345
FXUS62 KGSP 280720
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
320 AM EDT TUE JUL 28 2026
WHAT HAS CHANGED
MORE DETAILS TO DIFFERENTIATE THE POSSIBLE MORNING CONVECTIVE
ACTIVITY FROM THE MAIN, MORE LIKELY SEVERE ROUND THIS AFTERNOON.
KEY MESSAGES
1. ANY THUNDERSTORMS DEVELOPING AHEAD OF A COLD FRONT TODAY AND
THIS EVENING WILL POSE A RISK OF SEVERE WEATHER, THOUGH CONFIDENCE
REMAINS LOW ON HOW MUCH OF THE AREA WILL SEE THUNDERSTORMS
DEVELOP. THE MAIN HAZARDS WITH ANY SEVERE STORMS ARE DAMAGING
WINDS AND LARGE HAIL. MAKE SURE YOU HAVE MULTIPLE WAYS TO RECEIVE
WARNINGS.
2. HOT AND HUMID TODAY. A HEAT ADVISORY REMAINS IN EFFECT
FOR NORTHEAST GEORGIA FROM NOON TO 8 PM. STAY HYDRATED, LIMIT
TIME OUTDOORS AND SPEND AS MUCH TIME IN AIR CONDITIONING AS
POSSIBLE. NEVER LEAVE PEOPLE OR PETS ALONE IN A CLOSED CAR. LOOK
BEFORE YOU LOCK!
3. LESS HUMID, DRIER, AND COOLER BEHIND THE FRONT WEDNESDAY
THROUGH FRIDAY. EVEN COOLER CONDITIONS EXPECTED OVER THE WEEKEND
WITH SHOWER AND THUNDERSTORM CHANCES RETURNING.
DISCUSSION
KEY MESSAGE 1: ANY THUNDERSTORMS DEVELOPING AHEAD OF A COLD FRONT
TODAY AND THIS EVENING WILL POSE A RISK OF SEVERE WEATHER,
THOUGH CONFIDENCE REMAINS LOW ON HOW MUCH OF THE AREA WILL SEE
THUNDERSTORMS DEVELOP. THE MAIN HAZARDS WITH ANY SEVERE STORMS
ARE DAMAGING WINDS AND LARGE HAIL. MAKE SURE YOU HAVE MULTIPLE
WAYS TO RECEIVE WARNINGS.
WE'LL HAVE MORE DAY IN THE ACTIVE, NORTHWEST-FLOW "RING OF FIRE"
PATTERN WE HAVE BEEN LOCKED INTO SINCE LATE LAST WEEK. AN MCS
DECAYED LATE MON EVENING OVER KY AND SOME OF ITS CIRRUS SHIELD
IS ADVECTING OVER THE AREA NOW; ASIDE FROM A FEW REMNANT SHOWERS
OVER THE NC MOUNTAINS, IT APPEARS UNLIKELY PRECIP WILL DEVELOP IN
OUR AREA BEFORE DAYBREAK.
