Area Forecast Discussion
Issued by NWS Greer, SC

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KGSP 222339 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 639 PM EST MON DEC 22 2014 .SYNOPSIS... A MOIST AIRMASS WILL REMAIN ATOP THE REGION BEFORE A COLD FRONT CROSSES BY WEDNESDAY NIGHT. DRY HIGH PRESSURE WILL ARRIVE FOR CHRISTMAS DAY AND LINGER INTO FRIDAY. ANOTHER COLD FRONT WILL CROSS THE AREA ON SATURDAY...FOLLOWED BY HIGH PRESSURE ON SUNDAY. && .NEAR TERM /THROUGH TUESDAY/... DDHHMM WRKNRT AS OF 635 PM...LIGHT RAIN SHIELD IS MOVING IN A BIT FASTER THAN PROGGED ACROSS THE SW/RN ZONES...SO POPS WERE ADJ UP INTO THE LIKELY/CAT RANGE. LOW END QPF AMOUNTS STILL LOOK GOOD. TEMPS AND TD/S REMAINING NEARLY STEADY STATE IN HIGHLY MOIST ENVIRONMENT...THUS ONLY MINOR TWEAKS NEEDED TO THESE GRIDS. AS OF 225 PM...COLD TEMPS...LOW CLOUDS AND PATCHY DRIZZLE WILL CONTINUE THRU THE AFTERNOON...EXCEPT ALL BUT THE TN BORDER COUNTIES WHERE BREAKS IN THE CLOUDS HAVE LEAD TO RELATIVELY WARM TEMPS. PATCHY RAIN BEGINNING TO SPREAD BACK INTO THE SRN TIER OF THE CWFA AND THIS TREND WILL CONTINUE THRU THE AFTERNOON...WITH SOME SLOW NORTHERLY MOVEMENT OF THE PRECIP. A SERIES OF SHORT WAVES WILL MOVE ACROSS THE AREA IN THE SWLY FLOW AHEAD OF A DEEPENING CENTRAL CONUS TROF TONIGHT AND TUESDAY. AT THE SFC...CAD REGIME WILL REMAIN IN PLACE THRU THE PERIOD AS WELL KEEPING COPIOUS AMOUNTS OF LOW LEVEL MOISTURE ACROSS THE AREA AND NELY SFC FLOW...EXCEPT ACROSS THE MTNS WHERE SLY FLOW PREVAILS. THE LOW LEVEL FLOW WILL REMAIN SLY AS WELL...AND STRENGTHEN TONIGHT INCREASING ISENTROPIC UPGLIDE ACROSS THE AREA. THEREFORE...RAIN SHUD RETURN ALONG WITH THE CONTINUING DRIZZLE THRU THE NITE. EXPECT LOW CLOUDS AND AREAS OF FOG TO CONTINUE OR REDEVELOP AS WELL. CANNOT RULE OUT SOME PATCHY DENSE FOG TOWARD DAYBREAK...BUT LOCATION NOT CERTAIN ENUF TO INCLUDE IN THE FCST ATTM. LOWS WILL BE IN THE 30S FOR ALL BUT THE HIGHER ELEVATIONS OF THE SWRN MTNS AND TN BORDER COUNTIES WHERE THEY ARE OUTSIDE OF THE CAD DOME AND TAP INTO THE WARMING H85 TEMPS. THIS WILL ALSO HELP KEEP PRECIP ALL LIQUID. THERE MAY BE A BRIEF BREAK IN THE BETTER LIFT TUE MORNING...BUT IT RETURNS THRU THE DAY...ALONG WITH DEEPER MOISTURE AND SOME UPPER DIVERGENCE AS A JET STREAK MOVES NORTH INTO THE AREA. EXPECT RAIN AND DRIZZLE TO BECOME WIDESPREAD BY AFTERNOON...ALTHOUGH AREAS OF DRIZZLE WILL LIKELY CONTINUE EVEN WHERE RAIN DIMINISHES. EXPECT ANOTHER COOL DAY UNDER THE CAD. HOWEVER...WOULD NOT BE SURPRISED IF TEMPS WARM A FEW DEGREES ABOVE THE MONDAY READINGS AS THE PARENT HIGH IS SHUNTED EASTWARD AND CAD TAKES ON MORE OF AN IN-SITU PATTERN. THE TN BORDER COUNTIES WILL ONCE AGAIN BE MUCH WARMER THAN AREAS UNDER THE CAD. