Area Forecast Discussion
Issued by NWS Greer, SC

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536
FXUS62 KGSP 140024
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
724 PM EST SAT FEB 13 2016

.SYNOPSIS...
COLD ARCTIC HIGH PRESSURE WILL BUILD ACROSS THE REGION THROUGH
MONDAY...WHILE A MOIST STORM SYSTEM CROSSES FROM THE WEST LATE
SUNDAY INTO TUESDAY. A FAST MOVING UPPER LEVEL SYSTEM WILL REACH THE
MOUNTAINS LATE TUESDAY...BEFORE DRY AND SEASONAL HIGH PRESSURE
RETURNS AND REMAINS THROUGH THE END OF THE WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 720 PM...LATEST SATELLITE IMAGES INDICATE CLEAR SKY ACROSS THE
FOOTHILLS AND PIEDMONT...WITH INCREASING CIRRUS CLOUDS STREAMING SE
ACROSS THE MID MISSISSIPPI RIVER VALLEY. THE HIGH CLOUDS ARE
ASSOCIATED WITH ARCTIC HIGH PRESSURE PUSHING ACROSS THE GREAT PLAINS
AND MID WEST. AS THE HIGH APPROACHES...WINDS SHOULD VEER FROM THE NE
AND HIGH CLOUD COVER WILL INCREASE. BY SUNDAY AFTERNOON...THE CENTER
OF THE HIGH IS EXPECTED TO REACH THE NEW ENGLAND COAST...WITH
RIDGING SOUTHWARD.

AS OF 515 PM...I WILL UPDATE THE FORECAST TO REDUCE SKY COVER AND
POPS TO ZERO. THIS EVENING WILL BE CLEAR AND COLD...WITH FREEZING
TEMPERATURES DEVELOPING EAST OF THE MTNS SHORTLY AFTER SUNSET.

AT 230 PM SATURDAY...AN UPPER TROUGH ALONG THE EASTERN SEABOARD THIS
AFTERNOON WILL DEAMPLIFY AND PROGRESS OF THE COAST ON SUNDAY...WHILE
ANOTHER TROUGH STARTS TO AMPLIFY OVER THE MS RIVER VALLEY.
MEANWHILE...SURFACE HIGH PRESSURE WILL MOVE FROM THE UPPER MS RIVER
VALLEY TODAY...TO NY BY LATE SUNDAY. THE RESULT WILL BE A
REDUCTION THE PRESSURE GRADIENT OVER THE SOUTHERN APPALACHIANS
TONIGHT...AND THEN THE SETTING UP A WEDGE OF COLD AIR ALONG THE EAST
SLOPE OF THE APPALACHIANS ON SUNDAY.

MOISTURE WILL SPREAD NORTH OVER THE GULF STATES ON SUNDAY AHEAD OF A
SURFACE LOW CROSSING NORTHERN TX...LIFTED ISENTROPICALLY OVER A
FRONT IN THE LOWER MS RIVER VALLEY. GUIDANCE SHOWS THE EASTERN EDGE
OF THIS MOIST UPGLIDE REACHING THE SOUTHERN APPALACHIANS DURING THE
DAY ON SUNDAY. DEEP MOIST THERMAL PROFILES ICE NUCLEATION...AND COLD
SURFACE TEMPERATURES...WILL ALLOW SNOWFALL TO REACH THE GROUND...
ALBEIT WITH LIGHT ACCUMULATIONS TO BEGIN WITH.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 300 PM EST SATURDAY...WELL...THE SHORT TERM REMAINS A
MESS...SO NOT MUCH HAS CHANGED THERE. STILL QUITE A BIT OF
UNCERTAINTY BUT IT IS STARTING TO LOOK BETTER. WE HAVE BEEN
ADVERTISING THE SYNOPTIC SETUP FOR QUITE SOME TIME...AND OVERALL
NO REAL CHANGES THERE. WE ARE STARTING THE SHORT TERM VERY COLD AT
THE SURFACE WITH THE ARCTIC HIGH PRESSURE IN PLACE AND DEEP UPPER
TROUGH OVER THE EASTERN SEABOARD. SHORTWAVE DIVING OUT OF THE PLAINS
ON THE BACKSIDE OF THE TROUGH WILL HELP TO PUSH THE SURFACE HIGH
PRESSURE EAST...ALLOWING IT TO DAM DOWN THE EASTERN SEABOARD IN
A HYBRID CAD EVENT. ANOTHER SHORTWAVE COMING OUT OF THE ROCKIES
INTO THE CENTRAL AND SOUTHERN PLAINS WILL INCREASE THE AMPLITUDE
OF THE WAVE AND BRING MOISTURE UP OVER THE DEEP SOUTH AND INTO
THE TENNESSEE VALLEY. BIGGEST POINT OF UNCERTAINTY REMAINS IN THE
TRACK OF THE SURFACE LOW. OF THE OPERATIONAL MODELS...12Z ECWMF
REMAINS ON THE NORTHWEST SIDE /NORTHWEST OF THE APPALACHIANS/ AND
THEREBY THE WARMEST...NAM KEEPS THE SURFACE LOW ACROSS THE CENTRAL
CAROLINAS /AND THEREBY THE COLDEST/...WITH THE GFS IN BETWEEN. TO
KEEP A FAIRLY CONSISTENT FORECAST AND LINE UP WITH NEIGHBORS AND
PER NATIONAL GUIDANCE SUGGESTIONS...LEANED TOWARD THE MIDDLE OF
THE ROAD WITH THE GFS...BUT IT MUST BE STRESSED THAT ONCE WE START
GETTING A BETTER HANDLE ON THE TRACK OF THE LOW...ANY SMALL CHANGES
COULD RESULT IN LARGE CHANGES TO THE FORECAST.

