Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 270330 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 1030 PM EST WED NOV 26 2014 .SYNOPSIS... AN UPPER LEVEL SYSTEM WILL CROSS WESTERN NORTH CAROLINA EARLY THURSDAY. DRY HIGH PRESSURE WILL RETURN FRIDAY AND LINGER INTO THE WEEKEND. EXPECT A COLD FRONT TO SLOWLY CROSS OUR REGION FROM THE NORTH EARLY NEXT WEEK. && .NEAR TERM /THROUGH THURSDAY/... AS OF 930 PM...CLOUDINESS AND LIGHT PRECIP WERE SPREADING ACROSS THE MTNS FROM THE WEST. SOME OTHER LIGHT PRECIP WAS MOVING OVER NE GEORGIA AND INTO THE WRN PART OF THE UPSTATE. THE FCST HAS A FAIRLY DECENT HANDLE ON THIS EVOLUTION...ALTHO THE POP WAS MOVED EAST TOO QUICKLY. THAT WILL BE MODIFIED A BIT. TEMPS WERE ALSO GENERALLY RUNNING A BIT WARMER THAN FCST...WHICH MIGHT KEEP SOME OF THE INITIAL PRECIP FALLING AS LIQUID UNTIL COOLER TEMPS MOVE IN LATE TONIGHT. REMAINDER OF PREVIOUS DISCUSSION... THE FORECAST MODELS AGREE FAIRLY WELL IN BRINGING A STRONG BUT CHANNELED VORTICITY MAXIMUM WITH THIS WAVE THROUGH THE REGION OVERNIGHT...WITH MOIST NW FLOW DEVELOPING IN IT/S WAKE. THE DEEP LAYER QG FORCING SHOULD BE MAXIMIZED MAINLY AROUND 06Z TO 09Z...AND HAVE THE GREATEST IMPACT ACROSS WRN NC. THERE IS ALSO FAIRLY GOOD CONSENSUS THAT THE THERMAL PROFILES WILL WET BULB DOWN TO SUPPORT SNOW ACROSS THE MTNS...AND EVEN INTO THE LOWER VALLEYS...DURING THE EARLY MORNING HOURS. MOISTURE SHOULD BE JUST DEEP ENOUGH TO SUPPORT SNOW CRYSTAL GROWTH...BUT THAT MAY NOT EVEN BE AN ISSUE IF CONVECTIVE SHOWERS FORM AS A POOL OF 7 TO 8 DEG C/KM LAPSE RATES CROSSES THE REGION OVERNIGHT. THIS INSTABILITY...ALONG WITH A +2 PV UNIT SATURATED GEOSTROPHIC EPV MAX...MAY WELL PERMIT SOME SNOW SHOWERS TO BREAK CONTAINMENT EAST OF THE BLUE RIDGE EARLY THU MORNING. BRIEF SNOW SHOWER ACTIVITY WILL THUS BE POSSIBLE ACROSS THE INTERSTATE 40 CORRIDOR INTO THE PIEDMONT. HOWEVER...THE DURATION OF THIS ACTIVITY SHOULD BE BRIEF ENOUGH FOR LITTLE TO NO ACCUMULATIONS TO DEVELOP WITH MINS GENERALLY IN THE MID 30S. THE PRECIPITATION FOCUS WILL THEN STEADILY SHIFT BACK TO THE WRN NC MTN COUNTIES NEAR THE TN BORDER THU MORNING AS A MORE TRADITIONAL NW UPSLOPE FLOW SNOW SITUATION SETS UP. ANTICIPATE THE DEEPEST SFC TO 850 MB MOISTURE THROUGH 18Z...WITH UPSLOPE MOISTURE GRADUALLY WANING THROUGH THU AFTN. THE CURRENT WINTER WEATHER ADVISORY LOOKS WELL PLACED. BREEZY TO WINDY CONDITIONS WILL DEVELOP IN THE HIGHER ELEVATIONS DURING THE PEAK COLD ADVECTION THU...AS THE PRES GRADIENT TIGHTENS BEHIND THE DEPARTING WAVE. EXPECT CHILLY 30S TO LOWER 40S MAXES IN THE MTNS...BUT LOWER 50S ARE MORE LIKELY IN THE EVENTUAL DOWNSLOPE ACROSS THE FOOTHILLS/PIEDMONT. