Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 261800 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 100 PM EST MON JAN 26 2015 .SYNOPSIS... LOW PRESSURE WILL WEAKEN AS IT MOVES INTO THE CENTRAL APPALACHIANS THIS MORNING...WHILE ANOTHER AREA OF LOW PRESSURE WILL DEVELOP AND QUICKLY INTENSIFY OFF THE MID-ATLANTIC COAST LATER TODAY. DRY HIGH PRESSURE BUILDS INTO OUR AREA FROM THE WEST THROUGH WEDNESDAY. A COLD FRONT IS EXPECTED TO CROSS THE REGION LATE THURSDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1245 PM EST MONDAY...CURRENT FCST REMAINS ON TRACK THEREFORE NO MAJOR CHANGES NEEDED WITH THIS UPDATE. DID TWEAK TEMPERATURE AND DEWPOINT TRENDS ACROSS THE REGION TO REFLECT LATEST OBSERVATIONS. LATEST REPORTS ALONG WITH WEBCAM DEPICTIONS ACROSS THE REGION REMAIN CONSISTENT WITH CURRENT ADVISORY PRODUCT AS THE BULK OF ANY SNOW ACCUMULATION REMAINS ALONG THE HIGHER PEAKS AND RIDGETOPS ABOVE 3500FT. WILL CONTINUE TO MONITOR CONDITIONS ALONG WITH ANALYSIS OF LATEST GUIDANCE AS IT PERTAINS TO EXTENSION/EXPANSION OF CURRENT ADVISORY PRODUCT INTO THE EVENING. PREVIOUS DISCUSSION... AT 330 AM EST MONDAY...AND EAST COAST TROUGH WILL SLOWLY PROGRESS OVER THE EASTERN SEABOARD TODAY AND TONIGHT. AN UPPER LOW WILL MOVE ACROSS THE SOUTHERN APPALACHIANS TODAY. AN ASSOCIATED SHORTWAVE WILL CROSS THE WESTERN CAROLINAS AND NE GA THIS MORNING. THE SHORTWAVE WILL BE FOLLOWED BY SEVERAL SLUGS OF CHANNELED VORTICITY...WITH A NOTABLE ONE CROSSING THE AREA THIS EVENING...AND ANOTHER EQUALLY IMPRESSIVE ON ARRIVING TOWARD DAWN. A COLD FRONT WILL CROSS OUT AREA EARLY TODAY...PRECEDED AND ACCOMPANIED BY LIGHT PRECIPITATION. THE BEST PRECIPITATION COVERAGE AND INTENSITY IS EXPECTED TO BE IN NC...CLOSER TO THE TRACK OF THE UPPER LOW. SNOW LEVELS ARE EXPECTED TO LOWER IN THE NC MOUNTAINS TOWARD DAYBREAK...REMAINING RATHER LOW AS COLD ADVECTION BEHIND THE FRONT SETS UP. SOME VALLEY FLOORS WILL REMAIN BELOW SNOW LEVELS. SNOW MAY EVEN MIX IN WITH RAIN IN A FEW PORTIONS OF THE NORTHERN NC FOOTHILLS AND PIEDMONT THIS MORNING...BUT THIS SNOW SHOULD BE BRIEF...AND NOT ACCUMULATE. BY MIDDAY SNOW TOTALS IN THE GREAT SMOKY MOUNTAINS COULD EXCEED THREE INCHES. THE CURRENT WINTER WEATHER ADVISORY WILL BE LEFT IN PLACE. HIGH TEMPERATURES TODAY WILL RUN NEAR NORMAL IN THE LEE OF THE MOUNTAINS...AD AROUND FIVE DEGREES BELOW NORMAL IN THE MOUNTAINS. BY MIDDAY LOW LEVEL WINDS VEER TO NW BEHIND THE FRONT AND SET UP A TRUE NW FLOW SNOW EVENT IN THE NC MOUNTAINS. SNOW LEVEL WILL LOWER TO VALLEY FLOORS TONIGHT...BUT THE SNOW ZONE WILL RETREAT CLOSER TO THE TN BORDER. WITH THE UPPER LOW DEPARTING...AND MOISTURE OVERNIGHT RATHER SHALLOW...ADDITIONAL ACCUMULATIONS ARE EXPECTED REMAIN UNDER TWO INCHES ALONG THE TN BORDER. LOW TEMPERATURES TONIGHT WILL RUN A FEW DEGREES BELOW NORMAL AS POST FRONTAL WINDS KEEP THE LOWER ATMOSPHERE MIXED...PARTIALLY OFFSETTING COLD ADVECTION. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM MONDAY...NORTHWEST FLOW SNOW POTENTIAL WILL LINGER INTO TUESDAY. THE HIGHEST POPS (SOLID CHANCE) WILL RESIDE NEAR THE SMOKIES...AS SHORT TERM GUIDANCE DEPICTS ONLY VERY SHALLOW UPSLOPE MOISTURE FROM ROUGHLY THE FRENCH BROAD VALLEY NORTHEAST. ADDITIONAL ACCUMS OF AROUND AN INCH ARE POSSIBLE...MAINLY ACROSS THE HIGHER ELEVATIONS...BEFORE THE SNOW TAPERS OFF WITH DEPLETING MOISTURE BY TUE EVENING. AFTER A CHILLER-THAN-NORMAL TUE...THE REMAINDER OF THE SHORT TERM PERIOD WILL BE DRY WITH NEAR CLIMO TEMPS...AS A SHIRT WAVE RIDGE PROGRESSES THROUGH AND FLATTENS THE EASTERN LONG WAVE TROUGH. