594  
FXUS62 KGSP 211818  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
118 PM EST THU FEB 21 2019  
   
SYNOPSIS
 
 
CHILLY HIGH PRESSURE ATOP THE REGION WILL WEAKEN TODAY AS A SERIES  
OF LOW PRESSURE SYSTEMS MOVES UP FROM THE GULF. THE MOIST PATTERN  
WILL CONTINUE WELL INTO THE WEEKEND UNTIL A COLD FRONT FINALLY MOVES  
THROUGH THE REGION SUNDAY. AFTER A BRIEF BREAK EARLY NEXT WEEK,  
ANOTHER SYSTEM WILL APPROACH BY MID-WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 115 PM: MAIN UPDATE FOR THE 18Z TAF ISSUANCE, ALONG WITH  
MINOR ADJUSTMENTS TO TEMPS/POPS/WINDS TO COINCIDE WITH LATEST  
TRENDS, AS THE REST OF THE NEAR TERM FORECAST REMAINS ON TRACK.  
CONDITIONS HAVE QUIETED DOWN OVER THE PAST FEW HOURS WITH  
OVERALL BREAKS IN THE CLOUDS. DO EXPECT THIS LULL IN  
PRECIPITATION WILL BE BRIEF, WITH CLOUDS FILLING BACK IN THIS  
EVENING, AND PRECIP CHANCES RETURNING TONIGHT.  
 
OTHERWISE, RAINFALL FROM OVERNIGHT HAS CAUSED NUMEROUS STREAM GAUGES  
TO RISE INTO ADVISORY-LEVEL LEVELS, WITH SOME MINOR FLOODING IN  
SPOTS. THUS, A FLOOD WATCH REMAINS IN EFFECT FOR PORTIONS OF THE  
AREA. WITH A LULL IN PRECIP ALONG WITH A LACK OF ANY PARENT HIGH,  
EXPECT AN EROSION OF THE CAD. HOWEVER, THE COLD POOL DOESN'T  
COMPLETELY SCOUR (AS THE INVERSION IS VERY STRONG), AND WITH LITTLE  
BREAK IN THE LOW OVERCAST, TEMPS SHOULD ONLY WARM INTO THE 50S TO  
AROUND 60 (DESPITE WHAT OTHER GUIDANCE LIKE THE GFS SUGGESTING MID  
TO UPPER 60S).  
 
TONIGHT, THE RIGHT ENTRANCE REGION OF THE 300 MB JET PIVOTS BACK  
OVER OUR AREA AGAIN AND WILL BE COUPLED WITH INCREASED 850 MB WAA  
AND STRONG 850-700 MB FRONTOGENESIS. THIS FORCING WILL ALSO BE ATOP  
A NEW COLD AIR DAMMING WEDGE, AS A 1032 MB SFC HIGH BUILDS OVER THE  
GREAT LAKES AND PUSHES A BACKDOOR COLD FRONT THRU THE AREA. POPS  
RAMP BACK UP TO LIKELY TO CATEGORICAL. THERE WILL BE SOME MUCAPE  
ATOP THE WEDGE, BUT NOT AS MUCH AS THIS MORNING. STILL COULD SEE  
ISOLATED ELEVATED THUNDER IN THE SOUTHERN ZONES OVERNIGHT. PRECIP  
RATES WILL PICK UP, AND EVEN MODEST 0.5-1.0" TOTALS MAY CAUSE SOME  
RAPID STREAM RISES. IN ANY CASE, HYDRO CONCERNS WILL CONTINUE TO  
INCREASE WITH EACH ADDITIONAL ROUND OF RAIN. TEMPS WILL COOL A  
LITTLE WITH CAD AND PRECIP, BUT REMAIN ABOVE NORMAL (MAINLY IN THE  
40S TO LOWER 50S).  
 