SO WHAT WE HAVE IN STORE IS AN ALL BELOW-FREEZING COLUMN TO
BEGIN WITH AS MOISTURE OVERSPREADS THE AREA FROM THE WEST
SUNDAY NIGHT. SHOULD BEGIN AS ALL SNOW EVERYWHERE BUT SHOULD
SEE A CHANGEOVER FROM SOUTH TO NORTH TO SLEET AND THEN FREEZING
RAIN STARTING IN THE PREDAWN HOURS ON MONDAY AS WAA ALOFT BEGINS
TO KICK IN. WITH NEW GUIDANCE...BEST QPF IS NOW ON THE WESTERN
SLOPES OF THE APPALACHIANS AND WITH DEEP NEAR-FREEZING ISOTHERMAL
LAYER...EXPECT LOWER SNOW RATIOS /MORE LIKE 8:1/...LOWERING FURTHER
STILL AS SNOW MIXES WITH SLEET. AN INTRUSION OF DRY AIR BY MIDDAY
MONDAY WILL REALLY REDUCE THE QPF RATES ACROSS THE UPSTATE AND
PORTIONS OF THE NC PIEDMONT. THIS WILL BE COINCIDENT WITH THE WAA
BEGINNING IN EARNEST AT THE SURFACE AND THE SURFACE COLD DOME WILL
ERODE BETWEEN 00Z-06Z TUESDAY...SO EXPECT JUST ABOUT EVERYWHERE
TO SEE A CHANGEOVER TO RAIN AROUND THIS POINT. TOWARD DAYBREAK
TUESDAY...THE NORTHERN MOUNTAINS MAY HOVER AROUND FREEZING SO
HAVE ALLOWED FREEZING RAIN TO LINGER ACROSS THOSE AREAS THROUGH
ABOUT DAYBREAK...BUT THEN AS THE COLD FRONT APPROACHES WILL SEE
THE UPPER WARM NOSE BEGIN TO ERODE...INTRODUCING ICE NUCLEI BACK
INTO THE PICTURE...WITH THE SHORT TERM ENDING WITH A RETURN TO
SNOW ACROSS THE NORTHERN MOUNTAINS.

SO WITH ALL THIS...HIGHEST CONFIDENCE RIGHT NOW IS IN
POPS...FOLLOWED BY QPF...FOLLOWED BY HOURLY TEMPERATURES...FOLLOWED
BY PTYPE AND THEN LASTLY SNOW/ICE ACCUMS. HAVE STUCK VERY CLOSE
TO WPC GUIDANCE AND FOR SNOW AMOUNTS THE RESULT IS 4-5 INCHES
ACROSS THE NORTHERN MOUNTAINS...2-4 INCHES ACROSS THE SOUTHWEST
MOUNTAINS...1-3 INCHES ACROSS THE FOOTHILLS...WITH UP TO AN
INCH ACROSS THE NORTHWEST PIEDMONT. THE COMPLICATION WITH THE
SNOW AMOUNTS IS THAT ACROSS THE UPSTATE AND PORTIONS OF THE NC
PIEDMONT /CHARLOTTE AREA/...A GOOD CHUNK OF THAT WOULD ACTUALLY BE
SLEET. THIS COMPLICATES AREAL EXTENT OF ANY POSSIBLE WATCHES. AS
FOR FREEZING RAIN...BEST ACCRETION WILL BE ACROSS THE NORTHERN
TIER OF THE FORECAST AREA...WITH A TRACE TO LESS THAN 0.1 ELSEWHERE.

