570
FXUS62 KGSP 181751
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1251 PM EST WED DEC 18 2024
SYNOPSIS
MUCH COOLER CONDITIONS ARE EXPECTED TO FILTER INTO OUR REGION
LATE IN THE WEEK. A NORTHWEST FLOW SNOW EVENT WILL PRODUCE LIGHT
SNOW ALONG THE TENNESSEE BORDER AREAS FROM LATE FRIDAY THROUGH
SATURDAY MORNING. THE COLDEST DAYS ARE EXPECTED TO BE SUNDAY AND
MONDAY THEN A LITTLE WARMER FOR CHRISTMAS.
NEAR TERM /THROUGH TONIGHT/
FOR THE NOON UPDATE: ALLOWED THE SPS FOR FOG TO EXPIRE. AS EXPECTED,
SITES THAT CLEARED OUT ARE WARMING A LITTLE MORE THAN FCST, WHILE
AREAS OF LOW CLOUDS SPREADING IN FROM THE SOUTH ARE LIMITING WARMING
THERE. MINOR TWEAKS WERE MADE TO THE SKY GRIDS TO REFLECT LATEST
TRENDS. A FEW SHOWERS MAY DEVELOP NEAR THE DIFFERENTIAL HEATING
ON THE EDGE OF THE LOW CLOUD DECK ACROSS THE LOWER PIEDMONT. POPS
LOOK GOOD FOR THE CONVECTION APPROACHING FROM THE WEST, WHICH WILL
STRUGGLE TO CROSS THE MOUNTAINS THIS AFTN INTO THIS EVENING.
OTHERWISE, AFTER THE FOG DISSIPATES, TEMPERATURES SHOULD WARM
NICELY INTO THE UPPER 60S TO NEAR 70 ACROSS THE PIEDMONT AND
MOUNTAIN VALLEYS. DEWPOINTS WILL REMAIN IN THE MID TO UPPER 50S IN
MOST AREAS. AN INVERSION WILL PERSIST, AND SOME PATCHY LOW CLOUD
COVER MAY REMAIN INTO AFTERNOON BENEATH IT. AN UPPER SHORTWAVE WILL
TRACK EAST ACROSS THE LOWER OH/TN VALLEYS TODAY. MCS NOW NEAR THE
MS RIVER WILL WEAKEN DIURNALLY, ALTHOUGH THE CAMS TAKE IT ALMOST
TO THE NC BORDER. REMNANT SHOWERS HOWEVER ARE LIKELY TO REACH THAT
AREA BY 4-5 PM. EAST OF THE MOUNTAINS, A DRY LAYER ALMOST LIKE AN
EML WILL PERSIST ABOVE THE INVERSION. VARIOUS MODELS DEPICT SMALL
BUT RESPECTABLE SBCAPE ON PLAN VIEWS, BUT THE EML-LIKE FEATURE MOST
LIKELY WILL INHIBIT DEEP CONVECTION MOST OF THE DAY, AND UPGLIDE
BENEATH THE INVERSION APPEARS TOO WEAK TO EXPECT MUCH CHANCE OF
POP FROM THAT ALONE. HEIGHT FALLS WITH THE SHORTWAVE, HOWEVER,
REFLECT COOLING MID-LEVELS, AND CONVECTION LOOKS SOMEWHAT PLAUSIBLE
IN OUR SW CWA BY MID-AFTERNOON, WITH POPS INCREASING TO CHANCE
RANGE THERE ACCORDINGLY. THERE LIKELY WILL BE A SHARP INSTABILITY
GRADIENT NEAR OUR SE BORDER OR PERHAPS IN THE MIDLANDS--CAMS
ARE SPLIT AS TO WHERE THIS DEVELOPS. SAID GRADIENT ALSO MAY BE A
FOCUS FOR CONVECTION. HENCE SMALL CHANCE POPS ALSO CREEP IN FROM
THE SOUTH. WITH SO LITTLE GUIDANCE SUPPORT FOR PRECIP UNDER THE
INVERSION, CONSIDERED KEEPING THE NC PIEDMONT/FOOTHILLS DRY THRU
THE DAYTIME PERIOD, BUT GIVEN APPROACHING SHORTWAVE AND PREVIOUS
FCST CONTINUITY, ALLOWED A SLIGHT-CHANCE MENTION THERE LATE IN THE
DAY. SMALL THUNDER CHANCES ARE INCLUDED IN THE SOUTH AND FAR WEST
EDGES OF THE CWA; EFFECTIVE SHEAR OF 30 KT COULD ALLOW SOME MORE
VIGOROUS STORMS ALTHOUGH PROFILES ARE UNIDIRECTIONAL. EXCLUDING
THE EXCITABLE HRW-FV3, CAMS REALLY ARE NOT ALL THAT IMPRESSED
WITH THE SETUP FOR CONVECTION IN OUR SOUTHERN CWA. THAT SAID,
IF A STORM FORMS, IT WOULD NOT BE ALL THAT SURPRISING IF IT POSED
A VERY SMALL RISK OF DAMAGING WIND. PARTICULARLY WITH RELATIVELY
SMALL POP OVERALL, THE LACK OF AN SPC RISK AREA APPEARS APPROPRIATE.
