483
FXUS62 KGSP 172025
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
325 PM EST FRI JAN 17 2025
SYNOPSIS
LOW PRESSURE MOVING ACROSS THE REGION WILL PROVIDE WIDESPREAD
RAIN, WITH A WINTRY MIX ACROSS PORTIONS OF THE MOUNTAINS, LATE
TONIGHT AND EARLY SATURDAY MORNING, AND THEN A ROUND OF LIGHT
SNOW SHOWERS NEAR THE TENNESSEE BORDER LATER IN THE WEEKEND.
ARCTIC HIGH PRESSURE RETURNS MONDAY BRINGING BITTER COLD TO THE
REGION FOR NEXT WEEK. A STORM SYSTEM IS EXPECTED TO TRACK FROM
THE NORTHERN GULF OF MEXICO TO OFF THE SOUTHEAST COAST MIDWEEK.
NEAR TERM /THROUGH SATURDAY/
AS OF 222 PM FRIDAY: FORECAST STILL LOOKS GOOD THIS AFTERNOON, WITH
CLEAR SKY AND ONLY A FEW THIN CIRRUS MOVING IN FROM THE WEST. TEMPS
WERE CLOSE TO THE FCST AND GUIDANCE. A FEW SPOTS HAD DEWPOINT MIXING
OUT MORE THAN EXPECTED, BUT NOT ENOUGH TO MAKE WHOLESALE CHANGES
TO THE RH FORECAST. GOING FORWARD INTO THE EVENING, THE CLEAR SKY
SHOULD ALLOW TEMPS TO FALL QUICKLY EVEN AS LIGHT SOUTHERLY WIND
SUPPORTS SOME WEAK WARM ADVECTION, THOUGH MAINLY ALOFT.
THE SITUATION DETERIORATES LATE THIS EVENING. A DAMPENING SHORT
WAVE OVER THE SRN PLAINS THIS AFTERNOON WILL MOVE EAST ACROSS
THE OZARKS AND MID-MS VALLEY REGION TONIGHT. AS THIS HAPPENS,
UPPER DIVERGENCE IN THE LEFT EXIT REGION OF A JET STREAK MOVING
OVER THE NRN GULF COAST WILL SPREAD OVER FROM THE WEST AS DPVA
MOVES IN AT MID-LEVELS, ALONG WITH MOISTENING ISENTROPIC UPGLIDE
FROM MID-LEVELS DOWN TO LOW-LEVELS THROUGH THE EARLY MORNING
HOURS. THE COMBINATION OF FORCING AND MOISTURE SHOULD ALLOW
LIGHT PRECIP TO DEVELOP FROM WEST TO EAST BETWEEN MIDNIGHT AND
DAYBREAK OVER THE WESTERN HALF OF THE FORECAST AREA, THEN THROUGH
THE MID/LATE MORNING OVER THE REST OF THE WESTERN PIEDMONT. THE
PRECIP WILL HAVE TO FIGHT ITS WAY DOWN TO THE SURFACE AS IT WILL
BE DEVELOPING INTO A DRY SUB-CLOUD AIR MASS. AS THIS HAPPENS,
WET-BULB EFFECTS WILL COOL THE REMNANT SUBSIDENCE INVERSION
LAYER ACROSS THE REGION AND RE-ORIENT THE ATMOSPHERIC COLUMN
TO BE ESSENTIALLY ISOTHERMAL ABOVE THE SFC UP TO ABOUT 8K FEET,
AFTER WHICH THE TEMP DROPS OFF AS EXPECTED. WHAT THIS MEANS IS
WE ARE LOOKING AT AN ELEVATION-DEPENDENT RAIN V. SNOW SCENARIO,
APART FROM THE USUAL POSSIBLE BRIEF MIX WITH SLEET AT ONSET. THE
FORECAST TEMP/DEWPT WILL BE IMPORTANT AND WILL BE THE MAIN DRIVER
OF WHAT REACHES THE GROUND. THE TREND IN THE GUIDANCE WAS TOWARD
SLIGHTLY HIGHER TEMPS AND DEWPTS, MEANING HIGHER WET BULB TEMPS,
AND MORE OF A LIMIT TO THE EXTENT OF THE SNOW. TEMPS SHOULD STOP