SINCE SUNDAY NIGHT IS NOW 3RD PERIOD...AND AFTER COLLABORATION
WITH SURROUNDING OFFICES...HAVE OPTED TO ISSUE A WATCH. WILL
TRY TO EXPLAIN THE PLACEMENT AS BEST AS POSSIBLE.  STARTED AREAS
NORTHWEST OF A LINE GENERALLY FROM FRANKLIN TO ASHEVILLE TO LENOIR
AT 00Z MONDAY TO LINE UP WITH HIGH CHANCE TO LIKELY POPS /ALL SNOW/
SPREADING ACROSS THE MOUNTAINS. SPREAD THE WATCH SOUTHEAST INTO THE
PIEDMONT...GENERALLY FROM CARNESVILLE GA TO GSP TO CHARLOTTE...AFTER
06Z MONDAY AS THE PRECIPITATION SPREADS SOUTHEAST. DROPPED
THE WATCH FOR ALL BUT THE NORTHERN MOUNTAINS AT 00Z TUESDAY AS
TEMPERATURES SHOULD BE ALL ABOVE FREEZING BY THEN...BUT LINGERED FOR
YANCEY/MITCHELL/AVERY THROUGH 12Z TUESDAY. NOW...GIVEN DIFFERENT 12-
AND 24-HR SNOW CRITERIA ACROSS THE FORECAST AREA...THE WATCH IS A
BIT OF A STRETCH ACROSS PORTIONS OF SW NC WHERE WE NEED 4 INCHES
IN 12 HOURS FOR A WARNING. ACROSS NE GA...UPSTATE SC...AND THE
WESTERN NC PIEDMONT...CONFIDENCE IN GENERAL IS PRETTY DARN LOW AND
REALLY ONLY BASED ON THE FACT THAT WE COULD POSSIBLY SEE ENOUGH
SLEET MONDAY MORNING...BEFORE IT MELTS...TO MAYBE REACH WARNING
CRITERIA /YES I USED POSSIBLY AND MAYBE IN ONE SENTENCE/. PROBABLY
MORE OF AN ADVISORY SITUATION BUT STILL ENOUGH UNCERTAINTY IN THE
SURFACE LOW TRACK THAT I FEEL OKAY WITH THE WATCH.