LAPSE RATES IMPROVE IN OUR EAST AS THE SHORTWAVE ENTERS, SO THE
BEST OVERALL CHANCE FOR THE I-77 CORRIDOR IS AFTER 00Z, BUT STILL
ONLY AROUND 40%. COLD FRONT WILL SWEEP ACROSS THE MOUNTAINS THIS
EVENING AND POPS BEGIN TO DECLINE AFTER SUNSET, ALTHOUGH AS WINDS
TURN NORTHEASTERLY MOST GUIDANCE CONTINUES TO DEPICT CLOUD COVER,
ALBEIT MOST LIKELY WITHOUT APPRECIABLE FOG. ANY SHOWERS SHOULD
END BY MIDNIGHT, BEFORE TEMPS COOL ENOUGH IN THE TN BORDER AREA
TO BE CONCERNED FOR A CHANGE TO SNOW. MINS DIP TO AROUND FREEZING
IN THE HIGH ELEVATIONS AND GENERALLY IN LOWER 40S IN THE VALLEYS,
AND MID 40S FOR THE PIEDMONT.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
AS OF 200 AM EST WEDNESDAY: IN BETWEEN TWO SHORTWAVES WITH THE
NEAR-TERM TROUGH SLIPPING EAST OF THE CFWA AND A POTENT SHORTWAVE
DIGGING INTO THE NORTH-CENTRAL CONUS WITH A SURFACE LOW FOLLOWING
UNDERNEATH WILL LEAD TO A QUIET WEATHER PERIOD ON THURSDAY. WEAK
HIGH PRESSURE WILL SETTLE OVER THE REGION DURING THE DAY THURSDAY
WITH ONLY SUBTLE HEIGHT FALLS. AFTERNOON HIGHS ARE EXPECTED TO RUN
AT OR SLIGHTLY ABOVE NORMAL AS A RESULT. WINDS ATOP THE BOUNDARY
LAYER AND ALOFT WILL VEER MORE SOUTHWESTERLY THURSDAY NIGHT, WHILE
A NOTICEABLE DRY SLOT IS EVIDENT IN THE MID-LEVELS, CREATING A
LOW-LEVEL INVERSION LAYER. WITH A SLIGHT UPTICK IN 850MB WINDS
(15-20 KTS) OUT OF THE SOUTHWEST, LOW-LEVEL MOISTURE WILL BECOME
TRAPPED UNDERNEATH THE INVERSION AND MAY CREATE A LOW STRATUS
DECK OVERNIGHT THURSDAY. IN THIS CASE, OVERNIGHT LOWS THURSDAY
WILL RUN A FEW DEGREES ABOVE NORMAL, ESPECIALLY IF THE BOUNDARY
LAYER STRUGGLES TO FULLY DECOUPLE.
