140
FXUS62 KGSP 301056
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
656 AM EDT SAT AUG 30 2025
SYNOPSIS
COOLING HIGH PRESSURE BUILDS INTO THE AREA TODAY AND CONTINUES
INTO EARLY NEXT WEEK. ISOLATED TO WIDELY SCATTERED SHOWERS
AND FEW THUNDERSTORMS WILL BE POSSIBLE EACH DAY ACROSS THE
MOUNTAINS. TEMPERATURES REMAIN BELOW SEASONAL NORMALS THROUGH
THE WEEK.
NEAR TERM /THROUGH TONIGHT/
AS OF 230 AM EDT SATURDAY: SURFACE ANALYSIS EARLY THIS MORNING
DEPICTS EXPANSIVE HIGH PRESSURE CENTERED OVER THE GREAT LAKES,
WITH A WEAK, DIFFUSE COLD FRONT DRAPED ALONG ITS SOUTHEASTERN
PERIPHERY. WINDS ARE GENERALLY CALM, BUT A SUBTLE 3-5F
TEMPERATURE/DEWPOINT GRADIENT HELPS PLACE THE BOUNDARY ACROSS THE
FAR SOUTHEASTERN CWA, ROUGHLY FROM THE LOWER PIEDMONT OF SC INTO THE
EASTERN PIEDMONT OF NC. ALOFT, ANOMALOUS TROUGHING CONTINUES OVER
THE EASTERN CONUS AS A CLOSED LOW LINGERS OVER THE NORTHEAST. THIS
FEATURE WILL GRADUALLY OPEN AND LIFT TOWARD COASTAL NEW ENGLAND
LATER TODAY, THOUGH ADDITIONAL SHORTWAVES ROTATING AROUND ITS BASE
WILL REINFORCE TROUGHING ACROSS THE REGION.
ONE SUCH PERTURBATION IS MOVING OVERHEAD EARLY THIS MORNING,
PRODUCING MID-LEVEL CLOUD COVER. EARLIER FORECASTS CARRIED SLIGHT
CHANCE POPS BEFORE DAYBREAK, BUT THESE WERE REMOVED GIVEN LIMITED
LOW-LEVEL MOISTURE AND WEAK FRONTAL FORCING.
BY DAYBREAK, A LIGHT NORTHEAST WIND WILL DEVELOP AS THE BOUNDARY
STALLS NEAR THE LOWER PIEDMONT/MIDLANDS (BETWEEN ROUGHLY GREENWOOD
AND COLUMBIA). VEERING FLOW THROUGH THE COLUMN WILL PROMOTE EASTERLY
UPSLOPE ALONG THE BLUE RIDGE BY THIS AFTERNOON. MEANWHILE, THE
NEXT SHORTWAVE APPROACHES, PROVIDING MODEST MID-LEVEL SUPPORT. THIS
SETUP SUPPORTS SCATTERED SHOWERS (30 POPS) ACROSS THE SOUTHERN AND
CENTRAL MOUNTAINS. INSTABILITY REMAINS MEAGER NORTH OF THE FRONT,
AND MODEL SOUNDINGS CONTINUE TO SHOW A SHALLOW BUOYANT LAYER CAPPED
BY A MID-LEVEL INVERSION. DESPITE A POCKET OF COOLER AIR ALOFT WITH
THE TROUGH PASSAGE, EQUILIBRIUM LEVELS NEAR –5C ARGUE STRONGLY
AGAINST THUNDER POTENTIAL, SO POT THUNDER HAS BEEN REMOVED.