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... AT 230 PM EST WEDNESDAY...ON THURSDAY EVENING...A DEAMPLIFYING UPPER TROUGH AXIS WILL BE NEAR THE EAST COAST...WHILE A RIDGE WILL BE UPSTREAM NEAR THE WEST COAST. A CHANNELED UPPER VORT LOBE ROUNDING THE BASE OF THE TROUGH WILL BE OVER CENTRAL NC...MOVING AWAY FROM OUR AREA. THE UPPER TROUGH WILL CONTINUE TO DEAMPLIFY ON FRIDAY AS THE TROUGH AXIS MOVES OFF THE EAST COAST...WHILE WEAK SHORTWAVE ENERGY MOVES ACROSS OUR AREA FROM THE NW. BY SATURDAY A NEARLY ZONAL FLOW WILL EXIST OVER THE SOUTHERN TIER OF STATE BY SATURDAY. AT THE SURFACE...SOME LINGERING NW FLOW SNOW SHOWERS WILL PERSIST ALONG THE TN BORDER THURSDAY NIGHT IN THE PRESSURE GRADIENT BETWEEN A DEPARTING COASTAL LOW AND HIGH PRESSURE IN THE MS RIVER VALLEY. ACCUMULATIONS WITH THIS DIMINISHING ACTIVITY WILL BE MINIMAL. THE HIGH PRESSURE ARRIVES ON FRIDAY...WHEN THE MODELS SUGGEST SOME UPPER LEVEL CLOUD COVER SPREADING OVER THE MOUNTAINS FORM THE WEST. THIS CLOUD COVER WILL EXTEND EAST ACROSS MOST OF THE AREA BY FRIDAY EVENING...GRADUALLY MOVING NORTH OF THE AREA BY LATE SATURDAY. TEMPERATURES WILL RUN AROUND 12 DEGREES TO SO BELOW NORMAL ON THURSDAY NIGHT THROUGH FRIDAY NIGHT AS THE COOL HIGH PRESSURE ARRIVES...DESPITE RISING HEIGHTS ALOFT. BY SATURDAY...HIGH TEMPERATURES WILL RISE TO WITHIN 3 DEGREES OR SO OF NORMAL AS WARM ADVECTION SETS UP ON THE BACK SIDE OF THE SURFACE HIGH AND HEIGHTS ALOFT CONTINUE TO RISE. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... AS OF 215 PM EST WEDNESDAY...A WEAK UPPER RIDGE AXIS WILL CROSS THE REGION SAT NIGHT THROUGH SUN...WITH A WEAK POSITIVELY TILTED UPPER TROUGH PASSING OVERHEAD ON TUE. ANOTHER WEAK UPPER TROUGH IS FORECAST TO CROSS THE REGION BY WED. AT THE SURFACE...HIGH PRESSURE CENTERED OVER THE WESTERN ATLANTIC WILL CONTINUE TO RIDGE WESTWARD INTO THE FORECAST AREA SAT NIGHT THROUGH AT LEAST MONDAY BRINGING MOSTLY DRY CONDITIONS WITH GOOD WAA SWLY FLOW TO OUR CWA. MEANWHILE...A SURFACE COLD FRONT EXTENDING FROM THE GREAT LAKES REGION TO THE WESTERN GULF SAT NIGHT WILL SLOWLY PUSH SOUTHEASTWARD INTO THE SOUTHERN APPALACHIANS THROUGH MON NIGHT. HENCE...HAVE INHERITED DRY WEATHER SAT NIGHT AND SUN FOR MOST LOCATIONS. POPS THEN RAMP UP INTO THE 20/30S OVER THE MTNS ZONES ON MONDAY AS THE FRONT REACHES THE TN BORDERLINE. THE FRONT WILL THEN SLIP TROUGH THE FORECAST AREA MON NIGHT WITH A COLD AIR DAMMING SETTING UP BY TUE AS A CANADIAN HIGH PRESSURE OVER THE GREAT LAKES REGION SLIDES EAST INTO THE NORTHEAST STATES. POPS REMAIN ON THE LOW SIDE GIVEN THE LACK OF DEEP MOISTURE/UPPER FORCING. WED...THE NEW 12Z ECMWF INDICATES THAT ANOTHER COLD FRONT WILL APPROACH FROM THE NW AND CROSSES THE AREA WED NIGHT INTO THU MORNING WHILE THE GFS KEEPS THE CAD THRU THE PERIOD. GIVE THE UNCERTAINTY...HAVE KEPT THE POPS IN THE SLIGHT CHANCE RANGE. TEMPERATURES WILL BE AROUND 2-5 DEGREES ABOVE NORMAL SUN/MON AND NEAR NORMAL TUE/WED. