Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 241420
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
920 AM EST TUE FEB 24 2015

.SYNOPSIS...
A WEAK AREA OF LOW PRESSURE MOVING FROM THE GULF STATES IN THE
MORNING THEN BE OUT OVER THE ATLANTIC BY THIS EVENING.  A
MOIST AND WINTRY LOW PRESSURE SYSTEM WILL TRACK ACROSS SOUTHERN
GEORGIA AND UP THE CAROLINA COAST WEDNESDAY NIGHT THROUGH THURSDAY
MORNING.  COLD CANADIAN HIGH PRESSURE BUILDS INTO THE AREA FOR
THE END OF THE WEEK...THEN A WARMING TREND STARTS THE MONTH OF
MARCH.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 915 AM...THE RADAR RETURNS ARE BEGINNING TO SUBSIDE ACRS THE
AREA...AS BEST FORCING FOR PRECIP CROSSES THE CWFA DURING THESE LATE
MORNING HOURS. THE FCST LOOKS ON TRACK...WITH POPS TAPERING OFF FROM
WEST TO EAST THRU THE REST OF THE MORNING HOURS. WILL LEAVE THE
WARNING AND ADVISORIES AS IS WITH THIS UPDATE. TEMPS/SKY/WIND LOOK
ON TRACK AS WELL.

AS OF 630 AM EST TUESDAY...LATEST RADAR ANALYSIS CONTINUES TO
INDICATE WIDESPREAD BANDING OF SNOWFALL ACROSS THE REGION WITH SOME
OF THESE BANDS BEING FAIRLY INTENSE...ALLOWING VISIBILITY TO FALL
TO LESS THAN 1 MILE AT TIMES.  SNOWFALL CONTINUES TO ACCUMULATE AS
WETBULB EFFECTS HAVE ALLOWED SURFACE TEMPS TO FALL TO BELOW FREEZING
LEVELS ACROSS THE VAST MAJORITY OF THE FCST AREA.  STILL EXPECTING
THE PREVIOUS SNOW TOTALS TO PREVAIL THUS NO SIG CHANGES MADE TO THE
FCST OR ANY PRODUCTS.

AS OF 300 AM EST TUESDAY...MODEST SNOWFALL UNDERWAY ACROSS THE
REGION THIS MORNING AS UPPER SHORT WAVE AND CONSEQUENT SURFACE WAVE
SLIDE THROUGH THE SOUTHERN APPS.  ALREADY RECEIVING REPORTS OF
SNOWFALL ACCUMS AROUND AN INCH ACROSS PORTIONS OF THE NC MOUNTAINS
THIS MORNING...WITH NICE SNOW BANDS STILL UPSTREAM PER KMRX RADAR.
THUS...AFTER BLENDING IN LATEST NAM/SREF QPF...ENDED UP WITH ENOUGH
SNOWFALL TO JUSTIFY UPGRADING TO A WARNING ALONG THE TN LINE.
THEREFORE...WILL CONTINUE WITH CURRENT WWY FURTHER EAST ACROSS THE
FOOTHILLS/PIEDMONT REGIONS ALL THE WHILE UPGRADING THE ABOVE
MENTIONED ZONES TO A WARNING.  SPEAKING OF FURTHER EAST ACROSS THE
PIEDMONT...LATEST HRRR/NAM INDICATES THE HEAVIEST BANDS OF SNOWFALL
SLIDING EAST INTO THE I77 CORRIDOR REGION AROUND RUSH HOUR...OR
PERHAPS SLIGHTLY THEREAFTER.  AS MENTIONED ABOVE...NOT ENOUGH QPF IN
THE GUIDANCE TO WARRANT ANY UPGRADES...BUT CERTAINLY THINK THAT
EARLY ADVISORY ISSUANCE WAS A GOOD CALL AS LATEST STORM TOTAL SNOW
FCST IS APPROX 1 INCH FOR THE CHARLOTTE METRO AREA.

