Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 010804 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 404 AM EDT SAT NOV 1 2014 .SYNOPSIS... A DEEP UPPER LOW PRESSURE SYSTEM WILL CROSS THE AREA FROM THE WEST TODAY. THIS SYSTEM WILL BE ACCOMPANIED BY COLD TEMPERATURES AND VERY WINDY CONDITIONS. DRY AND COLD HIGH PRESSURE WILL RETURN SUNDAY THROUGH EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 3 AM...AN AREA OF LIGHT TO MODERATE PRECIP CONTINUES TO EXPAND OVER UPSTATE SC AND INTO THE NC FOOTHILLS AND WRN PIEDMONT...FOR WHICH THE MODELS SEEM TO HAVE A FAIRLY GOOD HANDLE. WILL INCREASE THE PRECIP PROBABILITY TO CATEGORICAL ACROSS MOST OF THE UPSTATE AND NC FOOTHILLS TO ACCOUNT FOR RADAR TRENDS. WHAT IS TROUBLESOME IS THAT THE KGSP RADAR CONTINUES TO SHOW INTENSIFICATION AS THE AREA OF REFLECTIVITY 40 DBZ AND GREATER EXPANDS RIGHT OVER METRO GREENVILLE...WHILE TEMPS CONTINUE TO FALL INTO THE MID 30S. THAT WILL KEEP WET BULB TEMPS HOVERING RIGHT AROUND THE RAIN/SNOW THRESHOLD FOR THE NEXT FEW HOURS. WILL NOT TAKE MUCH TO DRAG THE FREEZING LEVEL DOWN CLOSE ENUF TO THE SFC TO ALLOW FOR A CHANGEOVER. THIS MIGHT BE HAPPENING ALREADY AS LOW AS 1500 FEET IN ELEVATION...THAT IS TO SAY...ON THE SLOPE OF THE BLUE RIDGE IN SC...AND THE TOP OF PARIS MTN. FORTUNATELY...IF THE PRECIP CHANGES OVER TO SNOW...IT WILL BE WET AND PROBABLY MELT ON CONTACT WITH ROAD SURFACES. WILL EXPAND THE WINTER WX ADVISORY TO INCLUDE RUTHERFORD MTNS/POLK MTNS/GREENVILLE MTNS BASED ON SNOWFALL REPORTS NEAR SALUDA. THIS IS A VERY DYNAMIC SITUATION...AND THE ADVISORY MIGHT HAVE TO BE EXPANDED EVEN FURTHER. THE UPPER LOW SHOULD PASS OVERHEAD THROUGH THE MORNING HOURS WITH ALL MANNER OF LOW/MID/HIGH UPPER FORCING COMING INTO PLAY. HAVE RAISED/EXPANDED THE PRECIP PROBABILITY THROUGH THE MORNING HOURS. CANNOT RULE OUT A CHANGEOVER TO WET SNOW ACROSS THE NC FOOTHILLS/UPSTATE AS THE COLDER AIR SPILLS DOWN FROM THE MTNS. A MIX/CHANGEOVER ACTUALLY APPEARS A BIT LESS OF A POSSIBILITY OVER METRO CLT AS THE MODEL TREND WAS A BIT WARMER THIS MORNING. HOWEVER...AS WE ARE SEEING CURRENTLY OVER GSP...IF THE PRECIPITATION FALLS WITH ENUF INTENSITY...SOME WET SNOW COULD MAKE IT TO THE GROUND. THE UPPER LOW SHOULD PULL A QUICK EXIT OFF TO THE EAST DURING THE MIDDLE PART OF THE DAY...BRINGING THE LOW LEVEL WINDS AROUND TO A N TO NW DOWNSLOPE AFTER 15Z...WHICH SHOULD START TO DIMINISH PRECIP POTENTIAL NEAR THE BLUE RIDGE/WRN UPSTATE. AS THE LOW MOVES AWAY...SOME WRAP AROUND DEFORMATION MAY LINGER OVER THE WRN PIEDMONT INTO THE AFTERNOON...BUT THAT SHOULD ALSO DIE OFF AND MOVE EAST BY LATE AFTERNOON. MEANWHILE...THE MTNS WILL UNDERGO A TRANSITION TO A MORE PURE NW FLOW PRECIP EVENT...WHICH WILL MAINLY BE SNOW. WILL MAINTAIN A HIGH PRECIP CHANCE NEAR THE TN BORDER...AND TAPER IT OFF EASTWARD FROM THERE. WE SHOULD CONTINUE TO DRY OUT EVERYWHERE E OF THE SPINE OF THE APPALACHIANS THIS EVENING AND TONIGHT. HOWEVER...THE NW FLOW SNOW WILL CONTINUE INTO TONIGHT ALONG THE TN BORDER. THIS MAY REQUIRE EXTENDING THE WINTER STORM WARNING THROUGH THIS EVENING. WIND GUSTS SHOULD ABATE ENUF AROUND SUNSET THAT WE CAN KEEP THE SAME EXPIRATION TIME ON THE WIND ADVISORY. AS FOR THE FREEZE WATCH...FCST LOWS ARE SUCH THAT WE CAN ROLL THAT OVER TO A FREEZE WARNING. THE WARNING WILL HAVE TO BE EXPANDED INTO THE NRN FOOTHILLS OF NC BASED ON THE MIN TEMP FCST. HENDERSON COUNTY NC WILL BE LEFT OUT AS THE FROST/ FREEZE PROGRAM ENDS 1 NOVEMBER AS A MATTER OF POLICY.