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 310 AM MONDAY...A CLIPPER (OR DUO OF CLIPPERS) WILL MOVE RAPIDLY FROM THE UPPER MISS VALLEY TO THE MID-ATLANTIC IN THE EARLY PART OF THE MEDIUM RANGE. ALTHOUGH BOTH THE GFS AND THE ECMWF FEATURE TWO WAVES...THE EC SHEARS THE FIRST ONE OUT...WHILE THE GFS MAINTAINS A RATHER STRONG LEAD WAVE. THIS IS PROBABLY WHY IT SPREADS LIGHT PRECIP INTO THE FORECAST AREA SEVERAL HOURS EARLIER THAN THE ECMWF. GRADUALLY INCREASING POPS WILL BE ADVERTISED THROUGHOUT THURSDAY...PEAKING AT 20-40 PERCENT ACROSS THE NORTHWEST HALF OF THE AREA BY THE END OF THE DAY. WITH THIS TIMING...THE PRIMARY P-TYPE WOULD BE RAIN...ALTHOUGH SOME SNOW WILL BE POSSIBLE AT THE HIGH ELEVATIONS. AS COLD ADVECTION OVERSPREADS THE AREA...A BRIEF PERIOD OF SNOW COULD FALL AT THE VALLEY FLOORS THU NIGHT BEFORE THE PRECIP COMES TO AN END (AS MORE OF A TYPICAL NW FLOW EVENT). FRIDAY AND FRIDAY NIGHT SHOULD BE DRY AND COOL AS THE EASTERN TROUGH REASSERTS ITSELF. HOWEVER...THE BOTTOM DROPS OUT OF FORECAST CONFIDENCE OVER THE WEEKEND...AS THERE ARE SIGNIFICANT DISCREPANCIES AMONG THE GLOBAL MODELS REGARDING THE TIMING OF NORTHERN STREAM SHORT WAVE FEATURES...AND THE EVOLUTION OF A TROUGH/UPPER LOW ACROSS THE FOUR CORNERS REGION. THE RESULT IS A DIFFERENCE IN TIMING OF AROUND 36 HOURS IN TERMS OF PRECIP CHANCES ASSOCIATED WITH DEVELOPING BAROCLINIC ZONE ACROSS THE SOUTHEAST STATES. TOKEN SLIGHT CHANCE POPS WERE INHERITED FROM SAT NIGHT THROUGH SUNDAY...MAINLY ACROSS THE WESTERN HALF OF THE AREA...AND CONSIDERING THE HIGH LEVEL OF UNCERTAINTY...OPTED TO LEAVE THIS ALONE FOR NOW. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. NORTHWEST WINDS WILL INCREASE THIS AFTERNOON WITH GUSTS SUBSIDING INTO THE EARLY EVENING AS THE PRESSURE GRADIENT AND MIXING RELAX. LOW VFR CIGS WILL PERSIST THROUGH MIDDAY BEFORE INCREASING SLIGHTLY INTO THE 6-8KFT RANGE AROUND 21Z. MID LEVEL SCT DECK IS FCST THROUGH MUCH OF THE OVERNIGHT AHEAD OF AN APPROACHING SHORTWAVE IMPULSE AND ITS ASSOCIATED MOISTURE. THUS...THE MID LEVEL SCT DECK IS PROGGED TO THICKEN WITH CIGS IN THE 10KFT RANGE POSSIBLE AROUND DAYBREAK TUESDAY LASTING THROUGH MID MORNING BEFORE SCT OUT ONCE AGAIN. WINDS WILL REMAIN NORTHERLY THROUGH THE REMAINDER OF THE PERIOD WITH SPEEDS GENERALLY LESS THAN 5-7KTS. ELSEWHERE...VFR CIGS AND GUSTY WINDS WILL HIGHLIGHT THIS TAF CYCLE...ESPECIALLY AT KAVL WHERE VALLEY CHANNELING COULD YIELD GUSTS IN EXCESS OF 25KTS. ALSO AT KAVL...LOW VFR...AND POSSIBLE HIGH LEVEL MVFR CIGS WILL PREVAIL THROUGH MUCH OF THE TAF CYCLE DUE TO UPSTREAM NORTHWEST FLOW SNOW SHOWERS ALONG THE TN LINE. THUS...TAF FEATURES LOW VFR DETERIORATING TO MVFR JUST AFTER MIDNIGHT. WOULD NOTE THAT CONFIDENCE IN THE MVFR CIGS REMAINS RATHER LOW. OTHERWISE...GUSTY WEST TO NORTHWEST WINDS WILL PREVAIL THROUGH SUNSET AT ALL OTHER TAF SITES BENEATH SCT MID LEVEL CIGS. A SECOND ROUND OF MID LEVEL CIG FORMATION IS PROGGED AS UPSTREAM SHORTWAVE IMPULSE AND ASSOCIATED CHANNELED VORTICITY SLIDE INTO THE REGION JUST BEFORE DAYBREAK. THUS TAFS FEATURE BKN CIGS AROUND 8-10KFT BEFORE SCT AFTER SUNRISE. OUTLOOK...A SERIES OF CLIPPER SYSTEMS WILL BRING PERIODIC CHANCES FOR SNOW SHOWERS...MAINLY TO THE MOUNTAINS THROUGH THE WEEK. MOST OF THESE SNOW SHOWERS WILL REMAIN WEST AND NORTH OF KAVL...BUT BRIEF PERIODS OF RESTRICTIONS AND SNOW SHOWERS CANNOT BE RULED OUT THERE. OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED. CONFIDENCE TABLE... 18-24Z 00-06Z 06-12Z 12-18Z 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 HIGH 100% 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 4 PM EST THIS AFTERNOON FOR NCZ051-052-058-059. SC...NONE. && $$ SYNOPSIS...JDL NEAR TERM...CDG/JAT SHORT TERM...JDL LONG TERM...JDL AVIATION...CDG

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