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160731 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 331 AM EDT TUE SEP 16 2014 .SYNOPSIS...A COLD FRONT APPROACHING THE REGION FROM THE WEST TONIGHT WILL TRACK SLOWLY SOUTHWARD THROUGH THE CAROLINAS TODAY AND TONIGHT. THE FRONT WILL GRADUALLY MOVE OFFSHORE THE SOUTHEAST COAST ON WEDNESDAY AND THURSDAY AS HIGH PRESSURE STRENGTHENS OVER THE GREAT LAKES AND EXTENDS SOUTHWARD THROUGH THE MID ATLANTIC. && .NEAR TERM /THROUGH TONIGHT/... AS OF 330 AM TUESDAY... TODAY...WEAK MID-UPPER LEVEL DISTURBANCE EXITING THE REGION EARLY THIS MORNING. PATCHES OF LIGHT RAIN OR SHOWERS SHOULD CONTINUE TO DECREASE IN COVERAGE/INTENSITY THROUGH DAYBREAK. ABUNDANT LOW LEVEL MOISTURE SHOULD RESULT IN THE FORMATION OF A LOW CLOUD DECK BY DAYBREAK. WEAK SUBSIDENCE IN THE WAKE OF THIS EXITING FEATURE COMBINED WITH A DOWNSLOPE COMPONENT TO THE 925-850MB WIND AFTER 12Z SHOULD AID TO DIMINISH/DISSIPATE THE WIDESPREAD LOW CLOUDS BY LATE MORNING-MID DAY. HEATING OF THE ATMOSPHERE IN COMBINATION WITH RESIDUAL MOISTURE AND THE APPROACH OF ANOTHER MID-UPPER LEVEL DISTURBANCE SHOULD TRIGGER SCATTERED SHOWERS-ISOLATED THUNDERSTORMS. LATEST ROUND OF WRF MODEL RADAR PRESENTATIONS ALONG WITH THE HRRR FAVOR INITIAL DEVELOPMENT IN THE WESTERN PIEDMONT AROUND MID AFTERNOON. THE 00Z GFS (AND MORE SO THE 00Z NAM) INDICATE SLIGHT INSTABILITY OVER THE WESTERN PIEDMONT ALONG WITH SOME BULK SHEAR OF SUFFICIENT MAGNITUDE (25-30KTS) TO ALLOW FOR SOME LOOSELY ORGANIZED CONVECTION. SOME WRF MODELS SUGGEST BROKEN BAND OF CONVECTION MAKING IT INTO THE TRIANGLE REGION BEFORE WEAKENING/DISSIPATING. CONSIDERING THE LACK OF RADAR ECHOES UPSTREAM ASSOCIATED WITH THE NEXT DISTURBANCE...NOT READY TO INCREASE ANY MORE THAN CURRENT 20-40 PERCENT. HOWEVER...HAVE SHIFTED POP EMPHASIS MORE TO THE WESTERN PIEDMONT RATHER THAN THE SOUTHERN COASTAL PLAIN DUE TO BETTER PROXIMITY OF UPPER LEVEL SUPPORT. MOS GUIDANCE CONTINUES TO ADVERTISE MAX TEMPS SOLIDLY IN THE MID 80S. THESE TEMPS ACHIEVABLE IF LOW CLOUDS DEPART/DISSIPATE PRIOR TO 15Z AND SCATTERED CONVECTION HOLDS OFF UNTIL MID AFTERNOON. FAVOR MAX TEMPS SLIGHTLY COOLER THAN MOS (LOWER 80S NW TO MID 80S ELSEWHERE). TONIGHT...SCATTERED CONVECTION WILL GRADUALLY WEAKEN WITH LOSS OF HEATING AND EXITING OF MID LEVEL DISTURBANCE. STILL...COULD SEE A FEW SHOWERS PERSIST PAST MIDNIGHT TOT EH EAST-SOUTH OF RDU. CLOUDINESS AND LACK OF APPRECIABLE LOW LEVEL CAA SUGGEST MIN TEMPS A FEW DEGREES WARMER THAN EARLIER THINKING. MIN TEMPS LOW-MID 60S. