530  
FXUS62 KGSP 261047  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
647 AM EDT WED APR 26 2017  
   
SYNOPSIS
 
 
WARM AND DRY HIGH PRESSURE WILL BUILD IN ACROSS THE REGION TODAY. A  
DISSIPATING COLD FRONT CROSSES OUR REGION THURSDAY, THEN WARM AND  
HUMID HIGH PRESSURE BUILDS BACK IN FOR FRIDAY AND SATURDAY. ANOTHER  
FRONT APPROACHES FROM THE WEST ON SUNDAY.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 645 AM EDT: LOW CLOUDS LINGER OVER THE I-40 CORRIDOR WITH FOG  
SPREADING OUT ACROSS THE FOOTHILLS INTO THE NORTHERN UPSTATE THIS  
MORNING. MOUNTAIN VALLEY FOG HAS DEVELOPED AS WELL. THE FOG WILL BE  
PATCHY DENSE, SO ISSUED AN SPS FOR THE POTENTIAL TRAVEL PROBLEMS.  
THE FOG SHOULD DISSIPATE BY 14Z WITH THE LOW CLOUDS OVER THE I-40  
CORRIDOR POSSIBLY LINGERING THROUGH NOON.  
 
SOUTHERLY FLOW DEVELOPS BETWEEN A DEPARTING HIGH PRESSURE CENTER AND  
A COLD FRONT MOVING INTO THE MS RIVER VALLEY. LOTS OF SUNSHINE AND  
INCREASING THICKNESS VALUES AS A RIDGE MOVES OVERHEAD WILL LEAD TO  
HIGHS IN THE 80S ACROSS MUCH OF THE AREA.  
 
THE RIDGE AXIS MOVES EAST TONIGHT AND A SHORT WAVE APPROACHES FROM  
THE WEST. THIS WAVE PUSHES THE COLD FRONT INTO MIDDLE TN AND AL  
OVERNIGHT. THE CONTINUED MOIST SOUTHERLY FLOW WILL LEAD TO AN  
INCREASE IN CLOUDS OVERNIGHT. ISOLATED SHOWERS MAY DEVELOP ACROSS  
THE NE GA MOUNTAINS AND THE FAR SW NC MOUNTAINS BY DAYBREAK, BUT THE  
REST OF THE AREA WILL REMAIN DRY. LOWS WILL BE AROUND 10 DEGREES  
ABOVE NORMAL.  
 

 
   
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
 
 
AS OF 315 AM EDT WEDNESDAY: A NEGATIVELY TILTED SHORT WAVE TROUGH  
WILL LIFT NE ACROSS THE OHIO VALLEY ON THURSDAY, BRUSHING THE NC  
MOUNTAINS EARLY IN THE DAY. AN ASSOCIATED COLD FRONT WILL BRING A  
LINE OF DECAYING CONVECTION, WHICH SHOULD MOVE INTO THE WESTERN HALF  
OF THE CWFA IN THE 12-18Z TIME FRAME. THIS MAY LEAVE PLENTY OF CLOUD  
COVER WHICH MAY LIMIT INSTABILITY FOR THE AFTERNOON. BUT MODELS DO  
SHOW ENOUGH FORCING TO KEEP THE CONVECTION GOING (ALBEIT IN PROBABLY  
WEAK FORM) INTO THE EASTERN HALF OF THE CWFA. THE NEW DAY 2  
CONVECTIVE OUTLOOK FROM SPC STILL HAS A LARGE MARGINAL RISK FROM THE  
GREAT LAKES TO THE FL GULF COAST, NUDGED A LITTLE EAST FROM THE OLD  
DAY 3 OUTLOOK. TEMPS WILL BE BE A LITTLE COOLER THAN TODAY'S  
READINGS UNDER THE CLOUDS AND PRECIP, BUT STILL ABOVE NORMAL.  
 
THURSDAY NIGHT THRU FRIDAY NIGHT, THE FRONT WILL WASH OUT AND LEAVE  
A WARM HUMID AIR MASS IN PLACE. FORECAST SOUNDINGS ON FRIDAY SHOW A  
"LOADED GUN" TYPE SOUNDING, WITH A SIGNIFICANT CAP ABOVE THE TOP OF  
THE MIXED LAYER. GUIDANCE HAS TRENDED LESS CONVECTIVE, SO POPS WERE  
REDUCED TO JUST SLIGHT CHC, MAINLY IN THE MOUNTAINS WHERE TERRAIN  
EFFECTS MAY BE ENOUGH TO POP A FEW STORMS. THOSE THAT DO DEVELOP (IF  
WE DO GET THE 2500 J/KG ADVERTISED IN BOTH NAM AND GFS) MAY BE QUITE  
STRONG. SHEAR ALSO REMAINS HIGH ENOUGH FOR QUASI-ORGANIZED CELLS,  
BUT THE LIMITED UPPER FORCING AND THE STRONG CAP SHOULD LIMIT  
COVERAGE. HIGHS REBOUND BACK INTO THE LOWER TO MID 80S ACROSS THE  
PIEDMONT. LOWS ABOUT 10-15 DEGREES ABOVE NORMAL.  
 