FALLING AS THE CLOUDS THICKEN, AND SHOULD ACTUALLY START TO RISE
TOWARD DAYBREAK. SNOW LEVELS WILL MOST LIKELY BE AROUND 3K-4K FT
MSL. FORTUNATELY, THE QPF IS RELATIVELY LIGHT, SO THAT LIMITS THE
SNOW ACCUM TO 1-2 INCHES AT THE HIGHEST ELEVATIONS, AND LIMITS THE
POTENTIAL FOR GETTING TO ADVISORY CRITERIA IN MOST PLACES OUTSIDE
OF THE SMOKIES, BALSAMS, AND NANTAHALA MTS. OUTSIDE THE MTNS, THIS
SHOULD ALLOW FOR A BRIEF MIX OF RAIN/SNOW AT THE ONSET ALONG/N OF
I-40, BUT A CHANGEOVER EARLY IN THE DAY. NO ADVISORY IS PLANNED
FOR THIS. AS TEMPS WARM, PRECIP WILL CHANGEOVER TO ALL RAIN IN THE
MORNING EVEN AT THE HIGH ELEVATIONS. THE BETTER UPPER DIVERGENCE
AND DPVA WILL MOVE OFF LATE IN THE MORNING, TAKING THE HIGH PRECIP
PROBS WITH IT. HOWEVER, SOME WEAK FORCING WILL REMAIN ALONG/AHEAD
OF THE COLD FRONT AS IT STALLS BRIEFLY OVER THE MOUNTAINS. THAT
SHOULD KEEP SOME LOW PRECIP PROBS INTO THE AFTERNOON, BUT MOST
PLACES WILL SEE SOMETHING OF A LULL IN THE MID/LATE AFTERNOON, EVEN
AS THE DAY ENDS UP CLOUDY AND DAMP, WITH TEMPS JUST BELOW NORMAL.
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/
AS OF 3:19 PM EST FRIDAY...AN ACTIVE SHORT-TERM IS IN STORE WITH THE
APPROACH OF AN ARCTIC FRONT. THIS BOUNDARY WILL LIKELY BE SITUATED
NEAR THE TN-NC BORDER SATURDAY EVENING, BUT THE REAL COLD ARCTIC AIR
WILL LAG UPSTREAM OVER THE MIDWEST. A WAVE OF LOW PRESSURE OVER THE
GULF STATES IS EXPECTED TO TRACK NORTHEASTWARD ALONG THE BOUNDARY,
PASSING DIRECTLY THROUGH THE AREA LATE SATURDAY NIGHT INTO SUNDAY
MORNING. THE FRONT WILL TEMPORARILY STALL SATURDAY NIGHT WHEN THE
FLOW BACKS OUT OF THE SOUTH AHEAD OF THE LOW. PRECIPITATION MAY
DEVELOP ALONG AND EAST OF THE LOW TRACK IN THE EASTERN PIEDMONT
REGION, BUT THE FORCING IS SHALLOW, SO AMOUNTS WILL BE LIGHT.
THERMAL PROFILES SUPPORT ONE PTYPE IN THE PIEDMONT REGION - RAIN.
ANOTHER AREA OF LIGHT PRECIPITATION IS FAVORED TO DEVELOP ACROSS THE
MOUNTAINS AS THE BOUNDARY-LAYER FLOW SHIFTS FROM THE NORTHWEST,
PRODUCING OROGRAPHIC LIFT. THERE IS A RISK FOR A LIGHT GLAZE OF
FREEZING RAIN IN THE MOUNTAINS AT ELEVATIONS ABOVE 3500 FT WHERE
TEMPERATURES HOVER IN THE UPPER 20S AND LOWER 30S. THE HREF SHOWS 50-
60 PERCENT PROBABILITIES OF AT LEAST 0.01" OF ICE ACCRETION.
NORTHWEST WINDS ON THE BACKSIDE OF THE SURFACE LOW WILL ALLOW THE
ARCTIC FRONT TO SURGE SOUTHEASTWARD ACROSS THE AREA ON SUNDAY. THIS
WILL BE ACCOMPANIED BY A CHANGEOVER TO SNOW SHOWERS FROM WEST
TO EAST ACROSS THE MOUNTAINS DURING THE MID TO LATE MORNING.
