099  
FXUS62 KGSP 270003  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
803 PM EDT SUN MAR 26 2017  
   
SYNOPSIS
 
 
MOIST SOUTHERLY FLOW WILL LINGER OVER THE SOUTHEAST THROUGH TUESDAY,  
WITH SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS POSSIBLE. DRIER AIR  
WILL BRIEFLY RETURN BY THE MIDDLE OF THE WEEK AS A COLD FRONT  
SETTLES SOUTH OF THE AREA. ANOTHER LOW PRESSURE SYSTEM WILL BRING  
MOISTURE BACK TO THE SOUTHEAST THURSDAY, INCREASING RAIN CHANCES  
THROUGH LATE FRIDAY.  
 

 
   
NEAR TERM /THROUGH MONDAY/
 
 
AS OF 750 PM, SHOWER ACTIVITY CONTINUES TO DIMINISH THIS EVENING, A  
TREND THAT SHOULD CONTINUE OVER THE NEXT COUPLE OF HOURS. HOWEVER,  
MESOSCALE MODEL GUIDANCE DEPICTS AN INCREASE IN SHOWER ACTIVITY LATE  
THIS EVENING INTO THE EARLY PART OF THE OVERNIGHT, AS BOUNDARY LAYER  
CONVERGENCE INCREASES NEAR THE ENTRANCE OF A 30-35 KT LLJ.  
THEREFORE, AFTER A DECREASING POP TREND UNTIL LATE EVENING, POPS  
RAMP UP AGAIN TO CHANCE, ESP ACROSS THE EASTERN 2/3 OF THE FORECAST  
AREA THROUGH THE PRE-DAWN HOURS.  
 
OTHERWISE, WE WILL REMAIN IN A MOIST PATTERN WITH SLY LOW-LVL FLOW  
THRU THE NEAR TERM. THE NEXT SFC LOW WILL BE MOVING UP TO OUR NW BY  
THE END OF THE PERIOD 00Z TUES, BRINGING ANOTHER ROUND OF DEEP-LYR  
MOISTURE AND SCT TO WIDESPREAD SHOWERS AND TS TO THE REGION.  
 

 
   
SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/
 
 
AS OF 235 PM EDT SUNDAY: IT LOOKS LIKE THE NEXT IN A SERIES OF UPPER  
TROFS WILL BE ON OUR DOORSTEP MONDAY EVENING, WITH A LEAD VORT MAX  
ALREADY MOVING EASTWARD ACROSS THE REGION AT 00Z TUESDAY. THE MODELS  
ARE A BIT AT ODDS AS TO THE COVERAGE AND PROBABILITY OF PRECIP,  
BUT GENERALLY AGREE THAT WE SHOULD HAVE AT LEAST A CHANCE ACROSS  
THE REGION. WE LOSE THE BETTER LOW LEVEL UPSLOPE FLOW IN ADVANCE OF  
THE WAVE, BUT WE MAKE UP FOR IT WITH MID/UPPER FORCING AS WE WORK  
THRU THE NIGHT. THE UPPER TROF AXIS IS FCST TO CROSS THE REGION  
IN THE 09Z TO 18Z TUESDAY TIME FRAME, WHICH SHOULD LAY A COLD  
FRONT DOWN ACROSS THE REGION DURING THE DAY, AND THEN PUSH IT OFF  
TO THE SOUTH BY THE END OF THE DAY. THIS OUGHT TO GIVE US ANOTHER  
NON-ZERO CHANCE OF STRONG TO SEVERE THUNDERSTORMS, BUT THIS SET-UP  
WILL HAVE MORE OF THE SAME PROBLEMS AS RECENT DAYS, THAT BEING POOR  
LAPSE RATES AND A TALL THIN CAPE PROFILE. SHEAR WILL ALSO NOT BE  
QUITE AS GOOD, BUT WE MIGHT HAVE MORE OF A TRIGGER. HAVE TO THINK  
RIGHT NOW OUR CHANCES ARE LOW. PRECIP PROB SHOULD DIMINISH IN THE  
AFTERNOON AS DOWNSLOPE FLOW DEVELOPS EAST OF THE BLUE RIDGE. WE END  
THE DAY WITH LINGERING W/NW FLOW UPSLOPE SHOWERS ON THE TN BORDER,  
BUT THAT TOO SHOULD DIE OFF TUESDAY NIGHT.  
 