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... AT 200 PM EST MONDAY..12Z MODEL RUNS INDICATE THAT SOME SEMBLANCE OF A WEDGE WILL REMAIN THROUGH MOST IF NOT ALL OF TUE NIGHT. THE NAM DOES SUGGEST THAT PERHAPS THE SOUTHERN UPSTATE MAY GET UNCOVERED BY 12Z WED. THE UPSHOT FOR TUE NIGHT IS THAT ISENTROPIC LIFT WILL CONTINUE OVER THE WEDGE WITH WIDESPREAD LIGHT TO EVEN MODERATE RAIN. BEST RAINFALL RATES ARE EXPECTED TO BE OVER THE WESTERN UPSTATE...NE GA MOUNTAINS AND THE WESTERN ESCARPMENT WHERE BEST FORCING/UPSLOPE FLOW WILL BECOME ESTABLISHED. RAINFALL IN THOSE AREAS IS LIKELY TO BE UPWARDS OF AN INCH. ON WED...THE CONSENSUS IS THAT THE REMAINDER OF THE WEDGE WILL GRADUALLY BE UNCOVERED...BUT AS USUAL IT COULD LINGER WELL INTO THE AFTERNOON FROM THE CENTRAL UPSTATE EASTWARD. RAIN/DRIZZLE WILL BECOME SHOWERY AS WEDGE DISSIPATES. THE NEXT ISSUE IS THE COLD FRONT THAT WILL TRANSLATE ACROSS THE AREA FROM THE WEST AS LOW PRESSURE MOVES FROM CENTRAL TN TO THE LOWER GREAT LAKES ON WED. THE 12Z MODELS ARE TRENDING SLOWER WITH THE FRONTAL PASSAGE... WITH THE NAM THE SLOWEST OF THE OPERATIONAL RUNS....A GOOD 6 HOURS SLOWER THAN THE GLOBAL MODELS. THE 09Z SREF SUPPORTS THE SLOWER NAM. IN REGARD TO TIMING WILL USE A CONSENSUS APPROACH WHICH WILL MOVE THE FRONT INTO WESTERN SECTIONS DURING WED AFTERNOON AND THEN ACROSS THE REMAINDER OF THE AREA LATE WED AFTERNOON/EVENING. THE MAIN CONCERN WITH THE FRONTAL PASSAGE WILL BE THE THREAT FOR SOME SORT OF QLCS EVENT. ALL THE MODELS SHOW SOME LOW END CAPE UPWARDS OF 200 J/KG AHEAD OF THE FRONT. SHEAR/HELICITY IS ADEQUATE ALTHOUGH NOT THROUGH THE ROOF BUT FORECAST SHERB VALUES GENERALLY <1. ALSO...THE UPPER FORCING IS NOT COINCIDENT WITH THE FRONT. THE UPPER TROUGH IS FORECAST TO TRAIL THE SURFACE FRONT WITH THE MAIN UPPER FORCING GOING WELL NORTH OF THE REGION. HENCE...CHANCES FOR SEVERE CONVECTION APPEAR ON THE LOW END. THE CIPS ANALOG DOES MAKE ME PAUSE AS IT PAINTS A 30% AREA OF TOP ANALOGS PRODUCING AT LEAST 1 SEVERE EVENT ACROSS THE PIEDMONTS OF NE GA...SC AND NC. SPC KEEPS THE MENTION OF SEVERE EAST OF THE AREA...SO BOTTOM LINE IS THAT WE WILL NOT NOT MENTION THE THREAT OF SEVERE IN THE HWO. DRYER AIR AND DOWNSLOPING WINDS WILL FINALLY SCOUR CLOUDS OUT EAST OF THE MOUNTAINS WED NIGHT WITH PERHAPS A PERIOD OF SOME NW FLOW SNOW/RAIN SHOWERS EARLY CHRISTMAS IN THE MOUNTAINS. IN REGARD TO HYDRO...I HAVE HEFTY QPF IN MY FORECAST GRIDS WITH STORM TOTAL RAINFALL AROUND 2.5 INCHES OVER NE GA...WESTERN UPSTATE AND THE WESTERN ESCARPMENT. HOWEVER...ANTECEDENT CONDITIONS ARE BENIGN SO DO NOT ANTICIPATE ANY SIGNIFICANT HYDRO CONCERNS. TEMPERATURES WILL BE A CHALLENGE AS A NON-DIURNAL TREND WILL OCCUR TUE NIGHT WHERE THE WEDGE ERODES. THIS WOULD MOST LIKELY BE ACROSS THE SOUTHERN PERIPHEREY OF THE FORECAST AREA. TEMPS ON WED SHOULD SURGE WELL INTO THE 60S AS THE WEDGE DISSIPATES. COOLER TEMPS WILL THEN OCCUR WED NIGHT WITH MAX TEMPS THU NEAR CLIMO. