917  
FXUS62 KGSP 251913  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
313 PM EDT FRI MAY 25 2018  
   
SYNOPSIS
 
 
UNSETTLED WEATHER WILL PERSIST OVER THE NEXT WEEK AS WE REMAIN  
UNDER A WARM AND HUMID AIR MASS. AS LOW PRESSURE DEVELOPS OVER  
THE GULF OF MEXICO, DEEP TROPICAL MOISTURE WILL THEN OVERSPREAD  
THE AREA THE LATTER HALF OF THE WEEKEND AND PERSIST INTO NEXT  
WEEK, BRINGING POTENTIALLY HEAVY RAINFALL FOR THE MEMORIAL DAY  
WEEKEND AND THROUGH THE MIDDLE PART OF NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH SATURDAY/
 
 
AS OF 2:30PM EDT FRIDAY: FAIRLY TROPICAL CONDITIONS CONTINUE WITH A  
WEAK SHORTWAVE EMBEDDED IN THE UPPER FLOW THAT HAS MOST OF ITS  
ENERGY WELL NORTH, BUT ENOUGH BITS OF VORTICITY OVER THE GSP AREA TO  
ENHANCE PRECIPITATION TODAY. CURRENTLY THERE ARE FAIRLY WIDE SPREAD  
SHOWERS AROUND THE REGION, AND MOST PLACES WILL RECEIVE SOME RAIN  
TODAY. AREA OF SHOWERS IS MOVING NORTHWARD FROM THE PIEDMONT INTO  
THE MOUNTAINS. UPSLOPE ENHANCEMENT IN THE FOOTHILLS WILL GIVE SOME  
HEAVIER RAINFALL AMOUNTS IN THAT AREA. RAINFALL TOTALS FOR TODAY AND  
TOMORROW WILL RANGE FROM A QUARTER INCH TO AN INCH, WITH SOME  
ISOLATED AREAS UP TO 2 INCHES THAT RECEIVE REPEATED HEAVY SHOWERS.  
THUNDERSTORMS WILL BECOME MORE LIKELY AS THE AFTERNOON PROGRESSES,  
AND DECLINE AFTER DARK. SOME RAIN CHANCES CONTINUE THROUGH THE NIGHT  
WITH A MINIMUM IN POP AROUND 8AM SATURDAY. SHOWERS AND THUNDERSTORMS  
ARE AGAIN EXPECTED ON SATURDAY, MORE NUMEROUS IN THE AFTERNOON, BUT  
NOT AS WIDESPREAD AS FRIDAY AS WEAK FORCING FROM UPPER WAVE MOVES  
NORTHEASTWARD.  
 
ABUNDANT MOISTURE WITH DEWPOINTS IN THE MID TO UPPER 60S WILL  
CONTINUE AND GIVE GENERALLY CLOUDY CONDITIONS WITH A NARROW DIURNAL  
TEMPERATURE RANGE WITH LOWS 5 TO 10 DEGREES ABOVE NORMAL AND HIGHS  
NEAR NORMAL. IN THE ABSENCE OF ANY STRONG LOW-LEVEL FEATURES, WINDS  
WILL ALSO CONTINUE FAIRLY LIGHT AND SOUTHERLY WITH OCCASIONAL GUSTY  
CONDITIONS FROM STORM OUTFLOWS.  
 

 
   
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
 
 
AS OF 230 PM EDT FRIDAY: THE MODELS ARE STILL SUGGESTING A LULL  
DEVELOPING SATURDAY NIGHT, AS THE DIURNAL CONVECTION FADES. BUT  
CONSIDERING THE TROPICAL NATURE OF THE AIRMASS WE WILL RAMP ALL,  
EXCEPT THE NC MOUNTAINS, INTO THE CHANCE CATEGORY. THIS FITS THE  
MODEL MODE OF REDEVELOPING THE WESTERN ATLANTIC RIDGE, WEST INTO  
OUR FORECAST AREA (FA).  
 
MEANWHILE, THE PUSH OF DEEPER TROPICAL MOISTURE WILL BE MAKING A  
MOVE TO THE NORTH SUNDAY, ON THE EASTERN FLANK OF SUBTROPICAL STORM  
ALBERTO. IT APPEARS THAT SCATTERED TO NUMEROUS SHOWERS AND  
THUNDERSTORMS WILL DEVELOP IN A DIURNAL TYPE FASHION, WITH A SLUG OF  
INSTABILITY ADDING FUEL TO THE FIRE. WITH PRECIPITABLE WATER VALUES  
(PW'S) FLIRTING WITH THE 90TH PERCENTILE, LOCALLY HEAVY RAIN WILL BE  
POSSIBLE.  
 
THE MOISTURE FROM THE OUTER BAND OF SUBTROPICAL STORM ALBERTO WILL  
OVERSPREAD OUR FA SUNDAY NIGHT AND MONDAY. PW'S RUN TO 1.5 TO OVER  
2.0 INCHES. WE WOULD EXPECT POTENTIAL HEAVY RAIN TO START LATE ON  
SUNDAY NIGHT INTO MONDAY. NOTE MODEL DIFFERENCES ARE STILL IN PLAY  
CONCERNING TIMING AND AMOUNTS. HOWEVER NO MATTER HOW YOU SLICE IT,  
THE HIGH PW'S NEED TO BE WATCHED CAREFULLY FOR EXCESSIVE RAINFALL  
AND ALSO A POTENTIAL PREDECESSOR EVENT.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
 
