264  
FXUS62 KGSP 260603  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
203 AM EDT WED JUL 26 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE MOVING BY TO THE NORTH IS EXPECTED TO PROVIDE COOLER  
TEMPERATURES ON WEDNESDAY. ANOTHER FRONT WILL MOVE IN FROM THE  
NORTHWEST LATE IN THE WEEK, WITH COOLER AND DRIER CONDITIONS  
ARRIVING BEHIND IT FOR THE WEEKEND.  
 

 
   
NEAR TERM /THROUGH TODAY/
 
 
AS OF 200 PM EDT WEDNESDAY: THE ROGUE TSTM OVER OCONEE COUNTY HAS  
DISSIPATED, AND ANY ADDITIONAL CONVECTION IS EXPECTED TO BE MAINLY  
JUST LIGHT SHOWERS. THE CAMS GENERALLY AGREE ON A FEW SHOWERS  
BUBBLING WITHIN A MOIST, ALBEIT WEAK, EASTERLY UPSLOPE FLOW IN THE  
NC FOOTHILLS THRU DAYBREAK. SO WILL ADD A LOW-END CHC POP THERE  
USING CAMPOP. SKY COVER WAS ADJUSTED WITH LATEST GUIDANCE. STILL  
LOOKS LIKE MOISTURE ADVECTING FROM THE EAST WILL SUPPORT STRATUS  
DEVELOPMENT INTO THE NC PIEDMONT. TEMPS LOOK ON TRACK.  
 
THE PATTERN OF EVENTS ON WEDNESDAY MAY BE FAIRLY SIMILAR TO TODAY,  
WITH SOME WIDELY SCATTERED AFTERNOON SHOWERS, WITH SOME CHANCE FOR  
STRONG TO SEVERE STORMS. INSTABILITY MAY CREEP UP A LITTLE BIT AS  
BETTER DEWPOINTS ADVANCE NORTHWESTWARD. GENERAL SYNOPTIC PATTERN IS  
NEARLY IDENTICAL ON WEDNESDAY WITH ZONAL 591 500MB HEIGHT LINE  
HARDLY MOVING, AND NEGLIGIBLE SURFACE FEATURES. LACK OF SURFACE  
FEATURES AND ANY UPPER LEVEL SUPPORT WILL CAUSE THE PATTERN OF  
INITIATION OVER HIGHER TERRAIN TO CONTINUE.  
 

 
   
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/
 
 
AS OF 200 PM EDT TUESDAY: UPPER-LEVEL HEIGHTS WILL BEGIN FALLING  
FROM THE GREAT LAKES TO THE OHIO RIVER VALLEY WEDNESDAY NIGHT  
THROUGH THURSDAY. AT LOW LEVELS, LIGHT SOUTHERLY UPSLOPE FLOW COULD  
PERMIT ISOLATED TO SCATTERED SHOWERS, WITH A THUNDERSTORM OR TWO, TO  
PERSIST INTO THE NIGHTTTIME HOURS EARLY THURSDAY ACROSS THE SOUTHERN  
MOUNTAINS. OTHERWISE, ANTICIPATE SLIGHTLY BETTER DIURNAL CONVECTIVE  
COVERAGE ACROSS THE NC MOUNTAINS THURSDAY AFTERNOON AND EVENING  
AHEAD OF THE APPROACHING UPPER SUPPORT AS SURFACE-BASED INSTABILITY  
INCREASES A BIT OVER PREVIOUS DAYS. IMPROVING WESTERLY STEERING FLOW  
WILL ALSO LIKELY BRING SCATTERED CONVECTION FARTHER EAST OF THE BLUE  
RIDGE ALONG THE I-40 CORRDOR INTO THE WESTERN NC FOOTHILLS/PIEDMONT  
INTO THURSDAY EVENING. SURFACE TO 6 KM BULK SHEAR MAGNITUDE MAY RISE  
TO 25 TO 30 KT ACROSS THE NORTHERN TIER BY THURSDAY AFTERNOON AS  
THESE WESTERLIES IMPROVE. THUS, ANTICIPATE A GRADUAL CHANGE IN THE  
CHARACTER OF THE CONVECTION TO MORE MULTI-CELL TYPES BY LATE  
THURSDAY.  
 
THE UPSTREAM SHORTWAVE ENERGY WILL CROSS THE FORECAST AREA FROM THE  
NORTHWEST THURSDAY NIGHT THROUGH FRIDAY AHEAD OF MUCH STRONGER  
HEIGHTS FALLS CARVING OUT A MORE PROMINENT TROUGH FROM THE GREAT  
LAKES TO THE APPALACHIANS. THE BEST MOISTURE AND FORCING WILL OCCUR  
AROUND THE PASSING COLD FRONT, BUT THE NUMERICAL MODELS STILL  
EXHIBIT QUITE A BIT OF SPREAD ON THE TIMING. THE FASTER NAM/ECM  
CAMPS BRING CLOUDS AND MOISTURE INTO THE REGION VERY EARLY FRIDAY  
AND THUS LIMIT INSTABILITY, WHILE THE GFS TIMING IS MUCH LATER IN  
THE DAY. INDEED, THE SLOWER GFS WOULD KEEP PRECIPITATION GOING WELL  
INTO FRIDAY NIGHT ACROSS THE SOUTHEAST HALF OF THE AREA. THIS WILL  
PLAY HAVOC WILL INSTABILITY AROUND THE FROPA AND ALSO SHEAR  
PROFILES, BUT AN UPTICK IN STORM ORGANIZATION IS CERTAINLY POSSIBLE  
FRIDAY AFTERNOON AND EVENING. FOR NOW, WILL BLEND THE TIMING  
SLIGHTLY TOWARD THE FASTER SOLUTIONS WHICH IS PREFERRED GIVEN THE  
PUSH FROM THE RAPIDLY FALLING UPSTREAM HEIGHTS.  
 