WEDNESDAY LOOKS FAIRLY BENIGN, YET SOMEWHAT PROBLEMATIC. THERE ARE  
INDICATIONS THAT A REINFORCING BACK-DOOR COLD FRONT WILL PUSH DOWN  
FROM THE N/NE IN THE AFTERNOON, WHICH COULD HAVE AN AFFECT ON THE  
HIGH TEMP FCST, ESPECIALLY OVER THE NW PIEDMONT. HAVE STUCK CLOSE  
TO THE RAW BLEND OF THE GUIDANCE FOR NOW, BUT THIS COULD EASILY  
HAVE TO BE LOWERED A FEW CATEGORIES IF THE BACK DOOR ARRIVES EARLY.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
 
 
AS OF 200 PM EDT SUNDAY: THE MEDIUM RANGE FCST PERIOD INITIALIZES  
ON WEDNESDAY EVENING AMIDST AN UPPER RIDGE AXIS ATOP THE EASTERN  
CONUS, WHILE A RATHER ROBUST CLOSED H5 CYCLONE DEEPENS ACROSS THE  
SOUTHERN PLAINS. AS A RESULT OF THE HIGHLY AMPLIFIED PATTERN ALOFT,  
THE SURFACE FIELD WILL ALSO BE RATHER INTERESTING AS CYCLOGENESIS  
BENEATH THE AFOREMENTIONED UPPER CYCLONE LIFTS A WARM FRONT ACROSS  
THE DEEP SOUTH SETTING UP AN INCREASINGLY LARGE BAROCLINIC  
ZONE. IN ADDITION TO THAT, HIGH PRESSURE OVER THE GREAT LAKES  
WILL SLIDE EAST BEFORE EXTENDING SOUTHWARD IN THE LEE OF THE  
APPALACHIANS SETTING UP CAD.  
 
PATTERN EVOLUTION THROUGH THE PERIOD WILL BE HIGHLIGHTED BY THE  
INTERACTIONS OF THE ABOVE MENTIONED FEATURES THURSDAY/FRIDAY  
AS THE MS VALLEY CENTERED UPPER SYSTEM ADVECTS EAST, INTO THE  
DESTABILIZED WARM SECTOR OVER DIXIE ALLEY POSSIBLY LEADING TO  
WIDESPREAD STRONG/SEVERE CONVECTION ON THURSDAY. AT THE SAME TIME  
WARM/MOIST GOM AIR WILL SPREAD NORTHWARD ALONG A WARM FRONT INTO  
NORTH GA AND THE WESTERN CAROLINAS, WITH SAID MOISTURE LIFTING  
ISENTROPICALLY TO YIELD ISO/SCT RA ATOP THE WESTERN PERIPHERY OF  
THE RIDGE THURSDAY NIGHT INTO FRIDAY MORNING. BY THAT TIME THE  
ENTIRE CONVECTIVE COMPLEX WILL HAVE SHIFTED EAST INTO THE OH/TN  
VALLEYS AS THE ASSOCIATED COLD FRONT LOOKS TO CROSS THE MS RIVER.  
AT THAT POINT THE DETAILS BECOME A BIT UNCLEAR AS TO HOW THE  
APPROACHING WAVE WILL INTERACT WITH THE STUBBORN CAD WEDGE GIVEN  
THAT THE OP MODELS FEATURE SOME DISCONTINUITIES. SPECIFICALLY THE  
GFS IS A BIT MORE PROGRESSIVE HOWEVER LESS AMPLIFIED OVERALL,  
WHILE THE ECMWF IS SLOWER, WHICH IF PERFECT PROGGED WOULD LEAD TO  
BETTER CHANCES FOR WIDESPREAD STRONG/SEVERE CONVECTION ON FRIDAY  
GIVEN IMPRESSIVE SHEAR AND IMPROVING LAPSE RATES THANKS TO THE  
APPROACHING NEGATIVELY TILTED H5 TROF AXIS. THE FASTER AND LESS  
AMPLIFIED GFS LOOKS RELATIVELY UNSTABLE AT THIS RANGE, HOWEVER  
THE FLOW IS FCST TO BE MORE VEERED OVERALL AS THE UPPER WAVE HAS  
PASSED AND ANY CAD TMB HAS RETREATED FURTHER NORTH. ALL SAID, THESE  
DETAILS WILL LIKELY MODIFY WITH TIME GIVEN ADDITIONAL GUIDANCE AND  
NARROWING OF SCOPE. BEYOND THAT, THE COLD FRONT WILL SWEEP ACROSS  
THE FCST ARE ON FRIDAY NIGHT INTO SATURDAY AS DEEP RIDGING BUILDS  
TO THE WEST. GUIDANCE DOES HINT AT SOME REMNANT UPSLOPE SHOWERS  
BEHIND THE FRONT ON SATURDAY MORNING, EVENTUALLY DRYING INTO THE  
AFTERNOON HOURS. SAID RIDGING WILL DOMINATE ON SUNDAY BEFORE  
ANOTHER DEEPENING PLAINS SYSTEM APPROACHES TO ROUND OUT THE PERIOD.  
 