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AS OF 200 PM MONDAY...HIGH PRESSURE OVER THE SRN ATLANTIC REGION WILL MAKE FOR SETTLED CONDITIONS IN OUR AREA THU NIGHT THRU EARLY SAT...BEFORE THE HIGH IS FORCED OFFSHORE BY A LONGWAVE TROUGH DIGGING INTO THE CENTRAL CONUS. GLOBAL MODELS HAVE DELAYED ARRIVAL OF THE COLD FRONT ON THE LEADING EDGE OF THE TROUGH...NOW SUGGESTING THE FRONT WILL CROSS THE MTNS DURING THE DAY SAT AT THE EARLIEST. THE GFS HAS MAINTAINED CONSISTENCY WITH EARLIER RUNS...DEAMPLIFYING THE TROUGH OVER THE WEEKEND AND ALLOWING DRY HIGH PRESSURE TO FILL IN ACRS THE SOUTHEAST IN ITS WAKE. EC AND NOW THE OPNL CMC-GEM SHOW A SIMILAR EVOLUTION ALBEIT MARKEDLY DIFFERENT FROM THE GFS. THEY DEPICT A SHORTWAVE SHEARING OFF THE TROUGH OVER THE SRN PLAINS SATURDAY WHICH INDUCES GULF CYCLOGENESIS AND MAKES FOR A WET SUNDAY OVER OUR CWFA. THIS IS NOT INDICATED BY ANY 22/06Z GEFS MEMBERS AND ONLY A COUPLE OF THE 22/12Z GEM ENSEMBLE MEMBERS. NOTING HOW DIFFERENT THE EC/CMC SOLUTION IS FROM EARLIER RUNS IT APPEARS WISE TO DISCOUNT IT TO SOME DEGREE. LOOKING A BIT FURTHER FORWARD...GFS DOES FEATURE ITS OWN DIFFERENCES BY LATE MONDAY AS IT SPINS UP A NEW GULF LOW AT THAT TIME AND BEGINS TO SPREAD PRECIP NWD THRU GA/SC. CONFIDENCE IN THE FCST IS NOT VERY HIGH BEYOND SATURDAY. TEMPS SHOULD TREND UPWARD THRU SUNDAY...WITH MINS ENDING UP A COUPLE DEGREES ABOVE CLIMO AND MAXES 5-7 ABOVE CLIMO. SLIGHTLY COOLER TEMPS RETURN FOR MONDAY WITH HIGH PRESSURE JUST NORTH OF THE REGION. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... DDHHMM WRKTAF AT KCLT...LLVL MOISTURE FEED REMAINS CONSTANT OVER SFC WEDGE WITH DEEPER FORCED MOISTURE MOVING INTO AREA WITHIN THE NEXT FEW HRS. CIGS HOLDING STEADY IN THE IFR/LIFR RANGE AND WILL EXPECT THESE TO PERSIST THROUGHOUT THE TAF PERIOD. INCOMING -RA COULD SCOUR OUT VSBY A BIT INTO THE 3-4SM RANGE...WITH A DROP BACK TO 1SM OR LESS AFT 09Z THRU DAYBREAK. DENSE FG IS POSSIBLE ARND DAYBREAK AS WELL. ANOTHER ROUND OF MODERATE RAIN MOVES IN NEAR THE END OF THE TAF PERIOD WITH VSBYS IMPROVING SOMEWHAT. WINDS REMAIN LOCKED IN NE/LY IN CAD FLOW. ELSEWHERE...SIMILAR CONDS AT ALL SITES THROUGH THE TAF PERIOD. LOW IFR TO LIFR CIGS ALIGNED IN LLVL CAD MOISTURE WILL PERSIST THROUGH THE TAF PERIOD...WHILE -DZ AND -RA AFFECT THE TERMINALS. VSBYS WILL WAVER BACK AND FORTH BETWEEN 1-5SM WITH THE POTENTIAL FOR DENSE FG AROUND DAYBREAK. WINDS REMAIN ALIGNED NE/LY NON/MTNS AND S/LY DOWN VALLEY FLOW AT KAVL. OUTLOOK...DEEP MOISTURE CONTINUES THROUGH TUESDAY NIGHT AHEAD OF THE NEXT APPROACHING COLD FRONT. LOW RESTRICTIONS AND WIDESPREAD RAIN SHOWERS ARE EXPECTED. A COLD FRONT WILL CROSS THE REGION FROM THE WEST ON WED. DRY HIGH PRESSURE WILL RETURN THROUGH LATE WEEK. CONFIDENCE TABLE... 23-05Z 05-11Z 11-17Z 17-18Z KCLT MED 70% MED 75% MED 75% HIGH 80% KGSP MED 70% LOW 58% MED 75% MED 70% KAVL HIGH 80% MED 75% HIGH 91% HIGH 90% KHKY MED 70% MED 75% MED 75% HIGH 90% KGMU MED 70% LOW 58% MED 75% MED 70% KAND MED 70% MED 75% MED 75% MED 70% 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...NONE. SC...NONE. && $$ SYNOPSIS...CSH NEAR TERM...RWH/SBK SHORT TERM...LG LONG TERM...WIMBERLEY AVIATION...SBK

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.