Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 240209
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
909 PM EST MON FEB 23 2015

.SYNOPSIS...
AN AREA OF HIGH PRESSURE WILL REMAIN ACROSS THE REGION TODAY...WHILE
A WEAK...BUT MOIST UPPER DISTURBANCE CROSSES OVERHEAD LATE TONIGHT
THROUGH TUESDAY MORNING. A MOIST AND WINTRY LOW PRESSURE SYSTEM WILL
TRACK ACROSS SOUTHERN GEORGIA AND UP THE CAROLINA COAST WEDNESDAY
NIGHT THROUGH THURSDAY MORNING...BEFORE COLD CANADIAN HIGH PRESSURE
BUILDS BACK IN FRIDAY AND WARMS THROUGH SUNDAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
0200 UTC UPDATE...POPS...QPF...AND SNOWFALL AMOUNTS WERE UPDATED
BASED ON THE LATEST RADAR TRENDS...MODEL DATA...AND COLLABORATION
WITH NEIGHBORING OFFICES. AS A RESULT...IT APPEARS THAT OUR SOUTHERN
PIEDMONT COUNTIES...NC BLUE RIDGE ZONES...SPRTANBURG CO SC AND AND
POLK CO NC WILL REACH WINTER WEATHER ADVISORY CRITERIA...AND WILL BE
ADDED TO THE WINTER WEATHER ADVISORY.

2315 UTC UPDATE...SKY COVER WAS ADJUSTED PER SATELLITE IMAGERY.
POPS...QPF...AND SNOWFALL TOTALS WERE ADJUSTED FOR A BETTER FOR WITH
NEIGHBORING OFFICES...AND THE LATEST EXPECTED TIMING OF
PRECIPITATION ARRIVAL.

AS OF 245 PM...RECENT SATELLITE IMAGES INDICATED CLEARING ACROSS THE
FOOTHILLS AND SPREADING INTO THE PIEDMONT. TEMPERATURES HAVE
RESPONDED QUICKLY TO THE INCREASING SUN...RESULTING IN TEMPERATURES
WELL ABOVE THE PREVIOUS FORECAST. I HAVE POPULATED WITH THE
OBS...EXPECT THAT TEMPS HAVE PEAKED WITH INCREASING CAA THE REST OF
THIS AFTERNOON.

TONIGHT...THE APPROACH OF H3 JET COMBINED WITH A WEAK MID LEVEL
DISTURBANCE WILL PROVIDE FORCING ACROSS THE REGION TONIGHT. AT
19Z...THE PRECIP ASSOCIATED WITH THESE FEATURES WAS MOVING EAST
ACROSS THE SOUTHERN MISSISSIPPI RIVER VALLEY. AS A EMBEDDED L/W TROF
RIPPLES ACROSS THE CENTRAL CONUS LATE TONIGHT...AN INVERTED SFC TROF
IS EXPECTED TO DEVELOP ALONG AND WEST OF THE SAVANNAH RIVER VALLEY.
THE COMBINATION OF LLVL CONVERGENCE...UPSLOPE FLOW...AND MID/UPPER
FORCING SHOULD SUPPORT AN EXPANDING AREA OF PRECIP LATE TONIGHT
ACROSS THE MTNS AND UPPER SAVANNAH RIVER VALLEY. DURING THE PRE DAWN
HOURS...HIGH PRESSURE RIDGING WILL RAPIDLY INCREASE ACROSS THE
CENTRAL CAROLINAS...RESULTING IN COLD AIR DAMMING. THIS PATTERN WILL
SUPPORT CAA ACROSS THE FORECAST AREA THROUGH SUNRISE. THERMAL
PROFILES INDICATES THAT THE PRECIP WILL FALL PRIMARILY AS SNOW.

ON TUESDAY...THE AREA ACROSS THE I-77 CORRIDOR SHOULD SEE THE
GREATEST ISENTROPIC LIFT ON THE WEST SIDE OF THE CAD. THE ISENTROPIC
LIFT AT 300K SHOULD BEGIN SHORTLY AFTER SUNRISE AND CONTINUE THROUGH
MID DAY. PRECIP SHOULD DECREASE THROUGH THE REST OF THE DAY...WITH
GENERALLY DRY CONDITIONS ACROSS THE FOOTHILLS AND PIEDMONT DURING
THE AFTERNOON. WEST FLOW WILL SUPPORT SCT UPSLOPE SHOWERS ALONG THE
TN BORDER THROUGH THE REST OF THE AFTERNOON.