OTHERWISE...EXPECTING PRECIP TO SLIDE EAST THROUGH LATE MORNING
GIVING WAY TO A DRY FCST ACROSS NORTHEAST GA...NC FOOTHILLS...AND
THE PIEDMONT REGIONS.  CLOUDY SKIES WILL PREVAIL THROUGH MUCH OF THE
DAY BEFORE SKIES SCT SLIGHTLY LATE.  FURTHER WEST...MODELS CONTINUE
TO INDICATE PROLONGED LIGHT SNOWFALL ALONG THE TN LINE THEREFORE
ALSO AIDING TO TOTALS...THUS SLIGHT/CHANCE POPS WILL REMAIN IN THE
FCST FOR THESE AREAS THROUGH MIDNIGHT.  TEMPERATURES THROUGH THE
NEAR TERM WILL REMAIN BELOW NORMAL AS WETBULB EFFECTS AND OVERCAST
SKIES YIELD HIGHS IN THE 20S ACROSS THE MTNS...LOWER/MID 30S OVER
THE REMAINDER OF THE FCST AREA.  AS FOR OVERNIGHT LOWS...EXPECTING
THE ENTIRE REGION TO FALL BELOW FREEZING THEREFORE SOME BLACK ICE
CONCERNS MIGHT ARISE AS ANY LINGERING WET ROADS REFREEZE...IF ONLY
MINIMAL DRYING OCCURS TODAY.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 330 AM TUESDAY...WE MIGHT HAVE AN EVEN MORE INTERESTING STORM
TO DEAL WITH AFTER WE ARE FINISHED WITH THIS MORNINGS EVENT. OUR
FOCUS SHIFTS TO THE NEXT SURFACE WAVE THAT DEVELOPS OVER THE NW GULF
OF MEXICO EARLY WEDNESDAY IN RESPONSE TO A STRONG WAVE MOVING EAST
ACROSS THE SRN PLAINS. CONFIDENCE CONTINUES TO SLOWLY INCREASE AS TO
THE EXPECTED EVOLUTION OF THIS SYSTEM AS AT CROSSES THE DEEP SOUTH
THROUGH WEDNESDAY NIGHT AND MOVES OFFSHORE THURSDAY MORNING...AND IS
NOW ABOVE AVERAGE FOR WHAT IT HAS BEEN SO FAR THIS SEASON. THE
MODELS ARE IN GOOD AGREEMENT WITH BRINGING A RAPID INCREASE IN
FORCING ACROSS NE GEORGIA LATE WEDNESDAY AND THEN ACROSS THE WRN
CAROLINAS MAINLY ON WEDNESDAY EVENING. A COUPLED JET INTERACTION
SHOULD BRING EXCELLENT UPPER DIVERGENCE AS THE DAMPENING SHORT WAVE
MOVES OVERHEAD. LOW LEVEL ISENTROPIC UPGLIDE SHOULD ALSO KICK IN BY
AROUND 00Z THURSDAY. A CONSENSUS OF THE GUIDANCE BRINGS PRECIP NEWD
STEADILY LATE IN THE DAY. WILL FINE TUNE THE PRECIP PROBABILITY TO
GO WITH A CATEGORICAL TO LIKELY POP WITH A NW TO SE GRADIENT FOR
WEDNESDAY NIGHT...WITH PRECIP CHANCES DROPPING OFF EARLY THURSDAY
MORNING WITH THE PASSAGE OF THE LOW TO THE SOUTH AND THE EXIT OF THE
STRONGER FORCING AFTER 06Z. PARTIAL THICKNESS AND FCST SOUNDINGS
ONCE AGAIN SUGGEST PRECIP TYPES LOOK TO BE A RAIN VERSUS SNOW
SCENARIO...WITH SFC WET BULB TEMPS PLAYING A BIG PART. THINK THE
STRONG FORCING WILL RESULT IN SOME DYNAMIC COOLING THAT WILL HELP
KEEP PROFILES BELOW FREEZING SUCH THAT THE HEAVIER PRECIP WILL FALL
AS SNOW ACROSS ALL BUT MAYBE THE LOWER PIEDMONT AND LAKELANDS OF SC.
THE FCST LEANS MORE ON THE ENSEMBLE GUIDANCE IN ORDER TO DAMPEN SOME
OF THE RUN-TO-RUN VARIABILITY OF THE LOW TRACK AND NRN EXTENT OF THE
PRECIP SHIELD. THE FCST ALSO BORROWS HEAVILY FROM THE QPF GUIDANCE
ISSUED BY WPC...AND ONCE THAT IS CONVERTED TO SNOWFALL...WE HAVE A
FCST THAT SUGGESTS WE WILL REACH 12HR WARNING CRITERIA SNOWFALL
ACROSS ALMOST ALL THE FCST AREA. THE PLUME DIAGRAMS FROM THE 03Z
SREF ARE COMPELLING. ONCE AGAIN...THE MAJORITY OF THE SREF MEMBERS
HAVE WARNING CRITERIA SNOWFALL AT MOST SITES BY 06Z THURSDAY. THERE
ARE A FEW CAVEATS...WHICH IS TO BE EXPECTED GIVEN MOST EVENTS DO NOT
ALWAYS GO ACCORDING TO PLAN. THE FCST STILL ASSUMES THAT COLD AIR
WILL ARRIVE FROM THE N/NW AS THE PRECIP SPREADS UP FROM THE SW AS
THE BOUNDARY LAYER ALSO COOLS WEDNESDAY EVENING. IF THE COLD AIR IS
DELAYED...MORE OF THE PRECIP WILL FALL AS RAIN ALONG/S OF I-85. IF
THE TRACK OF THE LOW REMAINS TOO FAR S...THE MTNS AND I-40 CORRIDOR
WILL NOT GET SUFFICIENT PRECIP TO REACH WARNING CRITERIA. THERE WILL
PROBABLY BE A 50 MILE WIDE BAND WHERE SNOWFALL IS MAXIMIZED...
RUNNING WSW TO ENE ACROSS THE WESTERN CAROLINAS AND NE GEORGIA. ALL
THAT ASIDE... THINK THE BEST COURSE OF ACTION IS TO ISSUE A WINTER
STORM WATCH WITH THIS FCST PACKAGE...AS CONFIDENCE IS ABOVE 50 PCT
THAT WE WILL SEE SOMETHING IN THE NEIGHBORHOOD OF 3-4 INCHES OF SNOW
MAINLY WEDNESDAY EVENING. WILL OPT TO KEEP THE GOALPOSTS WIDE FOR
NOW...SO THE WATCH WILL BE ISSUED FOR THE ENTIRE FCST AREA FOR
WEDNESDAY NIGHT.