THERE IS A POSSIBILITY THAT SOME CONVECTIVE SNOW SHOWERS MAKE IT
PASS THE MOUNTAINS AND INTO THE NC FOOTHILLS OR EVEN PIEDMONT
REGION AS THE FRONT SWEEPS EASTWARD DURING THE AFTERNOON AND
EARLY EVENING. SNOW ACCUMULATIONS OF 1-2" ARE FORECAST IN THE
CENTRAL AND NORTHERN MOUNTAINS NEAR THE TN-NC BORDER.
A TIGHT PRESSURE GRADIENT AS THE ARCTIC HIGH BUILDS IN WILL YIELD
GUSTY WINDS. THE HIGHEST WINDS ARE EXPECTED IN THE WESTERN NC
MOUNTAINS WHERE THE PROBABILITY OF GUSTS IN EXCESS OF 45 MPH (WIND
ADVISORY CRITERIA) RANGE BETWEEN 30-60 PERCENT LATE SUNDAY NIGHT-
MONDAY MORNING. STRONG COLD AIR ADVECTION WILL YIELD A SHARP DROP IN
TEMPERATURES BEHIND THE ARCTIC FRONT ON SUNDAY. THAT PATTERN WILL
CONTINUE INTO SUNDAY NIGHT-MONDAY MORNING, MARKING THE ARRIVAL OF
THE COLDEST AIRMASS OF THE WINTER THUS FAR. THE COMBINATION OF THE
COLD AIR AND BRISK WIND WILL YIELD FRIGID WIND CHILLS. LREF
PROBABILITIES OF COLD WEATHER ADVISORY CRITERIA BY EARLY MONDAY
MORNING ARE 10-20% IN THE LOWER/EASTERN PIEDMONT AND 20-30 PERCENT
IN NORTHERN PIEDMONT AND FOOTHILLS, AND SC/GA MOUNTAINS, INCREASING
TO 70-80% IN THE NC MOUNTAINS. LATER SHIFTS WILL CONSIDER THE NEED
FOR AN EXTREME COLD WARNING IN THE NORTHERN MOUNTAINS OF NC.
LONG TERM /TUESDAY THROUGH FRIDAY/
AS OF 3:19 PM EST FRIDAY...THE ARCTIC AIRMASS WILL BUILD OVERHEAD
MONDAY NIGHT AND TUESDAY. THIS WILL YIELD A VERY COLD START TO THE
PERIOD WITH TEMPERATURES 20 DEGREES BELOW NORMAL FOR WHAT IS
CLIMATOLOGICALLY THE COLDEST TIME OF THE YEAR THROUGH WEDNESDAY.
SUNNY SKIES WILL OFFER LITTLE CONSOLATION TO THE FRIGID CONDITIONS
WITH TEMPERATURES STRUGGLING TO RISE ABOVE FREEZING ACROSS MUCH
OF THE AREA. ADDITIONAL COLD WEATHER ADVISORIES MAY BE NEEDED
MONDAY NIGHT AND TUESDAY NIGHT WHERE LREF PROBABILITIES OF
REACHING CRITERIA RANGE BETWEEN 20-40% IN THE EASTERN PIEDMONT,
INCREASING TO 40-60 PERCENT IN THE CHARLOTTE METRO, AND 50-70%
IN THE NORTHERN MOUNTAINS.
AN AREA OF LOW PRESSURE IS EXPECTED TO ORGANIZE ON THE SOUTHWESTERN
PERIPHERY OF THE ARCTIC FRONT OVER THE NORTHERN GULF OF MEXICO LATE
MONDAY-TUESDAY. MODELS CONTINUE TO CONVERGE TOWARD THE LOW TAKING A
NORTHEAST TRACK EITHER JUST OFF THE SE US COAST (MOST LIKELY OVER
THE GULF STREAM) MIDWEEK. WHILE THERMAL PROFILES WILL DEFINITELY
SUPPORT ALL SNOW, THE HEAVIEST PRECIPITATION, AND POSSIBLY ALL THE
PRECIPITATION, WILL LIKELY STAY EAST OF THE AREA AND CLOSER TO THE
COAST. PROBABILITIES FROM THE NBM FOR AT LEAST A DUSTING OF SNOW ARE
AROUND 30-40 PERCENT IN OUR FAR EASTERN ZONES, WHICH COULD WITH COLD
ENOUGH GROUND TEMPERATURES, COULD CAUSE ISSUES IF IT FALLS DURING
THE TUESDAY EVENING RUSH.