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM EDT SAT...A DEEP UPPER LOW PRESSURE TROUGH OFF THE CAROLINAS COAST 12Z SUN WILL LIFT NNE INTO THE MAINE COAST BY 00Z MON...LEAVING THE CWA UNDER NWLY FLOW ALOFT ON SUN. H5 HEIGHTS/THICKNESSES RISE CONSIDERABLY BY MON AS AN UPPER RIDGE BUILDS IN FROM THE WEST. THE UPPER RIDGE AXIS IS FORECAST TO REACH OUR REGION BY MON NIGHT. AT THE SURFACE...1030MB SURFACE HIGH WILL BUILD IN FROM THE NW SUN AND BECOMES CENTERED OVER THE SE STATES BY MONDAY. ANY LINGERING NW PRECIP ALONG THE TN BORDER LINE SHOULD TAPER OFF BY SUN MORNING AS DRY AIRMASS MOVES IN. WITH PREVAILING CAA NW FLOW ON SUN...TEMPS SHOULD REMAIN AROUND 10-15 DEGREES BELOW NORMAL. LATEST GUIDANCE SUGGESTS THAT SUB-FREEZING TEMPS ARE EXPECTED OVER MUCH OF THE CWA ON SUN NIGHT. THEREFORE...ANOTHER FREEZE WATCH MAY BE NEEDED OVER EAST OF THE MTNS FOR THIS PERIOD. AS MODIFYING HIGH PRESSURE CENTERED OVER THE REGION SHIFTS EAST THROUGH MONDAY NIGHT...WINDS WILL VEER TO THE SW AND TEMPS SHOULD WARM UP BY MORE THAN 10 DEGREES BY MON AFTERNOON IN ITS WAKE. CONDITIONS SHOULD REMAIN DRY UNDER THE HIGH PRESSURE MON. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 230 AM EDT SAT...LATEST GLOBAL MODELS CONTINUE TO AGREE THAT AN UPPER RIDGE AXIS OVER THE EASTERN STATES WILL SHIFT OFFSHORE BY TUE NIGHT AS A POSITIVELY TILTED UPPER TROUGH APPROACHES FROM THE CENTRAL CONUS. THIS TROUGH IS FORECAST TO CROSS THE EASTERN CONUS BETWEEN WED NIGHT AND THU...OFF THE ATLANTIC COAST BY EARLY FRI. AT THE SURFACE...A MODIFYING HIGH PRESSURE CENTERED OVER THE SE STATES WILL GRADUALLY SHIFT OFFSHORE TUE INTO WED AS A WEAK COLD FRONT APPROACHES FROM THE WEST. THE FRONT SHOULD CROSS THE REGION LATE WED INTO THU...OFF TO OUR EAST BY THU NIGHT. IT STILL APPEARS THAT THE FRONT WILL BE MOISTURE STARVED. HENCE...HAVE INHERITED SLIGHT CHANCE POPS OVER THE PIEDMONT WITH LOW END CHANCE MANLY OVER THE WESTERN ZONES OF THE MTNS WED AFTERNOON THRU THU MORNING. CONDITIONS LOOK DRY THU NIGHT AND FRI AS A COOL HIGH PRESSURE BUILDS IN FROM THE WEST. MODES SUGGEST THAT THERE COULD BE LIGHT NW PRECIP (A MIX OF RAIN AND SNOW) BEHIND THE DEPARTING FRONT ALONG THE TN BORDER THU NIGHT INTO FRI. SO HAVE KEPT SLIGHT CHANCE FOR RN/SN THERE THRU FRI MORNING. TEMPS SHOULD START OUT AROUND 3-5 DEGREES BELOW NORMAL TUE...WARMING UP TO NEAR NORMAL BY WED. TEMPS THEN COOL OFF BY 5-7 DEGREES BY FRI IN THE WAKE OF THE FROPA. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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AT KCLT...ADDITIONAL AREAS OF LIGHT RAIN HAVE DEVELOPED ACROSS THE NRN UPSTATE OF SC AND INTO THE CLT METRO AREA. EXPECT LIGHT RAIN TO CONTINUE FALLING FOR THE BETTER PART OF THE PRE-DAWN HOURS...WHICH IS EXPECTED TO BRING THE CEILING DOWN INTO THE MVFR RANGE NO LATER THAN 10Z. WIND WILL REMAIN N AND WILL STRENGTHEN THROUGHOUT THE MORNING...BECOMING GUSTY ONCE THE SUN RISES AND THE