205
FXUS62 KGSP 311813
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
213 PM EDT SAT MAY 31 2025
SYNOPSIS
A FRONT STALLS OVER THE AREA THIS WEEKEND, KEEPING A CHANCE OF
ISOLATED TO SCATTERED SHOWERS AND STORMS, ESPECIALLY IN THE
MOUNTAINS. DRY HIGH PRESSURE BUILDS IN EARLY NEXT WEEK. TEMPERATURES
WILL BE SLIGHTLY BELOW NORMAL THROUGH THE WEEKEND, THEN RISE TO A
LITTLE ABOVE NORMAL NEXT WEEK AS A WARM AND HUMID AIR MASS RETURNS.
NEAR TERM /THROUGH TONIGHT/
AS OF 200 PM: WATER VAPOR IMAGERY SHOWS A DEEP TROUGH CENTERED OVER
THE EAST COAST, BRINGING A FAST NORTHWESTERLY MID TO UPPER LEVEL
FLOW OVER THE CWA. SMOKE FROM WILDFIRES IN THE CANADIAN PRAIRIE,
PICKED UP BY SAID FLOW, HAS BEEN ADVECTED OVER THE SOUTHEAST
US--VISIBLE ON SATELLITE. CURRENTLY THAT APPEARS TO BE ONLY AT HIGH
ALTITUDE, WITH NO SFC OBS REPORTING REDUCED VSBY. HRRR-SMOKE MODEL
SUGGESTS A MOUNTAIN WAVE THIS AFTERNOON MAY THE BRING SMOKE DOWNWARD
AND PRODUCE NOTICEABLE CONCENTRATIONS AT THE SURFACE, BUT CURRENTLY
NOT CONFIDENT ENOUGH TO REFLECT IN THE FCST. THE SMOKE DOES APPEAR
TO HAVE REDUCED INSOLATION ENOUGH TO KEEP OBS FROM WARMING AS MUCH
AS ALMOST ALL GUIDANCE WOULD HAVE SUGGESTED SO FAR TODAY, ALTHOUGH
GUSTY WINDS MAY HAVE PLAYED A ROLE IN THAT AS WELL. EXPECTING
SMOKE CONCENTRATION TO REMAIN AT OR ABOVE CURRENT VALUES THRU THE
AFTERNOON, LOWERED MAX TEMPS A BIT FROM THE PREVIOUS FCST.
THE AFOREMENTIONED FAST FLOW ALOFT IS RESPONSIBLE FOR THE GUSTY
WINDS SO FAR TODAY, AND ALSO WILL EXPOSE ANY CONVECTIVE UPDRAFTS
TO STRONG EFFECTIVE SHEAR. IT REMAINS QUESTIONABLE HOW DEEP THE
UPDRAFTS WILL BE ABLE TO GET. PROG SOUNDINGS FROM THE HRRR AND
HRW-FV3 DEPICT A CAPPING LAYER AROUND 600MB OVER MOST OF THE CWA,
WITH A MOIST LAYER AROUND 700MB BENEATH. THAT SHOULD EASILY RESULT
IN DECENT CUMULUS ABOVE THE PBL, BUT LIKELY NOT DEEP ENOUGH FOR
GOOD ICE NUCLEATION OR THUNDER. EVEN WITHOUT THUNDER, GIVEN THAT
A FEW SITES HAVE GUSTED TO 25-30 MPH WITH NOT SO MUCH AS A SHOWER
NEARBY, IF A SHOWER DOES DEVELOP THE DOWNDRAFT COULD PRODUCE
30-35 MPH WINDS. CAMS DO NOT DEPICT MUCH COVERAGE IN OUR CWA THIS
AFTERNOON AND EVENING. CAN'T COMPLETELY RULE OUT A SEVERE GUST OR
SMALL HAIL, BUT THINK THE SHOWERS PRODUCING BRISK SUBSEVERE GUSTS
ARE MUCH MORE LIKELY.