 
   
LONG TERM /SATURDAY THROUGH TUESDAY/
 
 
AS OF 330 AM EDT WEDNESDAY: A HIGH AMPLITUDE UPPER RIDGE WILL BUILD  
ALONG THE EAST COAST, WHILE A BERMUDA HIGH PATTERN SETS UP OVER THE  
SOUTHEAST. THIS WILL BRING SUMMER-LIKE CONDITIONS FOR SATURDAY INTO  
SUNDAY, WITH TEMPS SATURDAY APPROACHING 90 IN PORTIONS OF THE  
PIEDMONT. PERSISTENT LOW-LEVEL SOUTHERLY FLOW WILL BRING MORE  
MOISTURE IN, AND IT LOOKS LIKE WE WILL BE LESS CAPPED THAN FRIDAY.  
SO POPS WILL FEATURE SLIGHTLY BETTER COVERAGE, BUT STILL ISOLATED TO  
WIDELY SCATTERED IN NATURE. THE GFS ADVERTISES ANOTHER DAY OF  
1500-2500 J/KG OF SBCAPE, WHILE THE ECMWF AND CANADIAN SHOW MORE  
LIKE 1000-1500 J/KG. ALSO, SHEAR AND UPPER SUPPORT WILL BE WEAKER  
FOR CONVECTION. SO PULSE STORM MODE IS MOST LIKELY AND SEVERE THREAT  
SHOULD BE LOW.  
 
SUNDAY AND MONDAY, THE BROAD UPPER TROUGH OVER THE WESTERN CONUS  
WILL SHARPEN AND CLOSE OFF AN UPPER LOW OVER THE MIDWEST, THEN LIFT  
INTO THE GREAT LAKES. THIS WILL BRING ANOTHER NEGATIVELY TILTED  
TROUGH ACROSS THE AREA ON MONDAY. THE MEDIUM RANGE GUIDANCE IS IN  
DECENT AGREEMENT ON THIS, AND ALSO ON THE TIMING OF THE ASSOCIATED  
COLD FRONT EARLY MONDAY. THIS FRONT LOOKS TO BE STRONGER AND MORE  
STRONGLY FORCED THAN THE THURSDAY FRONT, BUT CURRENTLY LOOKS TO  
CROSS DURING THE DIURNAL MINIMUM FOR INSTABILITY. SO WHILE  
CONFIDENCE IN POPS GOES UP, AS FAR AS SEVERE THREAT, CONFIDENCE  
REMAINS LOW. TEMPS WILL ALSO BE TRICKY, AS THE GFS IN PARTICULAR,  
SHOWS PLENTY OF SOUTHERLY UPSLOPE CLOUDS AND PRECIP DEVELOPING ON  
SUNDAY, WHILE THE ECMWF IS DRIER. IF THE GFS IS RIGHT, TEMPS SHOULD  
BE AT LEAST A COUPLE CATEGORIES COOLER THAN SATURDAY. HOWEVER, IF  
THE EC IS RIGHT, SUNDAY COULD BE ANOTHER HOT DAY FOR LATE APRIL. I  
OPTED TO BLEND IN SOME OF THE EC TEMPS FOR SUNDAY, GOING SLIGHTLY  
ABOVE THE SUPERBLEND. TEMPS SHOULD BE NEAR OR SLIGHTLY BELOW NORMAL  
BEHIND THE FRONT MONDAY AND TUESDAY.  
 

 
   
AVIATION /12Z WEDNESDAY THROUGH SUNDAY/
 
 
AT KCLT AND ELSEWHERE: CLT LOOKS TO STAY VFR THIS MORNING WITH LOW  
CLOUDS AND FOG REMAINING NORTH AND WEST OF THE AIR FIELD. ELSEWHERE,  
LOW CLOUDS AND FOG THIS MORNING WILL DISSIPATE BY 14Z LEAVING CIRRUS  
IN PLACE. WINDS GO S TO SW ALL AREAS THROUGH THE AFTERNOON AND  
REMAIN THERE OVERNIGHT, ALTHOUGH WITH DIMINISHING SPEEDS. CIRRUS  
INCREASES THROUGH THE EVENING WITH LOWER VFR MOVING IN FROM THE  
WEST AHEAD OF A COLD FRONT BY DAYBREAK. EXPECT ANY RESTRICTIONS AND  
PRECIP TO REMAIN WEST OF THE AREA THROUGH DAYBREAK AS WELL.  
 
OUTLOOK: RETURN FLOW MOISTURE INCREASES AHEAD OF THE NEXT SYSTEM  
THURSDAY INTO FRIDAY WITH THE POTENTIAL FOR THUNDERSTORMS  
INCREASING. SCATTERED, DIURNAL THUNDERSTORMS WILL THEN CONTINUE OVER  
THE WEEKEND.  
 
CONFIDENCE TABLE...  
 
10-16Z 16-22Z 22-04Z 04-06Z  
KCLT HIGH 83% HIGH 100% HIGH 100% HIGH 100%  
KGSP HIGH 94% HIGH 100% HIGH 100% HIGH 100%  
KAVL HIGH 89% HIGH 100% HIGH 100% HIGH 100%  
KHKY HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KGMU HIGH 97% HIGH 100% HIGH 100% HIGH 100%  
KAND HIGH 94% 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:  
 
WWW.WEATHER.GOV/GSP/AVIATION  
 

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

 
 

 
SYNOPSIS...ARK  
NEAR TERM...RWH  
SHORT TERM...ARK  
LONG TERM...ARK  
AVIATION...RWH  
 
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