THE REST OF THE FCST IS LESS BUSY. THERE SHOULD BE SOME LINGERING
SNOW POTENTIAL ACROSS THE MTNS ON THURSDAY...BUT MODEL GUIDANCE ALSO
SUGGESTS SOME LINGERING SHOWERY PRECIP MAINLY ACROSS THE NC
FOOTHILLS AND WRN PIEDMONT INTO THURSDAY EVE. ANY NW FLOW POTENTIAL
ON THE TN BORDER SHOULD DIMINISH BY FRIDAY MORNING.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 250 AM MONDAY...NO CHANGES MADE TO THIS DISCUSSION AFTER
REVIEWING NEW GUIDANCE...SO LOOKS QUITE GOOD.

THE EARLY PART OF THE MEDIUM RANGE WILL FEATURE A CONTINUATION
OF UNSEASONABLY COOL TEMPERATURES...AS A BROAD LONG WAVE TROUGH
REMAINS CARVED OUT OVER THE EASTERN CONUS...WITH A HIGH LATITUDE
CONNECTION SUPPORTING MAINTENANCE OF A STRONG AND EXPANSIVE...
1040 MB SURFACE THAT WILL OOZE ITS WAY ACROSS THE EASTERN HALF
OF THE COUNTRY INTO THE EARLY WEEKEND. OTHER THAN SOME LINGERING
NW FLOW SNOW IN THE WAKE OF THE COASTAL CYCLONE THU NIGHT...
THE LATTER PART OF THE WORK-WEEK SHOULD BE DRY AND COLD...
WITH TEMPS 15-20 DEGREES BELOW CLIMO.

A PATTERN SHIFT IS THEN ANTICIPATED FOR THE WEEKEND...AS LARGE SCALE
HEIGHT FALLS OVERSPREAD THE WESTERN CONUS...ALLOWING A RIDGE TO
BEGIN BUILDING ALONG THE EAST COAST. AS THE BROAD/ZONALLY ORIENTED
SURFACE HIGH BUILDS INTO THE NORTHEAST AND MID-ATLANTIC OVER THE
WEEKEND...A COLD AIR DAMMING SCENARIO MAY BECOME ESTABLISHED ALONG
THE EASTERN SEABOARD...THUS TEMPS ARE LIKELY TO REMAIN BELOW CLIMO
THROUGH THE WEEKEND...DESPITE RISING HEIGHTS. CONSIDERING THE
ORIENTATION OF THE PARENT HIGH...MOISTURE ADVECTION OVER THE COOL
DOME WILL RESULT IN PLENTY OF CLOUDS AND PERHAPS SOME LIGHT PRECIP
ON SATURDAY. DEPENDING UPON HOW EARLY IN THE DAY ANY PRECIP
FALLS...SOME WINTRY WEATHER CANNOT BE RULED OUT...ESP ACROSS THE
MTNS AND I-40 CORRIDOR.

