930
FXUS62 KGSP 181019
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
619 AM EDT FRI SEP 18 2026
WHAT HAS CHANGED
NO SIGNIFICANT CHANGES TO FORECAST THINKING OR TRENDS. STILL
LIMITED CONFIDENCE IN THE FORECAST FOR THE MIDDLE OF NEXT WEEK.
KEY MESSAGES
1. LATE SUMMER-LIKE WEATHER CONTINUES THROUGH MONDAY, CHARACTERIZED
BY WARM AND HUMID CONDITIONS AND MAINLY AFTERNOON SHOWERS AND
THUNDERSTORMS.
2. A MOIST PATTERN PERSISTS THROUGH THE MIDDLE OF NEXT WEEK,
WITH TEMPERATURES FALLING BELOW NORMAL BY WEDNESDAY.
DISCUSSION
KEY MESSAGE 1: LATE SUMMER-LIKE WEATHER CONTINUES THROUGH MONDAY,
CHARACTERIZED BY WARM AND HUMID CONDITIONS AND MAINLY AFTERNOON
SHOWERS AND THUNDERSTORMS.
A SPRAWLING UPPER ANTICYCLONE RETROGRADES AND WEAKENS GRADUALLY
THROUGH SATURDAY. MEANWHILE, A SHORTWAVE MOVES THROUGH EASTERN
CANADA WITH BROAD SURROUNDING TROUGH REINFORCING HEIGHT FALLS OVER
THE EASTERN SEABOARD. A COLD FRONT WILL ADVANCE SOUTH THROUGH THE
CORN BELT AND LOWER OHIO VALLEY TODAY, SETTLING AS FAR SOUTH AS
NC BY EARLY SATURDAY.
DESPITE CONTINUING NORTH TO NORTHWEST WINDS, MOISTURE POOLING AHEAD
OF THE FRONT WILL RESULT IN INCREASING SURFACE DEWPOINTS TODAY,
WHICH SHOULD MAKE PROFILES FAVORABLE FOR DEEP CONVECTION. THE
FRONT ITSELF SHOULD REMAIN NORTH OF THE CWA THROUGH THE
AFTERNOON/EVENING. TEMPS WILL TREND WARMER WITH MOST PIEDMONT
LOCATIONS REACHING THE MID-90S, AND EVEN THE MOUNTAIN VALLEYS
MAY FLIRT WITH 90. 1500-2500 J/KG OF SBCAPE APPEAR A REASONABLE
BET, AND EFFECTIVE SHEAR ON THE ORDER OF 20 KT MAY ALLOW FOR
SOME CLUSTERING. SPC OUTLOOK STILL FEATURES MARGINAL RISK FOR
THE PIEDMONT, REFERENCING WATER LOADING ON ACCOUNT OF THE HIGH
PWATS. DCAPE AND SFC-MIDLEVEL DELTA-THETA-E ARE NOT PARTICULARLY
HIGH, WHICH WOULD MAKE SENSE GIVEN THE PWATS. THE SEVERE RISK
WOULD APPEAR TO BE "MARGINALLY MARGINAL." CAN'T RULE OUT LOCALLY
HEAVY RAINFALL IN THAT LIGHT EITHER, WITH STORM MOTION EXPECTED
TO BE SLOW OWING TO WEAK STEERING FLOW. AS THE FRONT ADVANCES
SOUTHWARD FRIDAY NIGHT THERE COULD BE ENOUGH CONVERGENCE/LIFT TO
SUPPORT SOME NEW CONVECTIVE DEVELOPMENT AS MUCAPE IS REALIZED,
SO POPS WILL DECLINE SLOWLY OVERNIGHT.
BY MIDDAY SATURDAY THE FRONT SHOULD HAVE SAGGED FAR ENOUGH SOUTH
TO ALLOW COOLER AIR TO REACH THE AREA ON MAINLY EASTERLY FLOW,
ASSOCIATED WITH HIGH PRESSURE CENTERED OVER THE ST LAWRENCE VALLEY,
THOUGH THAT HIGH IS TOO WEAK FOR CAD. TEMPS SHOULD FALL A FEW
DEGREES COMPARED TO FRIDAY, THOUGH STILL ABOVE-NORMAL. DRYING
ALSO MAY KEEP THE NORTHEASTERN CWA SOMEWHAT STABLE THOUGH SHOWERS
CAN'T BE TOTALLY RULED OUT. THE BEST MOISTURE WILL SHIFT TO THE
ESCARPMENT AND GA/SC ZONES, ON THE WARM SIDE OF THE FRONT, SO THE
BEST OVERALL POPS ARE LOCATED THERE. THE PRESENCE OF DRIER AIR
ALOFT SHOULD RESULT IN HIGHER DCAPE/DELTA-THETA-E, WITH SIMILARLY
HIGH SBCAPE, WHILE SHEAR IS ACTUALLY A LITTLE WEAKER. AN ISOLATED
DAMAGING MICROBURST IS NOT OUT OF THE QUESTION THERE EITHER.