 
AS OF 230 PM FRIDAY...AFTER WE GET PAST MONDAY, WE TURN OUR ATTENTION  
TOWARD THE EVENTUAL FATE OF WHATEVER BECOMES OF THE REMNANTS OF  
ALBERTO DURING THE MIDDLE OF THE WEEK, WITH SOME CONCERN AND  
TREPIDATION GIVEN THE WET ANTECEDENT CONDITIONS ACROSS THE NC  
MOUNTAINS AND BLUE RIDGE ESCARPMENT. THE 12Z OPERATIONAL GFS  
SOLUTION REPRESENTS SOMETHING AKIN TO A WORST CASE SCENARIO WITH  
THE REMNANT CIRCULATION ESSENTIALLY TRACKING NORTHEASTWARD UP  
THE I-85 CORRIDOR ON WEDNESDAY NIGHT AND THURSDAY MORNING, WITH  
A STRONG UPSLOPE FLOW OF DEEP SUB-TROPICAL MOISTURE RESULTING IN  
POTENTIALLY SIGNIFICANT RAINFALL OVER THE MTNS AND FOOTHILLS.  
MEANWHILE, THE 12Z OPERATIONAL ECMWF IS QUITE A BIT DIFFERENT,  
WITH ITS REMNANT LOW TRACKING MORE NORTHERLY BEFORE A TURN TO  
THE NORTHEAST, THEN UP THE OH RIVER VALLEY IN THE WEDNESDAY/  
THURSDAY TIME FRAME. THIS SCENARIO WOULD STILL KEEP THE DEEP  
SUB- TROPICAL MOISTURE PLUME ACROSS THE REGION BUT WOULD BE  
POTENTIALLY LESS DIRE ACROSS THE REGION. THE WPC SOLUTION OUT  
THRU THE MEDIUM RANGE REPRESENTS SOMETHING OF A COMPROMISE  
BETWEEN THE TWO, AND WAS FOLLOWED FOR THE QPF. READERS ARE  
STRONGLY CAUTIONED NOT TO PUT TOO MUCH STOCK INTO A SINGLE MODEL  
SOLUTION THIS FAR OUT IN TIME. HOWEVER, THE CONSENSUS AT THIS  
POINT FAVORS MOVING THE REMNANT CIRCULATION TO THE WEST OF THE  
MTNS (OR PERHAPS OVER THE MTNS) DURING THE MIDDLE PART OF THE  
WEEK, SO THE THREAT WILL CONTINUE TO HANG OVER OUR HEADS THRU  
MUCH OF THE MEDIUM RANGE. AS FOR THE FORECAST, WE WILL RETAIN A  
HIGH PRECIP PROBABILITY THROUGH THURSDAY, AND THEN A TAPERING  
OFF AT THE END OF THE WEEK. TEMPS WILL REMAIN CLOSE TO NORMAL  
FOR HIGHS AND RELATIVELY MILD FOR LOWS.  
 

 
   
AVIATION /19Z FRIDAY THROUGH WEDNESDAY/
 
 
AT KCLT AND ELSEWHERE: VERY MOIST AIR MASS REMAINS IN PLACE, AND  
SHOWERS AND THUNDERSTORMS WILL ABAIN BE PREVALENT THIS AFTERNOON AND  
WILL BE MORE WIDESPREAD THAN THE PREVIOUS COUPLE DAYS, WITH A  
DECLINE AFTER DARK. CURRENT RADAR SHOWS LIGHT TO MODERATE SHOWERS  
SOUTH OF I85 ADVANCING NORTHWARD, AND THIS WILL CONTINUE AND BECOME  
STRONGER THROUGH THE AFTERNOON. LIGHTNING HAS SO FAR BEEN ABSENT,  
BUT SHOULD BEGIN IN STRONGER CELLS WITH ANOTHER HOUR OR 2 OF DAYTIME  
HEATING. LOW CIGS TO IFR LEVELS ARE EXPECTED OVERNIGHT AND SCATTERED  
SHOWERS AND THUNDERSTORMS ARE AGAIN EXPECTED SATURDAY AFTERNOON.  
WINDS WILL CONTINUE TO BE LIGHT AND SOMETIMES VARIABLE, WITH A SOUTH  
TO SOUTHWESTERLY AVERAGE DIRECTION.  
 
OUTLOOK: THE UNSETTLED PATTERN WILL CONTINUE THROUGH THE PERIOD.  
FLIGHT RESTRICTIONS WILL BE POSSIBLE AGAIN ON SATURDAY, WITH MORNING  
STRATUS AND FOG IN THE MOIST AIRMASS AND DIURNAL SHOWERS AND  
THUNDERSTORMS IN THE AFTERNOON/EVENING. TROPICAL MOISTURE WILL  
INCREASE BY THE LATE WEEKEND, FURTHER INCREASING THE FREQUENCY AND  
INTENSITY OF SHRA AND ASSOCIATED RESTRICTIONS. MORNING STRATUS/FOG  
ARE POSSIBLE EACH DAY, ESPECIALLY FOLLOWING HEAVY RAIN THE PREVIOUS  
DAY.  
 
CONFIDENCE TABLE...  
 
19-01Z 01-07Z 07-13Z 13-18Z  
KCLT HIGH 100% HIGH 100% HIGH 83% MED 71%  
KGSP HIGH 85% MED 75% LOW 51% MED 77%  
KAVL MED 78% MED 62% MED 62% HIGH 91%  
KHKY HIGH 82% MED 76% LOW 58% HIGH 89%  
KGMU HIGH 81% HIGH 80% MED 67% HIGH 82%  
KAND MED 69% MED 71% MED 62% MED 72%  
 
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...PM  
NEAR TERM...WJM  
SHORT TERM...TS  
LONG TERM...PM  
AVIATION...WJM  
 
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