TONIGHT, SURFACE HIGH PRESSURE BUILDS EASTWARD ACROSS THE OHIO
VALLEY, WITH RIDGING EXTENDING SOUTHWARD ALONG THE EASTERN
APPALACHIANS. THE STRENGTHENING EAST-SOUTHEAST FLOW ABOVE THE
NOCTURNAL BOUNDARY LAYER SHOULD FAVOR STRATUS DEVELOPMENT ALONG
THE ESCARPMENT, THOUGH CEILINGS MAY HOLD OFF UNTIL CLOSER TO
DAYBREAK SUNDAY.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
AS OF 130 AM EDT SATURDAY: ANOTHER LOBE OF VORTICITY WILL ROTATE
THRU A DEEP LONGWAVE TROUGH OVER THE EASTERN CONUS AND CROSS THE
CENTRAL AND SOUTHERN APPALACHIANS ON SUNDAY. THIS WILL HELP STEEPEN
MID- LEVEL LAPSE RATES ENOUGH TO ALLOW FOR BETTER INSTABILITY
SUN AFTN, ESP ACROSS THE MOUNTAINS. OTHERWISE, PWATS INCREASE
SLIGHTLY BUT REMAIN MODEST AT 0.8 TO 1.4" ACROSS THE AREA FROM
NORTH TO SOUTH. AT THE SFC, A 1025 MB HIGH WILL SET UP OVER THE
NORTHEAST, AND WILL KEEP A WEDGE-LIKE PATTERN OVER THE FORECAST
AREA. EASTERLY LOW-LEVEL FLOW WILL HAVE ENOUGH MOISTURE FOR SOME
STRATUS DEVELOPMENT EARLY SUNDAY, BUT SHOULD MOSTLY SCATTER OUT
IN THE AFTN. ISOLATED TO SCATTERED CONVECTION IS EXPECTED ACROSS
THE MOUNTAINS IN THE AFTN TO EARLY EVENING. STEERING FLOW WILL
TRY TO TAKE THIS ACTIVITY INTO THE PIEDMONT, BUT WITH LIMITED
INSTABILITY, WILL MOSTLY DISSIPATE. WHATEVER STORMS DO DEVELOP
WILL LIKELY STRUGGLE TO BE STRONG OR SEVERE, GIVEN THE MODEST
CAPE. BUT CANNOT BE COMPLETELY RULED OUT WITH 30-35 KT OF BULK
SHEAR AND SOME UPPER SUPPORT WITH THE PASSING VORT LOBE. HIGHS
WILL BE AROUND 4 TO 8 DEG BELOW NORMAL.
MODELS GENERALLY AGREE ON A LARGE UPPER LOW CLOSING OFF OVER THE
MID- ATLANTIC MONDAY, BUT WITH SHORTWAVE ENERGY DIVING INTO THE
WESTERN SIDE OF THE CIRCULATION KEEPING THE FLOW FAIRLY FLAT OVER
THE SOUTHEAST. THE 850 MB FLOW BACKS TO MORE NELY AND ADVECTS
SOME DRIER AIR, WHILE THE INVERTED SFC RIDGE HOLDS ON ALONG THE
EAST COAST. OVERALL, THIS RESULTS IN LOWER POPS AND CONTINUED
BELOW-NORMAL TEMPS. SOME SHOWERS MAY DEVELOP IN THE MOUNTAINS,
BUT THE PIEDMONT WILL HAVE SUB-15% POPS.