THE AFOREMENTIONED SHORTWAVE WILL SWING ACROSS THE MIDWEST AND OH
VALLEY THURSDAY AND SET UP SHOP OVER THE NORTHEAST AND MID-ATLANTIC
BY FRIDAY. THE ASSOCIATED SURFACE LOW WILL EJECT IN CLIPPER FASHION
NORTH OF THE CFWA. HOWEVER, ON THE BACKSIDE OF THE LOW, LOW-LEVEL
NORTHWEST FLOW FILTERS IN FRIDAY AFTERNOON/EVENING AS A VORT MAX
ROUNDS THE BASE OF THE SHORTWAVE AND CRASHES INTO THE CFWA. RECENT
MODEL GUIDANCE PRODUCES SLIGHTLY BETTER SATURATION IN LOW-LEVEL
PROFILES AND SUGGESTS THAT THE PRECIPITATION WILL BE COLD ENOUGH
FOR WINTRY P-TYPES, WHILE THE AVAILABLE MOISTURE SHOULD BE ABLE TO
TAP INTO THE DENDRITIC GROWTH ZONE. EXPECT A PERIOD OF NORTHWEST
FLOW SNOW ALONG THE NC/TN BORDER FRIDAY AFTERNOON THROUGH SATURDAY
MORNING. THE POSITION OF THE VORT MAX COULD FAVOR A FEW NORTHWEST
FLOW SNOW SHOWERS BREAKING CONTAINMENT FURTHER EAST INTO THE NORTH
CAROLINA MOUNTAINS, POTENTIALLY IN THE PARTS OF THE MAJOR MOUNTAIN
VALLEYS. A SECOND AREA OF LIGHT PRECIP IS NOW BEING PICKED UP BY THE
LATEST MODEL GUIDANCE ACROSS THE CLT METRO AND LOCATIONS ALONG AND
EAST OF I-77 FRIDAY AFTERNOON/EVENING IN ASSOCIATION WITH THE VORT
MAX AS IT TRAVERSES ACROSS THE CAROLINAS. PROFILES ARE TOO WARM
FOR WINTRY P-TYPES AND A VERY DRY SUB-CLOUD LAYER SUGGESTS THAT
ANY PRECIP THAT FALLS WILL HAVE TO INDUCE EVAPORATIONAL COOLING
BEFORE REACHING THE SURFACE. INTRODUCING SLIGHT CHANCE POPS IN
THE SPECIFIED LOCATIONS EAST OF THE MOUNTAINS FOR MEASURABLE
PRECIP, BUT THE DEVELOPMENT OF VIRGA WILL BE EVIDENT IF ANYTHING
ELSE. AFTERNOON HIGHS FRIDAY WILL BE NEAR-NORMAL FOR LOCATIONS
EAST OF THE MOUNTAINS AND MAJOR MOUNTAIN VALLEYS, WHILE INCREASING
CLOUD COVER AND CAA WILL KEEP TEMPERATURES IN THE 30S OVER THE
HIGHER ELEVATIONS.
ONGOING NORTHWEST FLOW SNOW ALONG THE NC/TN BORDER WILL GRADUALLY
DWINDLE IN COVERAGE OVERNIGHT FRIDAY AS THE VORT MAX SHIFTS
NORTHEAST OF THE CFWA. LINGERING LOW-LEVEL MOISTURE AND SCATTERED
VORT ENERGY ALOFT BEHIND THE MAIN VORT MAX WILL KEEP SNOW SHOWERS
GOING THROUGH AT LEAST DAYBREAK SATURDAY. SNOW AMOUNTS WILL VARY A
LOT, BUT CAN'T RULE OUT A COUPLE OF INCHES IN THE USUAL NORTHWEST
FACING SLOPES ALONG THE NC/TN BORDER, ESPECIALLY IN THE NORTHERN
MOUNTAINS. WITH SIGNIFICANT HEIGHT FALLS RESULTING IN COLDER AIR
ALOFT MOVING INTO THE AREA FRIDAY NIGHT, OVERNIGHT LOWS WILL DIP
A FEW TICKS BELOW-NORMAL FOR MOST LOCATIONS.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
AS OF 310 AM EST WEDNESDAY: ANY LINGERING NORTHWEST FLOW SNOW WILL
END SATURDAY MORNING FOLLOWED BY BREEZY CONDITIONS THANKS TO A TIGHT
PRESSURE GRADIENT WITH CAA PRESENT. BROAD CYCLONIC FLOW ALOFT AND
COLDER THICKNESSES WILL ALLOW TEMPERATURES TO DIP 5-10 DEGREES BELOW
NORMAL SATURDAY, WHILE A SHORTWAVE ROUNDS THE PERIPHERAL OF THE
BROAD UPPER TROUGHINESS IN PLACE TO HELP REINFORCE THE COLDER AIR
ALOFT ON SUNDAY, WHILE A LARGE AND STRONG SURFACE HIGH (~1040MB)
SLIPS INTO THE GREAT LAKES AND EVENTUALLY THE NORTHEASTERN CONUS
SUNDAY INTO SUNDAY NIGHT. THE LOCATION OF THE HIGH WILL FILTER IN A
CAD-LIKE CONFIGURATION INTO THE CFWA AND REMAIN IN PLACE GOING INTO
THE EARLY PART OF NEXT WEEK. A FLAT SHORTWAVE RIDGE BUILDS SHIFTS
OVER THE AREA MONDAY INTO TUESDAY AND THE HIGH SLIPS OFFSHORE BY
TUESDAY IN RESPONSE, AHEAD OF A CENTRAL CONUS UPPER TROUGH. AS A
RESULT, TEMPERATURES ARE LIKELY TO DROP 10-15 DEGREES BELOW NORMAL
SUNDAY AND MONDAY, WITH ONLY GRADUAL MODIFICATION BY TUESDAY. MUCH
COLDER CONDITIONS EXPECTED DURING THE MEDIUM RANGE, BUT THE SENSIBLE
WEATHER SHOULD REMAIN QUIET THROUGH THE FORECAST PERIOD.