SATURDAY NIGHT INTO SUNDAY THE SFC HIGH SHIFTS OFFSHORE AND ANOTHER
SHORTWAVE MOVES NORTH OF THE GREAT LAKES INTO ONTARIO/QUEBEC. THOSE
DEVELOPMENTS SUGGEST A RETURN TO SOUTHERLY LOW-LEVEL FLOW AND
THE FRONT REVERSING, ADVECTING NORTHWARD AS A WARM FRONT. THUS,
SUNDAY SHOULD BE ANOTHER WARM, HUMID AND MODERATELY UNSTABLE DAY,
SIMILAR TO SATURDAY BUT WITHOUT THE DRYING/STABILIZING EFFECT OF
THE HIGH. POPS TAKE ON A SOMEWHAT MORE CLIMATOLOGICAL PATTERN WITH
THE SOUTHERLY FLOW REGIME, BEING HIGHEST NEAR THE ESCARPMENT. THE
SAME GENERAL PATTERN LASTS INTO MONDAY OVER OUR AREA, WITH SIMILAR
SENSIBLE WEATHER ALTHOUGH TEMPERATURES LOOK TO MODERATE A FEW
DEGREES WARMER.
KEY MESSAGE 2: A MOIST PATTERN PERSISTS THROUGH THE MIDDLE OF NEXT
WEEK, WITH TEMPERATURES FALLING BELOW NORMAL BY WEDNESDAY.
THE PATTERN IS BEST DESCRIBED AS UNUSUAL BY TUESDAY; NOT TERRIBLY
CONFIDENT ON EXACTLY HOW IT MIGHT EVOLVE. A STRONG CANADIAN SURFACE
HIGH WILL BE COMING INTO POSITION TO FOSTER COLD-AIR DAMMING ALONG
THE EASTERN SEABOARD BY TUESDAY, BUT ALSO A TRAILING SHORTWAVE SET
TO CUT OFF AND FORM BASICALLY A REX BLOCK CENTERED OVER THE GREAT
LAKES. THIS LEAVES A WAVERING FRONT WELL TO OUR NORTH. NORTHEAST
FLOW APPEARS TO DEVELOP TUESDAY, AND TEMPERATURES DO TREND COOLER
THOUGH THAT MAY JUST BE DUE TO CLOUDS AND PRECIP AFFORDED BY
SOUTHERLY AND/OR ONSHORE FLOW. FOR WEDNESDAY THE SURFACE HIGH
MIGRATES SLIGHTLY FARTHER EAST AND THE PRESSURE PATTERN IN OUR AREA
WOULD APPEAR TO INDICATE CAD WILL HAVE DEVELOPED, WITH CONTINUED
ELEVATED CHANCES FOR PRECIP GIVEN OUR POSITION SO FAR SOUTH OF THE
WARM FRONT. TEMPS SHOULD TOP OUT A FEW DEGREES BELOW NORMAL THAT
DAY, THOUGH GIVEN THE COMPLEX PATTERN IT'S HARD TO BE CONFIDENT
ON GOING AS FAR BELOW NORMAL AS THE COOLEST MODELS SUGGEST. THE
CUTOFF LOW IN THE MIDWEST LOOKS TO FORM A SURFACE WAVE ALONG THE
FRONTAL ZONE; WHILE THE DAMMING HIGH BECOMES DISTANT BY THURSDAY,
THAT LOW IS IN POSITION TO ACTIVATE A COLD FRONT AND PULL IT ACROSS
THE APPALACHIANS, WHICH WOULD REINFORCE BELOW-NORMAL TEMPS THURSDAY
AND A DRYING TREND LATER IN THE WEEK.
AVIATION /10Z FRIDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: WINDS REMAIN LIGHT AND VRB, BUT SHOULD
PICK UP N/NE BY EARLY MORNING. BR LIKELY AT KAVL SO TEMPO THROUGH
13Z. TSRA POSSIBLE AT ALL SITES THIS AFTERNOON. PROB30 FOR ALL
SITES. VCSH MAY LINGER AFTER 00Z AT KCLT. MAY START TO SEE LOW
STRATUS AND MVFR/IFR VSBY FOR THE MOUNTAIN TERMINALS AND CIGS
ELSEWHERE MOVING IN TOWARD DAYBREAK. KCLT SHOULD IMPROVE TO VFR CIGS
AT THE END OF THE TAF PERIOD.
OUTLOOK: SHOWER AND THUNDERSTORM CHANCES CONTINUE EACH AFTERNOON
THROUGH TUESDAY. MOUNTAIN VALLEY FOG AND LOW STRATUS POSSIBLE EACH
MORNING.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
CP/JCW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page