I AM SURE THAT I MISSED SOME METEOROLOGICAL DETAILS THAT WERE
INCORPORATED INTO THE GRIDS AND WATCH PHILOSOPHY BUT THIS IS LONG
ENOUGH AS IT IS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM EST SATURDAY...STILL THINK WE WILL HAVE A LULL OF SORTS
BETWEEN WHEN THE MAIN LOW PRESSURE CENTER EXITS AND WHEN THE
UPSTREAM CLIPPER-LIKE SYSTEM ARRIVES FROM THE WNW. THE ECMWF HAS A
FASTER ARRIVAL...ESSENTIALLY BY AROUND SUNSET TUESDAY...WHILE THE
GFS DOES NOT BRING THE WAVE IN UNTIL SOME TIME IN THE MID-EVENING.
WILL OPT TO TAPER THE PRECIP PROB BACK TO SLIGHT CHC ON THE TN
BORDER AT 00Z WEDNESDAY...BEFORE QUICKLY RAMPING IT BACK UP THRU
LATE EVENING. THE SHORT WAVE SHOULD PROVIDE SOME EXTRA FORCING...SO
A LIKELY POP IS WARRANTED BRIEFLY ON TUESDAY EVENING. AFTER THE
SHORT WAVE PASSES...MOISTURE BECOMES SHALLOW AND SLOWLY
DIMINISHES...SO THE PRECIP PROBABILITY TAPERS OFF TO A CHC FOR
WEDNESDAY. THINK THE GFS HAS THE BETTER HANDLE ON KEEPING THE PRECIP
CONTAINED TO THE UPSLOPE AREAS ON THE TN BORDER...SO LOCATIONS EAST
OF THE BLUE RIDGE REMAIN DRY. AS IT STANDS RIGHT NOW...IT LOOKS LIKE
A MARGINAL EVENT. THE AIR MASS IS NOT PARTICULARLY COLD. THE 850 MB
WINDS ARE MORE WESTERLY. BACKWARD TRAJECTORIES SHOW AN AIR STREAM
THAT DOES NOT CROSS THE GT LAKES. THE GROUND WILL PROBABLY BE
COVERED WITH SNOW UPSTREAM ACRS TN AND KY AS WELL. ALL THESE
LIMITING FACTORS WILL PROBABLY CONSPIRE TO KEEP SNOW AMTS BELOW
ADVISORY CRITERIA. THE UPPER PATTERN WILL BE PROGRESSIVE OUT IN THE
MEDIUM RANGE...SO THAT BY WEDNESDAY NIGHT...THE UPPER TROF WILL MOVE
OFFSHORE AND AN UPSTREAM RIDGE WILL START TO BUILD IN. THUS...A
WARMING TREND IS ANTICIPATED THROUGH LATE WEEK WITH THE UPPER RIDGE
AXIS MOVING OVERHEAD ON FRIDAY. TEMPS SHOULD CLIMB BACK TO NORMAL
LATE WED AND THU...AND THEN ABOVE NORMAL ON FRIDAY. THE PATTERN ALSO
DEAMPLIFIES LATE IN THE WEEK. ANOTHER SHORT WAVE WILL APPROACH AND
PUSH A SURFACE FRONT ACROSS THE AREA ON SATURDAY. TEMPS SHOULD BE
WARM ENOUGH THAT A PRECIP-TYPE PROBLEM IS NOT EXPECTED.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE EAST OF THE MTNS...VFR. LATEST SATELLITE
IMAGES INDICATE CLEAR SKY ACROSS THE FOOTHILLS AND PIEDMONT...WITH
INCREASING CIRRUS CLOUDS STREAMING SE ACROSS THE MID MISSISSIPPI
RIVER VALLEY. THE HIGH CLOUDS ARE ASSOCIATED WITH ARCTIC HIGH
PRESSURE PUSHING ACROSS THE GREAT PLAINS AND MID WEST. AS THE HIGH
APPROACHES...WINDS SHOULD VEER FROM THE NE AND HIGH CLOUD COVER WILL
INCREASE. BY SUNDAY AFTERNOON...THE CENTER OF THE HIGH IS EXPECTED
TO REACH THE NEW ENGLAND COAST...WITH RIDGING SOUTHWARD. THIS
PATTERN SHOULD YIELD A SE WIND...MID LEVEL CLOUDS WILL DEVELOP. TAF
DURING THIS PACKAGE WILL REMAIN DRY.

AT KAVL...CONDITIONS WILL REMAIN SIMILAR TO FOOTHILL AND PIEDMONT
TERMINALS DISCUSSED ABOVE. HOWEVER...GUSTY NNW WINDS WILL REMAIN
WITHIN THE FRENCH BROAD RIVER VALLEY THROUGH MOST OF TONIGHT. WINDS
WILL WEAKEN AROUND SUNRISE...THE VEER FROM THE SSE BY MID DAY.

OUTLOOK...A STRONG LOW PRESSURE SYSTEM WILL DEVELOP AND CROSS THE
AREA LATE SUNDAY NIGHT THRU TUESDAY...BRINGING WIDESPREAD
CLOUDS/PRECIP. THIS SYSTEM MAY PRODUCE SIGNIFICANT WINTER
IMPACTS...ESPECIALLY IN THE NC MTNS.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  92%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     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 SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY
     EVENING FOR GAZ010-017-018-026.
NC...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING
     FOR NCZ048-051>053-058-059-062-501>506.
     WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY
     EVENING FOR NCZ035>037-056-057-063>065-068>072-507>510.
     WINTER STORM WATCH FROM SUNDAY EVENING THROUGH TUESDAY MORNING
     FOR NCZ033-049-050.
     WIND CHILL ADVISORY UNTIL 10 AM EST SUNDAY FOR NCZ033-049-050.
SC...WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY
     EVENING FOR SCZ001>009.

&&

$$
SYNOPSIS...SBK
NEAR TERM...NED
SHORT TERM...TDP
LONG TERM...PM
AVIATION...NED



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