 
   
LONG TERM /SATURDAY THROUGH TUESDAY/
 
 
AS OF 200 PM EDT TUESDAY: A TREND TOWARD DRIER AND COOLER CONDITIONS  
SEEN IN THE PREVIOUS FORECAST WAS CONTINUED WITH THIS FORECAST  
PACKAGE. BY SATURDAY MORNING, A SURFACE COLD FRONT SHOULD HAVE MOVED  
THROUGH OUR AREA AND SETTLED TO OUR SOUTH. THE GFS/ECMWF REMAIN IN  
AGREEMENT ON MAINTAINING AN AMPLIFIED PATTERN AND SWEEPING THIS  
FRONT THROUGH TOWARDS THE GULF COAST, WITH AN UPPER LONGWAVE TROUGH  
DEEPENING OVER THE EASTERN CONUS OVER THE WEEKEND AND INTO EARLY  
NEXT WEEK. THERE IS ALSO BETTER AGREEMENT IN THE GLOBAL MODELS WITH  
RESPECT TO DRIER AIR ARRIVING BEHIND THE FRONT...AND WITH BASICALLY  
ALL CONVECTION REMAINING SUPPRESSED SATURDAY AND SUNDAY OVER OUR  
AREA IN YET ANOTHER GUIDANCE CYCLE, HAVE LOWERED POPS EVEN MORE TO  
BELOW CLIMO OVER THE WEEKEND. THE BERMUDA HIGH REASSERTS ITSELF A  
BIT MORE OVER THE SOUTHEAST EARLY NEXT WEEK, AND GRADUAL MOISTENING  
OF THE COLUMN WILL LEAD TO POPS RETURNING CLOSER TO AVERAGE BY  
TUESDAY AND WEDNESDAY.  
 
WITH THE ABOVE-MENTIONED UPPER TROUGH EXPECTED TO DEEPEN  
DRAMATICALLY OVER THE EASTERN CONUS OVER THE WEEKEND AND INTO EARLY  
NEXT WEEK, MAINTAINED THE DOWNWARD TREND IN TEMPERATURES THROUGH THE  
PERIOD. LARGE ADJUSTMENTS WEREN'T MADE WITH THIS PACKAGE, BUT  
TEMPERATURES MORE THAN 5 DEGREES BELOW CLIMO AND DEW POINTS IN THE  
MID TO LOW 60S COULD MAKE FOR SOME...DARE I SAY IT...RATHER PLEASANT  
CONDITIONS FOR LATE JULY.  
 

 
   
AVIATION /06Z WEDNESDAY THROUGH SUNDAY/
 
 
AT KCLT AND ELSEWHERE: EASTERLY LOW-LEVEL FLOW IS SETTING UP ATOP  
THE AREA DURING THE PRE-DAWN HOURS, AND WILL HELP SUPPORT MVFR TO  
POSSIBLY SOME IFR STRATUS DEVELOPMENT ACROSS MAINLY THE NC PIEDMONT  
SITES THRU DAYBREAK. WITH UPSLOPE FLOW, THO WEAK, MAY SUPPORT  
ONGOING -SHRA NEAR KHKY, SO WILL ADD VCSH FOR THE NEXT FEW HOURS.  
GUIDANCE GENERALLY DOESN'T DEVELOP STRATUS WEST ENOUGH TO AFFECT THE  
UPSTATE SITES. AT KAVL, VALLEY FOG AND STRATUS IS EXPECTED TO  
DEVELOP. AFTER SUNRISE, LOW CLOUDS WILL BE SLOW TO LIFT AND SCATTER  
OUT DUE TO THE MOIST EASTERLY FLOW, BUT SHOULD GO TO VFR BY MIDDAY  
AT ALL SITES. SLIGHTLY BETTER COVERAGE OF AFTERNOON CONVECTION IS  
EXPECTED ACROSS THE AREA. SO PROB30 FOR TSRA WILL BE CARRIED IN ALL  
THE TAFS. WINDS WILL BE LIGHT THRU THE PERIOD, FAVORING A NE  
DIRECTION THRU MIDDAY, THEN SE THIS AFTERNOON AND EVENING.  
 
OUTLOOK: SCATTERED DIURNAL CONVECTION CAN BE EXPECTED EACH DAY  
THRU FRIDAY ACROSS THE REGION. THEN DRIER AIR WILL FILTER IN FROM  
THE NORTH BEHIND A PASSING COLD FRONT THIS WEEKEND. CHANCES FOR  
MORNING FOG AND STRATUS WILL ALSO BE POSSIBLE EACH DAY IN THE  
MOUNTAIN VALLEYS.  
 
CONFIDENCE TABLE...  
 
06-12Z 12-18Z 18-24Z 00-06Z  
KCLT HIGH 94% HIGH 83% HIGH 99% HIGH 100%  
KGSP HIGH 91% HIGH 100% HIGH 100% HIGH 100%  
KAVL MED 75% HIGH 89% HIGH 100% HIGH 96%  
KHKY HIGH 96% MED 79% HIGH 94% HIGH 100%  
KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KAND HIGH 91% HIGH 94% 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...CARROLL  
NEAR TERM...ARK/WJM  
SHORT TERM...HG  
LONG TERM...CARROLL  
AVIATION...ARK  
 
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