AS FOR THE FCST, POPS WILL RAMP UP ACROSS THE CWFA ON THURSDAY AS  
THE WEDGE SETTLES ATOP THE PIEDMONT/FTHILLS THUS PROVIDING ENHANCED  
FOCUS FOR UPGLIDE RA, THEN INCREASING/SPREADING ATOP THE ENTIRE  
REGION TO FEATURE HIGH END CHANCES TO LOW END LIKELY LEVELS INTO  
FRIDAY MORNING. POPS WILL HOLD AT THESE LEVELS THROUGH MUCH OF  
THE DAY FRIDAY BEFORE TAPERING OVERNIGHT, EVENTUALLY LEADING TO  
SLIGHT CHANCES NORTH OF I85 BY DAYBREAK SATURDAY. BEYOND THAT,  
MENTIONABLE POPS WILL RETREAT TO THE CENTRAL/NORTHERN MTNS  
SATURDAY AFTERNOON BEFORE DRYING OUT COMPLETELY SATURDAY NIGHT,  
LASTING THROUGH PERIODS END. TEMPERATURES WILL BE A BIT TRICKY  
EARLY IN THE PERIOD AS THE WEDGE AND ASSOCIATED UPGLIDE STRATIFORM  
PRECIPITATION WORK TO KEEP HIGHS BELOW NORMAL ON THURSDAY, BEFORE  
WARMING BACK TO NEAR NORMAL LEVELS TO ROUND OUT THE PERIOD.  
 

 
   
AVIATION /00Z MONDAY THROUGH FRIDAY/
 
 
AT KCLT: SHOWERS ARE DISSIPATING NEAR THE TERMINAL THIS EVENING, BUT  
WITH ADDITIONAL ACTIVITY ABOUT 40 MILES UPSTREAM, DECIDED TO LEAVE  
THE VCSH GOING TO START THE PERIOD. MEANWHILE, HIGH RESOLUTION  
GUIDANCE SUGGESTS AFTER AN INITIAL MID/LATE EVENING LULL, SHOWER  
ACTIVITY MAY INCREASE AGAIN AROUND MIDNIGHT, SO ALLOWED THE VCSH TO  
PERSIST THROUGH MUCH OF THE NIGHT. PLENTY OF LOW LEVEL MOISTURE WILL  
LINGER ACROSS THE AREA THROUGH THE OVERNIGHT, SO CIG AND VISBY  
RESTRICTIONS ARE IN PLAY, BUT CONFIDENCE IS PRETTY LOW AS TO HOW  
POOR CONDITIONS WILL BECOME. CATEGORICAL MVFR CONDITIONS ARE  
INTRODUCED AT AROUND 08Z, WITH TEMPO FOR 3SM/FEW003 BKN015 BTW 10  
AND 12Z. WIDELY SCATTERED SHOWERS ARE EXPECTED TO DEVELOP ACROSS THE  
AREA MONDAY AFTERNOON, AND A VCSH IS INCLUDED THROUGHOUT THE  
AFTERNOON.  
 
ELSEWHERE: OVERALL SIMILAR TRENDS TO KCLT, ALTHOUGH CHANCES FOR  
RESTRICTIONS APPEAR MUCH HIGHER AT KAVL AND ESPECIALLY KHKY, WHERE  
TEMP/DEWPOINT SPREADS WERE ALREADY LESS THAN 5 DEGREES AT FORECAST  
TIME. THEREFORE, INTRODUCE TEMPOS FOR MVFR AT KHKY BY MIDNIGHT, WITH  
CATEGORICAL IFR CONDITIONS FORECAST DURING THE PRE-DAWN HOURS.  
SIMILAR CONDITIONS AT KAVL, ALBEIT A BIT LATER.  
 
OUTLOOK: MOIST PATTERN WITH SLY LOW-LVL FLOW WILL PERSIST, WITH  
ANOTHER FRONTAL SYSTEM IMPACTING THE AREA LATE MONDAY INTO TUESDAY.  
THIS SYSTEM WILL LIKELY CREATE ADDITIONAL FLIGHT RESTRICTIONS ACROSS  
THE REGION. FAIR CONDITIONS SHOULD BRIEFLY RETURN DURING MID-WEEK  
BEFORE ANOTHER STORM SYSTEM BEGINS AFFECTING THE REGION THURSDAY AND  
FRIDAY.  
 
CONFIDENCE TABLE...  
 
00-06Z 06-12Z 12-18Z 18-00Z  
KCLT HIGH 100% HIGH 89% HIGH 83% HIGH 98%  
KGSP HIGH 100% MED 76% HIGH 85% HIGH 100%  
KAVL MED 74% MED 68% MED 71% HIGH 100%  
KHKY HIGH 93% MED 69% HIGH 82% HIGH 94%  
KGMU HIGH 100% MED 78% HIGH 86% HIGH 100%  
KAND HIGH 100% HIGH 84% MED 78% HIGH 96%  
 
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:  
 
WWW.WEATHER.GOV/GSP/AVIATION  
 

 
   
GSP WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
NC...NONE.  
SC...NONE.  
 

 
 

 
SYNOPSIS...LEV  
NEAR TERM...JDL/JPT  
SHORT TERM...PM  
LONG TERM...CDG  
AVIATION...JDL  
 
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