A WELL DEFINED SHORTWAVE AND SURFACE LOW NOW BETWEEN LAKES
MICHIGAN AND ERIE IS ASSOCIATED WITH A COLD FRONT WHICH WILL TRACK
THROUGH THE OHIO VALLEY EARLY THIS MORNING. NEAR THE SHORTWAVE,
A COUPLE CLUSTERS OF STORMS ARE ALREADY ONGOING, AND THAT
ACTIVITY COULD CONGEAL INTO AN MCS WHICH WOULD PRIMARILY TRACK
TO OUR NORTH. HOWEVER, PRECEDING THE COLD FRONT, A STRONG LLJ IS
PROMOTING WAA NEAR THE OHIO RIVER, AND AS THE FRONT APPROACHES
CONDITIONS APPEAR FAVORABLE FOR A NEW ROUND OF STORMS TO FIRE ON
THE SOUTHWEST FLANK OF THE MCS, PROPAGATING SOUTHWARD AHEAD OF THE
ACTUAL FRONT. THERE IS A CHANCE THOSE STORMS COULD SURVIVE INTO THE
NC MOUNTAINS DURING THE MORNING, THOUGH CAMS APPEAR TO BE TRENDING
AWAY FROM THE IDEA OF THEM GROWING INTO A LINE AS SOME EARLIER RUNS
(AS RECENTLY AS THE 00Z NAMNEST AND HRRR) SUGGESTED. EVEN IF THE
CELLS ARE WEAK OR DISCRETE THE NBM POPS APPEARED TOO LOW TO REFLECT
THEIR POSSIBILITY. THUS, POPS HAVE BEEN RAISED OVER WESTERN NC AND
ADJACENT AREAS OF SC/GA THROUGH MIDDAY. ANOMALOUSLY STRONG FLOW
IN THE 700-500MB LAYER LEADS TO EFFECTIVE SHEAR PERHAPS EXCEEDING
40 KT ALONG/WEST OF THE APPALACHIANS THIS MORNING, AND 2000 J/KG
OR MORE OF MUCAPE MAY BE PRESENT. THUS THERE WOULD APPEAR TO BE
SOME RISK OF ORGANIZED SEVERE WEATHER WITH THIS MORNING ACTIVITY,
THOUGH THE NORTHERLY SHEAR VECTORS DO SUGGEST UPDRAFTS MAY REMAIN
DISCRETE AND COULD DEVELOP INTO SUPERCELLS.
CLOUD COVER ASSOCIATED WITH THE PREFRONTAL WAA, AND/OR CIRRUS
DEBRIS FROM THE MORNING STORMS, STILL COULD INHIBIT CONVECTIVE
DEVELOPMENT LATER IN THE DAY, THOUGH WITHOUT A STRONG COLD POOL
FROM AN MCS IT'S HARD TO SEE THAT COMPLETELY INHIBITING ENOUGH
DIURNAL DESTABILIZATION TO PRECLUDE A SECOND ROUND OF ACTIVITY
NEARER THE ACTUAL COLD FRONT, THIS AFTERNOON AND EVENING. POPS
ARE LOWER IN THE AFTERNOON FOR THE SOUTHWEST QUADRANT OF THE CWA,
WHERE THE MORNING ACTIVITY (AND ARGUABLY STRONG DOWNSLOPE FLOW)
HAS THE MOST POTENTIAL TO KEEP THINGS QUIET. POPS ARE HIGHEST IN
THE AFTERNOON ALONG THE TN BORDER FOR UPSLOPE, BUT ALSO IN THE
EASTERN PIEDMONT SOUTH OF I-85, WHERE MORNING ACTIVITY IS LIKELY TO
HAVE THE LEAST EFFECT. HOWEVER WE WILL HAVE TO MONITOR CONVECTIVE
TRENDS AND SURFACE OBS THROUGHOUT THE MORNING TO EVALUATE THE
LIKELIHOOD OF THE SECOND ROUND TAKING SHAPE. BY LATE AFTERNOON OR
EARLY EVENING, ASSUMING NO INHIBITION, 2000-3000 J/KG OF SBCAPE
STILL MAY OVERLAP WITH 40+ KT OF NORTHWESTERLY 0-6KM BULK SHEAR
(AND STRONGLY CURVING HODOGRAPHS). AS THE COLD FRONT LOOKS TO
ADVANCE SE'WD THROUGH THE NC PIEDMONT ACCOMPANIED BY THE SHORTWAVE,
DISCRETE SUPERCELLS REMAIN THE FAVORED MODE THERE. DAMAGING WINDS
AND LARGE HAIL PERHAPS APPROACHING 2" IN DIAMETER ARE CERTAINLY
ON THE TABLE THIS AFTERNOON, BUT 0-1KM HELICITY EXCEEDS 100 M2/S2
IN SOME AREAS AND A TORNADO CANNOT BE RULED OUT. FARTHER WEST,
THE FRONTAL ORIENTATION IS MORE E-W AND A MORE LINEAR MODE MAY
RESULT, THOUGH STILL WITH WIND/HAIL RISK FROM EMBEDDED SUPERCELL
STRUCTURES. SPC DAY 1 OUTLOOK REMAINS SLIGHT RISK FOR VIRTUALLY
THE WHOLE CWA, BUT WITH THE PROBABILISTIC CONTOURS MORE SUGGESTIVE
OF THE GREATEST THREAT BEING IN OUR EASTERN ZONES.