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 330 AM TUESDAY... WEDNESDAY...ABUNDANT LOW LEVEL MOISTURE TRAPPED BENEATH A LOW LEVEL INVERSION SHOULD RESULT IN EXTENSIVE CLOUDINESS OVER MOST OF THE REGION WEDNESDAY MORNING...AND POTENTIALLY LINGERING INTO THE AFTERNOON ACROSS THE PIEDMONT. (THIS MAY BE CLASSIFIED AS A HYBRID OR INSITU DAMMING EVENT THOUGH PARENT HIGH RELATIVELY WEAK AND QUITE TRANSITORY). IF EXTENSIVE CLOUDS DO LINGER PAST MID DAY ACROSS THE PIEDMONT...THIS MAY CREATE A DIFFERENTIAL HEATING BOUNDARY BETWEEN THE PIEDMONT AND THE SANDHILLS/SOUTHERN COASTAL PLAIN. THE APPROACH OF YET ANOTHER DISTURBANCE IN THE WEST-NW FLOW ALOFT INTERACTING WITH THIS FEATURE MAY TRIGGER MORE SCATTERED CONVECTION...MAINLY OVER THE SE THIRD OF OUR FORECAST AREA. THE LOW LEVEL STABLE AIR MASS SUGGEST MAINLY PATCHY STRATIFORM RAIN OVER THE NORTHERN PIEDMONT (OR ELEVATED SHOWERS. SINCE LEANING TOWARD MORE CLOUDINESS ACROSS THE PIEDMONT...HAVE LOWERED MAX TEMPS A COUPLE OF DEGREES BUT RAISED MAX TEMPS TO NEAR/ABOVE 80 OVER THE SE COUNTIES. CONTINUED CYCLONIC FLOW ALOFT WILL MAINTAIN CLOUDINESS WEDNESDAY NIGHT ALONG WITH A SMALL THREAT FOR SHOWERS...MAINLY EAST OF HIGHWAY 1. MIN TEMPS SEVERAL DEGREES COMPARED TO THE PREVIOUS NIGHT. MIN TEMPS UPPER 50S NW TO LOWER 60S SE. && .LONG TERM /THURSDAY THROUGH MONDAY/...
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AS OF 330 AM TUESDAY... THE MEDIUM RANGE WILL FEATURE A LONGWAVE TROUGH THAT WILL MOVE OFFSHORE THE EAST COAST THU AND CONSEQUENTLY YIELD TO RISING HEIGHTS ALOFT AS A FLAT MID LEVEL RIDGE RIDGE BRIEFLY BUILDS EAST FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY FRI-SAT. THE RE-ESTABLISHMENT OF A WESTERN NOAM RIDGE WILL THEN RESULT IN DOWNSTREAM TROUGH AMPLIFICATION FROM SOUTH-CENTRAL CANADA TO THE EAST-CENTRAL US SUN- MON...THE LEAD SHORTWAVE TROUGH OF WHICH WILL INCLUDE THE REMNANTS OF TROPICAL STORM ODILE. MEANWHILE AT THE SFC...A CANADIAN-SOURCE SFC HIGH (AROUND 1030 MB) WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES AND RIDGE SOUTH/SOUTHWESTWARD IN DAMMING ORIENTATION EAST OF THE APPALACHIANS THU THROUGH THE WEEKEND...FOLLOWED BY A COLD FRONTAL PASSAGE - DRIVEN BY THE AFOREMENTIONED RE-AMPLIFICATION OF THE LONGWAVE TROUGH INTO THE EAST-CENTRAL US - ON MON. THE RESULT WILL BE A RELATIVELY PROLONGED PERIOD OF EAST TO NORTHEAST LOW LEVEL FLOW AND ASSOCIATED BELOW NORMAL TEMPERATURES... TEMPERED FURTHER BY PERIODS OF BKN MULTI-LAYERED CLOUD