BOUNDARY LAYER DEEPENS ENUF TO TAP INTO SOME HIGHER WIND ALOFT. THE BIG QUESTION THIS MORNING IS THE PRECIP TYPE. THE MODEL TREND ON THE 00Z RUN WAS FOR A SLIGHTLY WARMER AND DEEPER BOUNDARY LAYER. FCST SOUNDINGS NO LONGER SUPPORT SNOW. SFC TEMPS DO NOT FALL BELOW ABOUT 39 DEGREES EVEN ON THE COLDEST MODEL GUIDANCE. FOR THAT REASON...HAVE ELIMINATED THE RAIN SNOW MIX THAT WAS IN THE PREVIOUS TAF. WILL NEVER COMPLETELY RULE OUT SOME WET SNOWFLAKES OR SLEET PELLETS IN THIS TYPE OF SITUATION WITH A VERY DYNAMIC AND COLD CORE UPPER LOW...BUT THE CHANCE IS ONLY SOMETHING LIKE 10 PERCENT...SO IT WAS LEFT OUT OF THE 06Z TAF. WILL EVALUATE AGAIN WHEN THE 03Z SREF GUIDANCE ARRIVES...AND THE REST OF THE FCST IS UPDATED. THE UPPER LOW MOVES OUT QUICK DURING THE MIDDLE PART OF THE DAY. CEILING SHOULD START TO IMPROVE AROUND 17Z AND SHOULD LIFT TO VFR BY MID AFTERNOON. THE LOW CLOUDS MAY SCATTER OUT QUICKER THAN THE TAF INDICATES...BUT CERTAINLY BY AROUND SUNSET...AT WHICH TIME THE WIND GUSTS SHOULD SUBSIDE. ELSEWHERE...KAVL WILL HAVE THE GREATEST IMPACT. ANY PRECIP THAT FALLS SHOULD MAINLY BE IN THE FORM OF SNOW AT KAVL...AND SHOULD BRIEFLY REDUCE VSBY TO MVFR OR IFR RANGE. WENT WITH A TEMPO IFR FOR THE SNOW FOR THE FIRST PART OF THE TAF BASED ON RADAR TREND... AND THIS WILL PROBABLY BE MOVED FORWARD IN TIME WITH EACH SUCCESSIVE AMEND. THE OTHER TAF SITES SHOULD SEE LIGHT RAIN AS COLDER AIR FILTERS IN...PERHAPS MIXING WITH SOME WET SNOW FROM AROUND DAYBREAK TO MID MORNING DURING THE MOST DYNAMIC PART OF THE LOW PASSAGE. THIS WAS INCLUDED AS A TEMPO AT KHKY/KGSP/KGMU...BUT LEFT OUT OF KAND AS DOWNSLOPE SHOULD SUPPRESS PRECIP AROUND THE SAV RIVER BASIN. THE LOW CLOUDS AND PRECIP WILL PERSIST THROUGH THE DAY AT KAVL...BUT MOVE OUT E OF THE MTNS AROUND MIDDAY. OUTLOOK...DRYING HIGH PRESSURE WILL BUILD IN LATE THIS WEEKEND AND CONTINUE THROUGH EARLY NEXT WEEK...BRINGING VFR CONDITIONS.
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&& .GSP WATCHES/WARNINGS/ADVISORIES...
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GA...WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR GAZ010- 017. WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR GAZ010-017. FREEZE WARNING FROM MIDNIGHT EDT TONIGHT TO 9 AM EST SUNDAY FOR GAZ010-017-018-026-028-029. FREEZE WARNING UNTIL 10 AM EDT THIS MORNING FOR GAZ010. NC...WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NCZ053- 059-062>065-501-503-505-507-509. WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NCZ033-035- 048>053-058-059-062>065-501>510. FREEZE WARNING FROM MIDNIGHT EDT TONIGHT TO 9 AM EST SUNDAY FOR NCZ035-056-068-069-501>510. WINTER STORM WARNING UNTIL 8 PM EDT THIS EVENING FOR NCZ033- 048>052-058. FREEZE WARNING UNTIL 10 AM EDT THIS MORNING FOR NCZ033-049-050- 053-063>065. SC...WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ003. WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ001>003. FREEZE WARNING FROM MIDNIGHT EDT TONIGHT TO 9 AM EST SUNDAY FOR SCZ001>008-010>013-019.
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&& $$ SYNOPSIS...JOH NEAR TERM...PM SHORT TERM...JOH LONG TERM...JOH AVIATION...PM

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