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
AT KCLT AND ELSEWHERE: CONFIDENCE IS BELOW AVERAGE FOR THE CIGS
THIS AFTN INTO TONIGHT, AS A LIFR CLOUD DECK DRIFTS SLOWLY NORTH
FROM THE MIDLANDS TOWARD THE UPSTATE SITES AND KCLT. THE EDGE SEEMS
TO BE SLOWLY DOWN ON SATELLITE IMAGERY, BUT COULD BRIEFLY IMPACT
KAND. AN MVFR CU FIELD IS FORMING IN THE CLEAR AREAS OVER THE
TAF SITES, SO EXPECT THAT TO BE THE MAIN CIGS. A FEW SHOWERS MAY
DEVELOP, WITH CHANCES JUST HIGH ENOUGH TO WARRANT PROB30S AND/OR
TEMPOS. CONFIDENCE IS HIGHEST AT KAND AND KCLT, WHICH ARE CLOSE
TO A DIFFERENTIAL HEATING BOUNDARY ASSOCIATED WITH THE EDGE OF
THE LOW CLOUD DECK. MEANWHILE, A LINE OF WEAKENING CONVECTION IS
EXPECTED TO ENTER THE NC MOUNTAINS LATER THIS AFTN, AND CONTINUE
WEAKENING AS THE ACTIVITY TRIES TO CROSS THE MOUNTAINS TO THE
EAST. KAVL WILL LIKELY HAVE SOME SHRA AROUND THIS EVENING, SO WILL
CONTINUE A PROB30 THERE. SOME OF THE ACTIVITY MAY EVEN REACH KHKY,
BUT NOT EXPECTED TO IMPACT THE UPSTATE OR KCLT. A COLD FRONT WILL
PUSH THRU OVERNIGHT, TOGGLING WINDS FROM SW TO N/NE. GUIDANCE IS
MIXED ON HOW MUCH LOW STRATUS AND/OR FOG MAY BE ABLE TO FORM, AS
THE FRONT SLIPS THRU, SO WILL HANDLE WITH FEW/SCT LOW CLOUDS LATE
TONIGHT THRU THU MORNING (MAINLY THE UPSTATE). THERE IS EXPECTED
TO BE ENOUGH MIXING TO LIMIT FOG DEVELOPMENT, BUT SOME FOG CANNOT
BE RULED OUT IN THE PIEDMONT. AT KAVL, GUSTY N/NW WINDS EXPECTED
BEHIND THE FRONT, WITH POSSIBLY A BRIEF PERIOD OF MVFR CIGS. VFR
CONDITIONS WITH NE WINDS EXPECTED DURING THE DAY THU, BUT SOME
GUIDANCE SHOWS MVFR CLOUDS FORMING ACROSS PORTIONS OF THE UPSTATE
AND NC PIEDMONT TOWARD THE END OF THE 18Z TAF PERIOD.
OUTLOOK: BEHIND THE COLD FRONT, HIGH PRESSURE AND DRY CONDITIONS
LAST THROUGH THE WEEKEND, WITH THE EXCEPTION BEING A CHANCE FOR
SNOW ALONG THE TN BORDER FRI NIGHT INTO SAT WITH A REINFORCING
COLD FRONT. PERIODIC CIG RESTRICTIONS CAN'T BE RULED OUT UNTIL
THAT FRONT PASSES.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...DEO
NEAR TERM...ARK/WIMBERLEY
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...ARK
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