 
   
SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/
 
 
AS OF 245 AM EST THURSDAY: THE SHORT TERM PERIOD BEGINS FRIDAY  
MORNING WITH THE RECURRING PATTERN OF DAMMING-ISENTROPIC UPGLIDE-  
RAIN-YUCK. SURFACE HIGH OVER THE GREAT LAKES WILL BE DAMMING DOWN AT  
THE BEGINNING OF THE PERIOD WITH A SLUG OF MOISTURE LIFTING UP OVER  
THE WESTERN ATLANTIC RIDGE. RECENT GUIDANCE TRENDS HAVE INCREASED  
THE STRENGTH OF THE DAMMING AND THIS REMAINS THE CASE, THOUGH THE  
LOW-LEVEL CAA WON'T BE COLD ENOUGH FOR ANY P-TYPE ISSUES. INSTEAD,  
THE PRIMARY CONCERN WILL BE THE CONTINUED RAINFALL. AT LEAST  
INITIALLY, THE HEAVIEST RAIN WILL BE OVER THE MOUNTAINS ALONG THE  
MOISTURE AXIS, BUT THE UPPER RIDGE AXIS WILL BEGIN TO MOVE EAST  
THROUGH THE DAY IN RESPONSE TO A DEEP LOW EJECTING OUT OF THE  
ROCKIES, ALLOWING ISENTROPIC UPGLIDE TO RESULT IN A PROLONGED PERIOD  
OF LIGHT RAIN, POSSIBLY DRIZZLE, OFF AND ON DURING THE DAY (AS IF WE  
HAVEN'T HAD ENOUGH CLOUDY COLD RAINY MISERABLE YUCKY DAYS LATELY).  
QPF IS NOT PARTICULARLY IMPRESSIVE ON FRIDAY, GENERALLY 1/2" OR SO,  
BUT SOILS ARE VERY SATURATED AND WITH NEAR-TERM RAIN, FELT IT  
PRUDENT TO GO AHEAD AND TAKE THE FLOOD WATCH THROUGH THE DAY FRIDAY,  
AND WILL REEVALUATE IN LATER SHIFTS WHETHER OR NOT IT NEEDS TO BE  
EXTENDED (OR EXPANDED) FURTHER.  
 
LITTLE DIURNAL RANGE INTO FRIDAY NIGHT, AND VERY LITTLE CHANGE INTO  
SATURDAY FOR TEMPERATURES. HOWEVER, AS THE WAVE AMPLITUDE INCREASES  
IN RESPONSE TO THE NOW-PLAINS UPPER LOW, THE MOISTURE AXIS WILL BE  
SHUNTED NORTH, RESULTING IN A LITTLE BIT OF A LULL SATURDAY  
AFTERNOON.  
 
AS THE APPROACHING SURFACE LOW OCCLUDES AND THE UPPER SYSTEM FILLS  
AND LIFTS RAPIDLY NORTHEAST, THE ATTENDANT FRONT WILL APPROACH  
SATURDAY NIGHT. RESIDUAL COOL POOL WILL TRY ITS HARDEST TO REMAIN  
ENTRENCHED UP AGAINST THE BLUE RIDGE, BUT THE STRONG FRONT WILL  
RAPIDLY SCOUR THE DAMMING OUT OVERNIGHT SATURDAY NIGHT INTO EARLY  
SUNDAY, WITH THE FRONT BASICALLY CLEARING THE AREA BY MIDDAY SUNDAY  
(WITH THE THUNDERSTORM THREAT BASICALLY NIL FOR OUR AREA DUE TO THE  
TIMING). HUGE DIFFERENCE WITH THE ERODED DAMMING AND JUST BEFORE THE  
FRONTAL PASSAGE, AS SOUTHWESTERLY LOW-LEVEL FLOW WILL BRING SOME  
STRONG AIRMASS RECOVERY TO THE AREA BEFORE THE POST-FRONTAL CAA  
PICKS UP. PRESSURE GRADIENT WILL RESULT IN A BIT OF A BREEZE SUNDAY,  
BUT HIGHS NEAR 70 IN THE PIEDMONT (50S TO NEAR 60 IN THE MOUNTAINS -  
ALL A GOOD 10-20 DEGREES WARMER THAN FRI AND SAT) WILL RESULT IN A  
REALLY REALLY BEAUTIFUL DAY. OF COURSE, THE DIURNAL RANGE RETURNS  
WITH LOWS SUNDAY NIGHT PRETTY CLOSE TO SEASONAL NORMALS.  
 