MEANWHILE...MOISTURE RETURN BEGINS IN EARNEST SAT NIGHT INTO
SUNDAY...AS CYCLOGENESIS TAKES PLACE ACROSS THE CENTRAL CONUS...
WITH RESULTANT WAA/UPGLIDE PRECIP POSSIBLE ACROSS OUR REGION. BY
THIS TIME...COLD AIR DAMMING SHOULD BE WEAKENING AS HEIGHTS CONTINUE
TO RISE. THUS PRIMARILY RAIN IS EXPECTED...WITH RAIN CHANCES
CONTINUING INTO MONDAY AS A COLD FRONT APPROACHES FROM THE TENN
VALLEY.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
AT KCLT...VFR/MVFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD AS
SURFACE WAVE AND ASSOCIATED SN CONTINUE TO MOVE ACROSS THE REGION
THIS MORNING.  INITIALIZED TAF WITH -SN UNDER IFR VISB THROUGH 14Z
BEFORE IMPROVING TO MVFR.  PREVAILED -SN THROUGH 16Z BEFORE ALL WX
MENTION IS REMOVED AS PRECIP SLIDES OUT OF THE REGION WITH MVFR CIGS
LINGERING THROUGH THE REMAINDER OF THE DAY.  SNOW TOTAL CONTINUE TO
LOOK LIGHT WITH UP TO AN INCH AT BEST FCST FOR THE AIRFIELD.  WINDS
WILL REMAIN LIGHT AND NE UNTIL EARLY AFTERNOON BEFORE VEERING
SOUTHERLY.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH MVFR/IFR PREVAILING
WITH -SN AT ALL SITES WITH THE EXCEPTION OF KHKY WHERE A TEMPO WAS
FAVORED FOR SUCH.  ACCUMULATIONS WILL VARY FROM WEST TO EAST...WITH
THE HIGHEST ACCUMULATIONS BEING ALONG THE HIGHER TERRAIN.
THUS...WOULD NOT BE SURPRISED TO SEE AN ADDITIONAL INCH AT KAVL ON
TOP OF WHAT HAS ALREADY FALLEN...WITH GENERALLY AN ADDITIONAL HALF
INCH TO AN INCH AT THE OTHER TAF SITES.  REMOVED ALL WX MENTION BY
THE 16-17Z TIMEFRAME AT ALL SITES WITH LINGERING CIG RESTRICTIONS
UNTIL LATE IN THE PERIOD.  WINDS THROUGH THE PERIOD WILL REMAIN
LIGHT/MODERATE AND VEER FROM NE TO SSW.

OUTLOOK...ANOTHER ROUND OF WINTRY WEATHER IS LOOKING EVER MORE
LIKELY ON WEDNESDAY EVENING LEADING TO POSSIBLE FLIGHT RESTRICTIONS
AT ALL SITES WITH SOME ACCUMULATING SNOWFALL. BEYOND THAT...LOW
LEVEL MOISTURE WILL LINGER THROUGH THE REMAINDER OF THE
WEEK...HOWEVER CONFIDENCE IN FLIGHT RESTRICTIONS REMAINS TOO LOW TO
MENTION AT THIS TIME.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR GAZ010-017-
     018-026-028-029.
     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH LATE
     WEDNESDAY NIGHT FOR GAZ010-017-018-026-028-029.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ035>037-
     053-056-057-062>065-068>072-082-501>510.
     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH LATE
     WEDNESDAY NIGHT FOR NCZ033-035>037-048>053-056>059-
     062>065-068>072-082-501>510.
     WINTER STORM WARNING UNTIL 4 PM EST THIS AFTERNOON FOR NCZ033-
     048>052-058-059.
SC...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR SCZ001>014-
     019.
     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH LATE
     WEDNESDAY NIGHT FOR SCZ001>014-019.

&&

$$
SYNOPSIS...DEO
NEAR TERM...ARK/CDG
SHORT TERM...PM
LONG TERM...DEO/JDL
AVIATION...CDG


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