CONVECTION SHOULD DISSIPATE BY EARLY EVENING OUTSIDE OF THE
MOUNTAINS BUT WILL LINGER OVER THE NC MOUNTAINS BEFORE DISSIPATING
BY MIDNIGHT. THE GUSTY WINDS SHOULD FOLLOW A SIMILAR PATTERN. LOWS
WILL BE UP TO 5 DEGREES BELOW NORMAL.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
AS OF 255 AM EDT SATURDAY: BROAD CYCLONIC FLOW ALOFT REMAINS
OVERHEAD ON SUNDAY AS A SHORTWAVE ROUNDS THE BASE OF THE UPPER
TROUGH, SENDING A BACKDOOR FRONT FROM THE NORTH INTO THE CFWA. THE
PLACEMENT OF THE BOUNDARY WILL BE KEY TO WHAT DEVELOPS AS THIS COULD
BE A FOCUS FOR CONVECTIVE INITIATION. GENERALLY THE CAMS AND
DETERMINISTIC MODELS HAVE COME IN BETTER AGREEMENT AND DEVELOP
DIURNAL SHOWERS AND THUNDERSTORMS ACROSS THE AREA SUNDAY. DEEP LAYER
SHEAR OF 30-35 KTS AND 1000-1500 J/KG OF SBCAPE SUGGEST SOME
ORGANIZED CONVECTION SHOULD DEVELOP ALONG AND SOUTH OF THE BOUNDARY.
EXACT PLACEMENT WILL BE HARD TO PINPOINT UNTIL CLOSER TO THE EVENT,
BUT HIGHER POPS ARE CURRENTLY CONCENTRATED OVER MOST OF THE
MOUNTAINS AND IN THE PIEDMONT NEAR THE VICINITY OF THE NC/SC STATE
LINE. STEEPER MID-LEVEL LAPSE RATES, LOWER FREEZING LEVELS, AND
INVERTED-V PROFILES SUGGEST THAT LARGE HAIL AND DAMAGING WIND GUSTS
MAY DEVELOP WITH STRONGER STORMS. TEMPERATURES WILL BE A FEW TICKS
BELOW NORMAL FOR AFTERNOON HIGHS ON SUNDAY. THE FRONT IS EXPECTED TO
SAG SOUTH OF THE CFWA SUNDAY NIGHT AS A WEAK SURFACE HIGH PUSHES
INTO THE OH VALLEY AND DRIER AIR SETTLES IN. LINGERING CONVECTIVE
DEBRIS MAY OFFSET OTHERWISE GOOD DRY AIR ADVECTION AS OVERNIGHT LOWS
ARE FORECASTED TO STILL DIP A CATEGORY OR SO BELOW NORMAL FOR SUNDAY
NIGHT.
THERE ARE HINTS IN THE LATEST MODEL GUIDANCE OF THE BOUNDARY
STRUGGLING TO MAKE A FULL FROPA ACROSS THE SOUTHERN HALF OF THE CFWA
ON MONDAY. IN PARTICULAR, THE NAM DEVELOPS A COUPLE OF ISOLATED
SHOWERS AND THUNDERSTORMS ALONG AND SOUTH OF I-85, BUT NOT MUCH
SUPPORT ELSEWHERE, SO MENTIONABLE POPS ARE NOT CURRENTLY IN THE
FORECAST DUE TO LOW CONFIDENCE. OTHERWISE, MILD AND LOWER HUMID
CONDITIONS WILL BE IN STORE FOR MONDAY AS AFTERNOON HIGHS WILL BE A
CATEGORY OR LESS BELOW NORMAL. SURFACE HIGH ESTABLISHES MORE CONTROL
OF THE SENSIBLE WEATHER MONDAY NIGHT AS THE FRONT PUSHES WELL SOUTH
OF THE CFWA AND GOOD RADIATIONAL COOLING CONDITIONS DEVELOP. AS A
RESULT, OVERNIGHT LOWS SHOULD REMAIN A CATEGORY OR SO BELOW NORMAL.