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... AT KCLT...VFR THRU THE PERIOD. SOME HIGH BASED STRATOCU WILL LINGER ACROSS THE PIEDMONT THRU THE MIDDLE PART OF THE EVENING. A DYNAMIC SHORT WAVE IS EXPECTED TO MOVE THROUGH OVERNIGHT...WITH MAINLY A MID LEVEL CEILING PER UPSTREAM OBSERVATIONS. MODEL GUIDANCE SHOWS LIGHT PRECIP ACCOMPANYING THE PASSAGE OF THE SHORT WAVE DURING THE EARLY MORNING HOURS. THE BETTER CHANCE FOR LIGHT PRECIP WILL BE TO THE N OF THE TERMINAL. HAVE NOT INCLUDED PRECIP IN THE TAF AT THIS TIME BECAUSE THE CHANCE IS TOO LOW. IF PRECIP DOES FALL...IT SHOULD BE IN FORM OF RAIN...BUT A WET SNOW CHANCE WOULD BE NOT FAR TO THE N. WINDS HAVE BACKED AROUND TO SE TO S AHEAD OF THE SHORT WAVE FEATURE...AND SHOULD GRADUALLY VEER AROUND TO S OR SW THROUGH THE REST OF THE MORNING ON THURSDAY. A COLD FRONT SHOULD CROSS THE REGION IN THE LATE MORNING WHICH WILL BRING THE WIND DIRECTION AROUND TO NW. TIMING COULD BE AS EARLY AS 13Z AND AS LATE AS 17Z... SO THE 16Z PASSAGE FROM THE EARLIER TAF WAS KEPT. CLOUDS SHOULD SCATTER OUT THEN. ELSEWHERE...VFR THRU THE PERIOD AT MOST TERMINALS. THE BEST CHANCE FOR A CEILING RESTRICTION WILL BE AT KAVL AND KHKY...WHERE THE MODEL GUIDANCE SHOWS THE BEST CHANCE FOR PRECIP. SOME OF THE PRECIP COULD FALL AS WET SNOW. THE CHANCE REMAINS TOO LOW TO INCLUDE AT THIS TIME...BUT FUTURE AMENDMENTS COULD ADD IT IN IF CONFIDENCE GOES UP. OUTLOOK...DRY HIGH PRESSURE WILL SET UP OVER THE AREA FRIDAY THROUGH THE WEEKEND. A COLD FRONT WILL APPROACH FROM THE NORTHWEST EARLY NEXT WEEK. CONFIDENCE TABLE... 03-09Z 09-15Z 15-21Z 21-00Z KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 100% KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAVL HIGH 100% HIGH 100% HIGH 100% HIGH 100% KHKY MED 72% HIGH 100% HIGH 100% HIGH 100% KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAND HIGH 100% HIGH 100% HIGH 100% HIGH 100% THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE) WWW.WEATHER.GOV/GSP/AVIATION_TABLES && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...WINTER WEATHER ADVISORY UNTIL NOON EST THURSDAY FOR NCZ033- 048>052-058-059. SC...NONE. && $$ SYNOPSIS...DEO NEAR TERM...HG/PM SHORT TERM...JAT LONG TERM...JOH AVIATION...PM

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