LONG TERM /TUESDAY THROUGH FRIDAY/
AS OF 155 AM EDT SATURDAY: A VIGOROUS UPPER SHORTWAVE WILL CARVE
OUT A NEW TROUGH AND MERGE WITH THE PERSISTENT EASTERN CONUS
LONGWAVE TROUGH TUESDAY INTO WEDNESDAY. THEN, AN EVEN STRONGER
SHORTWAVE/COMPACT LOW WILL DROP SOUTH THRU THE UPPER MIDWEST FURTHER
DEEPEN THE TROUGH OVER THE OHIO VALLEY THURSDAY INTO FRIDAY. THE
FIRST TROUGH WILL BRING DEEP-LAYER Q-VECTOR CONVERGENCE TUESDAY
NIGHT THRU WEDNESDAY. THE SECOND WAVE KEEPS THE STRONGEST ENERGY
NORTH OF THE FORECAST AREA, BUT MAY PROVIDE SOME UPPER SUPPORT
FOR PRECIP. THE BIG DISAGREEMENT AMONG THE DETERMINISTIC MODELS
IS HOW MUCH MOISTURE THESE TROUGHS WILL TAP INTO AS THEY PASS
BY. THE 12Z ECMWF HAS MORE MOISTURE AND A STRONGER SFC LOW FORM
ALONG A STALLED FRONT IN THE GULF THAT TRACKS ALONG THE CAROLINA
COAST WEDNESDAY. THIS WOULD SPREAD IN MORE PRECIP CHANCES EAST
OF THE MOUNTAINS COMPARED TO THE DRIER GFS AND CANADIAN. NONE
OF THE GUIDANCE IS TOO EXCITED ABOUT PRECIP CHANCES WITH THE
FOLLOWING COLD FRONT ASSOCIATED WITH THE DEEP TROUGH THURSDAY
THRU FRIDAY. MOISTURE/POPS WILL MAINLY JUST BRUSH THE NC MOUNTAINS
FROM THE WEST. TEMPS WILL REMAIN WELL BELOW NORMAL THRU THE PERIOD
GIVEN THE DEEP UPPER TROUGHINESS PERSISTING ACROSS THE REGION.
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE: MID AND HIGH CLOUDS HAVE OVERSPREAD THE
REGION OVERNIGHT AS A SHORTWAVE PASSES THROUGH. THIS SHOULD INHIBIT
FOG FROM FORMING AS WE APPROACH SUNRISE THIS MORNING. ALL TERMINALS
ARE EXPECTED TO REMAIN VFR TODAY. WINDS ARE CURRENTLY CALM BUT WILL
BECOME LIGHT NE (NW AT KAVL) AROUND 4-6 KT BY MID TO LATE MORNING,
VEERING E THIS AFTERNOON AND SE BY EVENING. A DIURNAL CU FIELD
SHOULD DEVELOP IN THE AFTERNOON, THOUGH COVERAGE MAY BE DELAYED BY
MORNING CLOUDINESS AND LIMITED BOUNDARY-LAYER MOISTURE. RESULTING
SCT–BKN CEILINGS WILL GENERALLY RANGE 4-7 KFT. ISOLATED SHOWERS
WILL MAINLY AFFECT THE MOUNTAINS, ESPECIALLY ALONG EAST-FACING
SLOPES OF THE BLUE RIDGE. ANY IMPACTS TO KAVL REMAIN TOO UNCERTAIN
FOR EVEN A PROB30 MENTION AT THIS TIME.
FOR TONIGHT, MODELS SUGGEST PATCHY MOUNTAIN VALLEY FOG WITH
PROBABILITIES FOR < 5SM AT KAVL NEAR 40 PERCENT. HOWEVER,
CONFIDENCE REMAINS LOW GIVEN PERSISTENT MID-LEVEL CLOUDS AND
STRENGTHENING EASTERLY FLOW ASSOCIATED WITH A WEAK COLD-AIR
DAMMING SETUP. STRATUS DEVELOPMENT ALONG AND EAST OF THE BLUE RIDGE
ESCARPMENT APPEARS MORE LIKELY THAN VALLEY FOG. A MVFR GROUP FOR
CIGS WAS INTRODUCED IN THE 12Z TAFS FOR THE END OF THE TAF PERIOD,
(NOT ENOUGH CONFIDENCE TO GO IFR AT THIS POINT).
OUTLOOK: SCATTERED AFTERNOON/EVENING CONVECTION RETURNS EARLY
NEXT WEEK, MAINLY ACROSS THE MOUNTAINS, AND PERSISTS THROUGH
MIDWEEK. NOCTURNAL VALLEY FOG AND/OR LOW STRATUS WILL ALSO BE
POSSIBLE EACH NIGHT AND EARLY MORNING, ESPECIALLY ACROSS MOUNTAIN
LOCATIONS.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...ARK
NEAR TERM...JK
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...JK
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