LONG TERM /TUESDAY THROUGH FRIDAY/
AS OF 320 AM EDT SATURDAY: LONGWAVE UPPER RIDGING BEGINS TO REPLACE
THE CYCLONIC FLOW ALOFT BY TUESDAY AS WARMER THICKNESSES FILTER
IN AND SURFACE HIGH REMAINS IN CONTROL AT THE SURFACE. THE ECMWF
PROVED TO BE OUT TO LUNCH WITH THE 00Z FRIDAY RUN AS IS HAS BECOME
MUCH BETTER ALIGNED WITH THE OTHER DETERMINISTIC MODELS. EXPECT A
REBOUND IN TEMPERATURES AND HUMIDITY STARTING TUESDAY AND CONTINUE
TO RISE THROUGH THE REST OF THE WEEK. TEMPERATURES ARE FORECASTED
TO RUN A FEW TICKS ABOVE NORMAL FOR HIGHS AND LOWS TUESDAY AND
WEDNESDAY WITH DRY CONDITIONS.
THE UPPER RIDGE WILL SLIP EAST OF THE CFWA THURSDAY INTO FRIDAY,
WHICH IS A SLOWER IN PROGRESSION COMPARED TO PREVIOUS MODEL RUNS AS
THE FLOW ALOFT BECOMES MORE ZONAL. WITH THE SURFACE HIGH SHIFTING
OFFSHORE IN BERMUDA FASHION, LOW-LEVEL SOUTHWESTERLY FLOW WILL
INCREASE AHEAD OF A COLD FRONT TO THE WEST AND SUMMERTIME CONDITIONS
RETURN IN A BIG WAY FOR THE SECOND HALF OF NEXT WEEK. EXPECT
TEMPERATURES TO RISE A CATEGORY OR SO ABOVE NORMAL BY THURSDAY
AND LAST THROUGH NEXT WEEKEND, WITH A SLIGHT UPTICK IN DIURNAL
SHOWERS AND THUNDERSTORMS, ESPECIALLY IN THE MOUNTAINS.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
AT KCLT AND ELSEWHERE: VFR. CU FIELD THIS AFTERNOON WITH BASES
MOSTLY 035-050 OVER THE MOUNTAINS (KAVL) AND 060-080 OVER THE
OTHER SITES. WILDFIRE SMOKE AT HIGH ALTITUDE MAY FORM AN EFFECTIVE
BKN250 CIG OTHERWISE; SOME VSBY REDUCTION IS POSSIBLE AS A RESULT
OF THE SMOKE LATER THIS AFTN/EVENING BUT MOST LIKELY WILL REMAIN
P6SM. GUSTS OF 20-25 KT LIKELY AT ALL SITES THIS AFTN, HIGHER
AT TIMES AT KAVL. ISOLATED TO SCATTERED SHRA MAY DEVELOP NEAR
THE NC SITES THRU MID-EVENING, AND COULD EASILY PRODUCE 30-35 KT
GUSTS. CHANCE TOO SMALL TO MENTION. MAINLY WSW WINDS EARLY IN THE
PERIOD, FAVORING WNW BY AROUND 21Z. GUSTS MAY BRING WIND TO WNW
BRIEFLY EARLIER. CU FIELD AND ANY SHRA DIMINISH LATE EVENING IN
THE PIEDMONT; SOME SHRA COULD DEVELOP NEAR THE TN/NC BORDER LATER
INTO THE NIGHT. WINDS WILL TURN SW'LY AGAIN AFTER DIURNAL MIXING
BEGINS SUN. BETTER OVERALL CHANCE FOR SHRA/TSRA AFTER 18Z SUN,
PROMPTING PROB30 TSRA AT KCLT.
OUTLOOK: DRY HIGH PRESSURE AND VFR CONDITIONS MONDAY THROUGH
WEDNESDAY.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...CAC
NEAR TERM...RWH/WIMBERLEY
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...WIMBERLEY
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