ANOTHER SECOND WAVE OF LOW PRESSURE MAY DEVELOP ALONG THE OLD
ARCTIC BOUNDARY BY THE END OF NEXT WEEK. IT IS STILL TOO EARLY
TO NAIL DOWN SPECIFIC BUT EARLY INDICATIONS FAVOR A WINTRY MIX
CHANGING TO RAIN.
AVIATION /21Z FRIDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE: VFR LIKELY AT ALL TERMINALS WITH A LIGHT
SE TO S WIND UNTIL DAYBREAK SATURDAY, BUT THE ARRIVAL OF LIGHT
PRECIP FROM WEST TO EAST IN THE 09Z TO 13Z TIME FRAME WILL BRING THE
CEILING DOWN TO MVFR AND PERHAPS IFR BEFORE THE BULK OF IT DEPARTS
IN THE LATE MORNING/EARLY AFTERNOON. THE PRECIP SHOULD BE IN THE
FORM OF A WET SNOW AT HIGH ELEVATIONS OF THE NC MOUNTAINS, BUT THE
VALLEYS SHOULD STAY MOSTLY LIQUID. THERE WILL BE THE OPPORTUNITY TO
MIX SOME LIGHT SNOW IN AT TIMES AT KAVL BEFORE DAYBREAK, THUS THE
TEMPO. WILL EMPLOY THE PROB30 TOWARD THE END OF THE PERIOD TO HANDLE
THE UNCERTAINTY SHOWN IN THE GUIDANCE WITH THE DEPARTURE TIME OF THE
LIGHT PRECIP AND THE LOWERING OF THE CEILING TO IFR. THE GUIDANCE
IS REALLY TRENDING TOWARD MAINTAINING A CEILING/VIS RESTRICTION
THROUGH SATURDAY AFTERNOON EAST OF THE MTNS, PERHAPS LIFR WITH THE
CEILING, AS THE COLD FRONT LINGERS OVER THE MTNS AND LOW PRESSURE
STARTS TO FORM TO THE LEE OF THE MTNS. WILL LIMIT THE CEILING TO
IFR FOR THE TIME BEING DUE TO UNCERTAINTY.
OUTLOOK: IFR CIGS EXPECTED TO LINGER INTO SAT NIGHT, POSSIBLY WITH
A PERIOD OF LIFR CEILING/VIS IN DENSE FOG. NW FLOW SNOW SHOWERS
POSSIBLE SATURDAY NIGHT THRU SUNDAY NIGHT NEAR THE NC/TN BORDER,
NW OF KAVL. A VERY COLD AND DRY AIRMASS WILL SETTLE INTO THE AREA
EARLY NEXT WEEK.
CLIMATE
RECORDS FOR 01-20
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 69 1906 24 2009 53 1954 -13 1985
1890
KCLT 71 1951 30 1983 53 1890 -2 1985
1929 1893
1927
KGSP 72 1933 30 1983 56 1922 1 1985
RECORDS FOR 01-21
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 72 1927 8 1985 59 1927 -16 1985
KCLT 73 1935 24 1985 58 1954 -5 1985
KGSP 73 1927 26 1985 59 1933 -4 1985
RECORDS FOR 01-22
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 73 1932 21 1960 59 1933 0 1970
KCLT 74 1937 29 1970 60 1906 5 1970
KGSP 72 1938 31 1970 58 1933 3 1893
1921
RECORDS FOR 01-23
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 73 1927 20 2005 54 1999 1 1936
1936
KCLT 75 1927 27 1970 59 1999 9 2003
KGSP 73 1974 30 1970 58 1999 5 1893
1927
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...JK
NEAR TERM...PM
SHORT TERM...JK
LONG TERM...JK
AVIATION...PM
CLIMATE...
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