KEY MESSAGE 2: HOT AND HUMID TODAY. A HEAT ADVISORY REMAINS IN EFFECT
FOR NORTHEAST GEORGIA FROM NOON TO 8 PM. STAY HYDRATED, LIMIT TIME
OUTDOORS AND SPEND AS MUCH TIME IN AIR CONDITIONING AS POSSIBLE.
NEVER LEAVE PEOPLE OR PETS ALONE IN A CLOSED CAR. LOOK BEFORE
YOU LOCK!
STILL EXPECTING TODAY TO BE THE HOTTEST AND MOST HUMID DAY THIS
WEEK. HEAT INDEX WILL FLIRT WITH 105 IN A FEW SCATTERED LOCATIONS
IN THE LOWER PIEDMONT; THE CONTIGUOUS AREA OF 105+ HEAT INDICES
IN A PORTION OF NE GA WARRANTED ISSUANCE OF A HEAT ADVISORY
THERE. CONSIDERED EXPANSION INTO SOME COUNTIES IN THE SC LAKELANDS,
BUT THERE IS TOO MUCH UNCERTAINTY ABOUT HOW MORNING CONVECTION
MAY AFFECT TEMPERATURES THERE AND ELSEWHERE IN THE PIEDMONT FOR
THAT MATTER.
KEY MESSAGE 3: LESS HUMID, DRIER, AND COOLER BEHIND THE FRONT
WEDNESDAY THROUGH FRIDAY. EVEN COOLER CONDITIONS EXPECTED OVER
THE WEEKEND WITH SHOWER AND THUNDERSTORM CHANCES RETURNING.
BEHIND THE FRONT, TEMPERATURES TREND BACK TO AROUND CLIMO ON
WEDNESDAY, WITH LOWER HUMIDITY THAT SHOULD KEEP INDICES BELOW 100,
AND MUCH MORE STABLE CONDITIONS SUCH THAT PRECIP CHANCES REMAIN NEAR
ZERO, EXCEPT FOR THE TN/NC BORDER AREA WHERE UPSLOPING COULD KICK
OFF A SHOWER OR TWO. APPRECIABLY DRIER AIR FILTERS IN FOR THURSDAY
THAT BRINGS TEMPS SLIGHTLY LOWER BUT HEAT INDICES MORE NOTICEABLY
LOWER. SIMILAR CONDITIONS LAST THROUGH FRIDAY. THE UPSTATE AND NE
GA, BEING WARMER, ACTUALLY SEE RH FALL TO AROUND 35% THURSDAY AND
FRIDAY, WHICH IS EXCEPTIONALLY LOW FOR THIS TIME OF YEAR. A FEW
SPOTS WITH ENHANCED MIXING COULD GO EVEN LOWER.
THE WESTERN RIDGE / EASTERN TROUGH PATTERN LINGERS INTO NEXT
WEEKEND, THOUGH NOT AS UNSTABLE UPSTREAM AND MCS THREATS DO
NOT LOOK TO RECUR. PRECIP/STORMS MAY RETURN SATURDAY, WHEN A
REINFORCING SHORTWAVE OR UPPER LOW ROTATES INTO THE EASTERN TROUGH
AND REACTIVATES A WARM FRONT OVER THE SOUTHEAST; POPS ARE NOW LIKELY
FOR SUNDAY. THE 00Z GFS AND ECMWF ACTUALLY SEEM TO OCCLUDE THE LOW
TO OUR WEST BY SUNDAY, WHEREAS THE CANADIAN GDPS MAINTAINS AN OPEN
WAVE, WHICH IS MORE SIMILAR TO EARLIER SOLUTIONS. THUS CONFIDENCE
AND POPS DECREASE MONDAY GIVEN THE SPREAD IN THE SPEED OF THE LOW
PRESSURE SYSTEM. TEMPERATURES DO REMAIN MILD, LIKELY AT LEAST A
LITTLE BELOW NORMAL.