COVER...THROUGH EARLY THIS WEEKEND. THE RELATIVE GREATEST CLOUD COVERAGE WILL LINGER THU (FROM WED NIGHT)...WHEN A LINGERING CHANCE OF SHOWERS WILL ALSO REMAIN...MAINLY OVER THE COASTAL WHERE A DEPARTING H85 WAVE/TROUGH WILL AUGMENT WEAK FORCING ALOFT ATTENDING A PAIR OF SHORTWAVE TROUGHS FORECAST TO CROSS THE CAROLINAS AND MIDDLE ATLANTIC THROUGH MID-LATE THU AFTERNOON. UNDER ASSOCIATED VARIABLY CLOUDY SKY COVER...WITH RELATIVE GREATEST COVERAGE EAST...TEMPERATURES SHOULD FALL ABOUT A CATEGORY OR SO SHY OF WHAT FULL SUN THICKNESSES OF AROUND 1385 METERS WOULD OTHERWISE SUPPORT. COOL AGAIN OVERNIGHT WITH DEEP LAYER DRYING/FALLING PRECIPITABLE WATER VALUES TO AROUND AN INCH...AS THE AFOREMENTIONED MID LEVEL RIDGE EXPANDS EASTWARD AND CAUSES - LOWS MIDDLE 50S TO AROUND 60. OTHERWISE...THE INCREASING INFLUENCE OF THE RIDGING AT THE SFC AND ALOFT SHOULD PROMOTE DRY CONDITIONS FRI-SUN...THOUGH WITH TEMPERATURES MODERATING ONLY SLOWLY THROUGH THE 70S...TO AROUND 80 DEGREES BY SUN. THE PASSAGE OF THE SFC COLD FRONT EARLY NEXT WEEK SHOULD THEN SUPPORT A CHANCE OF SHOWERS IN CENTRAL NC ON MON. ONCE THE INHERENT D7 TIMING DIFFERENCES ARE IRONED OUT...A SLIGHT CHANCE OF THUNDER MAY BE INTRODUCED WITH LATER FORECASTS IF IT APPEARS FAVORABLE DIURNAL TIMING OF THE FRONTAL PASSAGE WILL OCCUR.
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 140 AM TUESDAY... AVIATION CONDITIONS AT 0530Z VARY FROM VFR TO MVFR ACROSS CENTRAL NC. A DETERIORATING TEND ANTICIPATED THROUGH 10Z WITH IFR/LIFR CEILINGS HIGHLY PROBABLE AND WIDESPREAD MVFR VISIBILITY DUE TO FOG. THE ADVERSE AVIATION CONDITIONS SHOULD LINGER THROUGH 14Z WITH AN IMPROVEMENT TO VFR CONDITIONS MOST LOCATIONS BY 16Z. SURFACE WINDS WILL BE LIGHT AND VARIABLE...BECOMING NORTH NORTHWEST AT 5KTS OR LESS AFTER 14Z AS A WEAK COLD FRONT DRIFTS ACROSS THE REGION. PATCHES OF LIGHT RAIN WILL OCCUR AHEAD OF THIS FEATURE. LATER THIS AFTERNOON...ISOLATED SHOWERS AND POSSIBLY A THUNDERSTORM MAY OCCUR...MAINLY IN THE VICINITY OF KFAY. VFR CONDITIONS ANTICIPATED TONIGHT THROUGH WEDNESDAY WITH A BRIEF PERIOD OF MVFR CEILING/VISIBILITY POSSIBLE EARLY WEDNESDAY MORNING. THE PERIOD THURSDAY THROUGH SATURDAY APPEARS TRANQUIL WITH MAINLY VFR CONDITIONS. A BRIEF INSTANCE OF MVFR CEILING OR VISIBILITY MAY OCCUR EACH MORNING...MAINLY IN THE VICINITY OF KRWI AND KFAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS/VINCENT NEAR TERM...WSS SHORT TERM...WSS LONG TERM...MWS AVIATION...WSS

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