 
   
LONG TERM /MONDAY THROUGH WEDNESDAY/
 
 
AS OF 300 AM EST THURSDAY: POST-FRONTAL CONDITIONS EARLY IN THE WORK  
WEEK WILL BE PLEASANT, THOUGH WITH A COOLING TREND BACK TO SEASONAL  
NORMALS FOR HIGHS AND LOWS EARLY-ON. EXPECT A NICE DAY ON MONDAY,  
ANOTHER GREAT OPPORTUNITY TO SOAK UP SOME SUNSHINE AFTER THE WEEK OF  
GLOOM. TOWARD THE LATTER PART OF THE WEEK, MODEL DIFFERENCES  
INCREASE, BUT THE OVERALL PICTURE IS THAT ANOTHER SYSTEM IN THE  
NORTHERN STREAM WILL APPROACH TUESDAY INTO WEDNESDAY, POSSIBLY  
PHASING WITH A SOUTHERN STREAM WAVE. THE ECMWF KEEPS THE TWO SYSTEMS  
SEPARATE, LEAVING US IN MUCH DRIER CONDITIONS, WHEREAS THE GFS  
PHASES THE TWO AND BRINGS MOISTURE BACK INTO THE AREA TUESDAY NIGHT.  
HAVE KEPT A BLEND WITH SOME LOW-END POPS.  
 

 
   
AVIATION /18Z THURSDAY THROUGH TUESDAY/
 
 
AT KCLT AND ELSEWHERE: A MIXTURE OF VFR/MVFR/IFR PREVAILS ACROSS THE  
AREA THIS AFTERNOON, WITH SOME BREAKS IN THE CLOUDS, THOUGH THE CAD/  
LOW-LEVEL INVERSION HAS YET TO DISSIPATE COMPLETELY. DESPITE THE  
IMPROVED CONDITIONS IN SOME LOCATIONS, DO ANTICIPATE LOWERING CIGS  
AND INCREASING PRECIPITATION CHANCES TO RETURN WITH IFR TONIGHT WITH  
A BACKDOOR COLD FRONT. GIVEN LOWER CONFIDENCE ON EXACT TIMING OF  
EXPECTED CONDITIONS, HAVE KEPT WITH A GENERAL TREND OF SLOWLY  
DETERIORATING CONDITIONS TONIGHT, CONTINUING THROUGH THE END OF THE  
VALID TAF PERIOD. EXPECT SW WINDS 5 TO 7 KTS THIS AFTERNOON TO  
BECOME NE LATE TONIGHT, AOB 5 KTS, WITH THE EXCEPTION OF KAVL, WHERE  
CURRENT NW WINDS WILL BECOME NE.  
 
OUTLOOK: A SERIES OF LOW PRESSURE SYSTEMS WILL CONTINUE TO MOVE  
THROUGH THE REGION THROUGH THE END OF THE WEEK. THIS WILL PRODUCE  
PRECIPITATION AND ASSOCIATED RESTRICTIONS FOR LONG PERIODS OF TIME  
WITH EACH SYSTEM. A COLD FRONT IS EXPECTED TO DRY OUT THE REGION  
SUNDAY.  
 
CONFIDENCE TABLE...  
 
18-24Z 00-06Z 06-12Z 12-18Z  
KCLT HIGH 85% MED 69% MED 75% MED 71%  
KGSP HIGH 88% HIGH 87% HIGH 88% HIGH 86%  
KAVL MED 79% HIGH 85% HIGH 94% HIGH 89%  
KHKY MED 78% HIGH 83% MED 75% MED 74%  
KGMU HIGH 89% HIGH 88% HIGH 85% MED 79%  
KAND HIGH 90% HIGH 82% MED 75% HIGH 81%  
 
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...FLOOD WATCH THROUGH FRIDAY EVENING FOR GAZ010-017-018-026-028.  
NC...FLOOD WATCH THROUGH FRIDAY EVENING FOR NCZ048-051>053-058-059-  
062>065-509-510.  
SC...FLOOD WATCH THROUGH FRIDAY EVENING FOR SCZ001>007-010.  
 

 
 

 
SYNOPSIS...TDP  
NEAR TERM...ARK/SGL  
SHORT TERM...TDP  
LONG TERM...TDP  
AVIATION...SGL  
 
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