AVIATION /07Z TUESDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: CIRRUS DEBRIS FROM DECAYING CONVECTION
UPSTREAM SHOULD INHIBIT RADIATION AND KEEP FOG AT BAY AT THE TAF
TERMINALS THIS MORNING; SOME RURAL/VALLEY LOCATIONS HAVE ALREADY
EXPERIENCED BRIEF RESTRICTIONS DUE TO FOG BUT THAT SHOULD BECOME
MORE ISOLATED AS THE HIGHER CLOUDS MOVE IN. SOME LOW VFR STRATUS
ALSO IS FORMING IN SOME LOCATIONS IN THE PRESENT WARM ADVECTION
REGIME AND THAT SHOULD HAVE THE SAME EFFECT. WINDS WILL BE LIGHT/VRB
THRU DAYBREAK BUT WILL PICK UP FROM THE SW 13-16Z WITH DIURNAL
MIXING (EXC. NW AT KAVL) AND GUSTS OF 20 KT ARE EXPECTED TO BE
COMMON AROUND THE AREA BY MIDDAY. A COLD FRONT WILL APPROACH FROM
THE NORTH THROUGH THE MORNING AND CONDITIONS ARE FAVORABLE FOR
STORMS TO FORM TO OUR NORTH AND WEST DURING THE MORNING. IT IS
POSSIBLE ANOTHER ROUND OF CIRRUS DEBRIS FROM SAID ACTIVITY WILL
ADVECT OVER THE TERMINALS LATE MORNING TO MIDDAY, INHIBITING THE
DEVELOPMENT OF STORMS IN THE AFTERNOON OR EVENING. INCLUDED VCSH
AND AN UPTICK IN CLOUD COVER DURING THE MORNING FOR THE DEBRIS
EFFECTS DURING THE MORNING. IN TURN, CONFIDENCE REMAINS RELATIVELY
LOW ON THE POTENTIAL FOR AFTERNOON AND EARLY EVENING STORMS, SO
PROB30S ARE STILL INCLUDED AT THAT TIME; MAY NOT HAVE CONFIDENCE
TO GO TEMPO UNTIL 12Z OR LATER AMDS. IF THE MORNING CLOUDS DON'T
INHIBIT ACTIVITY, IT APPEARS STORMS MAY FIRE EARLIER THAN USUAL,
SO THE PROB30S HAVE BEEN SHIFTED A BIT EARLIER THAN ON THE PREVIOUS
SET OF TAFS. ENVIRONMENTAL FACTORS SUGGEST IF THOSE TSRA DO FORM,
THEY WILL EASILY PRODUCE STRONG OUTFLOW WINDS AND TORRENTIAL
DOWNPOURS, AND POSE A THREAT OF LOCALIZED DAMAGING WINDS AND
GREATER THAN NORMAL HAIL POTENTIAL THAN MOST STORMS IN THIS AREA
THIS TIME OF YEAR. THE PROB30S NOW FEATURE VRB GUSTS TO 30 KT AND
IFR VSBY. ACTIVITY SHOULD SHIFT OUT OF THE REGION THIS EVENING
AS THE FRONT PASSES, AND WINDS SHIFT TO NW AT ALL SITES BEHIND
THE FRONT. A FEW SHRA COULD DEVELOP NEAR KAVL OVERNIGHT DUE TO
UPSLOPE FLOW INTO THE MTNS. POST-FRONTAL DRYING COULD INHIBIT FOG
FORMATION TONIGHT BUT CAN'T RULE OUT SOME SHALLOW FOG AFTER 06Z
ESPECIALLY WHERE HEAVY RAIN FALLS TODAY.
OUTLOOK: DRY AND MOSTLY VFR CONDITIONS RETURN WED THRU FRI, WITH
SHOWER AND THUNDERSTORM CHANCES AND THEIR ASSOCIATED RESTRICTIONS
RETURNING OVER THE WEEKEND. LOW STRATUS AND/OR FOG WILL BE POSSIBLE
EACH MORNING, MAINLY IN THE MTN VALLEYS.
GSP WATCHES/WARNINGS/ADVISORIES
GA...HEAT ADVISORY FROM NOON TODAY TO 8 PM EDT THIS EVENING FOR
GAZ018-026-028-029.
NC...NONE.
SC...NONE.
JCW
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