FORECAST SNOWFALL IS FORECAST TO RANGE FROM 1 TO 3 INCHES ACROSS THE
NC MTNS...WITH AROUND AN INCH ACROSS THE NORTHERN SAVANNAH RIVER
VALLEY AND WESTERN UPSTATE OF SC...WITH A DUSTING ACROSS THE EASTERN
UPSTATE TO THE CLT METRO AREA. THE GREATEST SNOWFALL RATES SHOULD
FALL DURING THE MORNING RUSH HOURS.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM MONDAY...AN ACTIVE SOUTHERN STREAM INTERACTING WITH THE
QUASI-STATIONARY POLAR FRONT TO THE SOUTH WILL MAKE FOR INTERESTING
FORECASTING THIS WEEK. HOWEVER...THE BEGINNING OF THE SHORT RANGE
WILL BE BEGIN ON THE QUIET SIDE AS WEAK HIGH PRESSURE RIDGES INTO
THE AREA FORM THE WEST AS A FRONTAL WAVE MOVES WELL OFF THE EAST
COAST. THEREFORE...EXPECT GENERALLY DRY CONDITIONS TO PERSIST TUE
NIGHT THROUGH PERHAPS THE BULK OF WED. DURING THAT TIME...A MORE
POTENT SOUTHERN STREAM WAVE WILL BE EJECTING OUT OF THE DESERT SW
INDUCING CYCLOGENESIS OVER THE NORTHERN GOM ON WED WHICH IS FORECAST
TO SCOOT EAST ALONG THE FRONT THROUGH NORTH FLORIDA AND THEN INTO
THE ATLANTIC BY EARLY THU. AS THE WAVE MOVES EASTWARD...UPPER
DIVERGENCE AND ISENTROPIC LIFT INCREASE RAPIDLY ACROSS NE GA AND THE
WESTERN CAROLINAS WITH PRECIP SPREADING QUICKLY OVER THE REGION FROM
SOUTH LATE WED INTO WED NIGHT. THERE IS CERTAINLY MODEL CONSENSUS AT
THIS POINT THAT PRECIP WIL OCCUR...SO WILL BE INCREASING POPS
CONSIDERABLY INTO THE CATEGORICAL/LIKELY RANGE SUBJECT TO
COLLABORATION WITH OUR NEIGHBORING OFFICES.

THE MOST DIFFICULT PART OF THE FORECAST IS AS USUAL TRYING TO PIN
DOWN THE DETAILS MOST NOTABLY IN REGARD TO THE AMOUNT OF QPF AND THE
THERMAL STRUCTURE OF THE ATMOSPHERE PARTICULARLY IN OUR SOUTHHERN
PIEDMONT AREAS WHERE THERE MAY BE A TIGHT GRADIENT BETWEEN FROZEN
PRECIP AND RAIN. THE OPERATIONAL GFS/NAM SHOW SOME SUBTLE DETAILS IN
THE THERMAL PROFILES ACROSS THE PIEDMONT WITH THE GFS SOMEWHAT
WARMER. ALSO THE 12Z GFS CONTINUES TO BE ON THE LOWER END OF THE QPF
ENVELOP. WPC`S DAY3 FORECAST IS FAVORING HIGHER QPF BASED ON
ENSEMBLES WHICH TRANSLATES INTO WARNING LEVEL SNOW ACROSS MUCH OF
THE AREA. LOOKING AT THE SREF PLUMES THERE IS A LARGE SPREAD IN THE
MEMBERS. FOR INSTANCE AT CLT...THERE IS A RANGE FROM OVER 10 INCHES
TO ESSENTIALLY A DUSTING WITH THE MEAN SOMEWHERE AROUND 3 INCHES OR
SO. THE CONCERN ACROSS THE PIEDMONT IS THAT THE BOUNDARY LAYER WILL
BE SLOWER TO COOL THAN WHAT THE MODELS ARE INDICATING AS MAX TEMPS
SHOULD BE WELL INTO THE 40S WED AFTERNOON. ALSO...ALL THE COOLING
WILL BE BE MOSTLY DYNAMICALLY INDUCED WITH NO COLD HIGH SITUATED
DIRECTLY TO THE NORTH. IN FACT...A BLEND OF THE NAM/GFS SURFACE WET
BULBS OUTSIDE THE MOUNTAINS SHOW MID TO UPPER 30S AT 00Z THU...
SLOWLY FALLING TO THE UPPER 20S ACROSS THE NORTHERN NC PIEDMONT TO
THE MID 30S SOUTHERN GREENWOOD COUNTY DURING WED NIGHT. IN THE
ABSENCE OF A WARM NOSE...SNOW GENERALLY OCCURS WHEN SURFACE WET BULB
TEMPS ARE AT OR BELOW 33 DEGREES. THE BOTTOM LINE IS THAT THERE IS A
GOOD CHANCE THAT SOME OF THE QPF ACROSS PORTIONS OF THE PIEMDONT
WILL BE USED UP AS RAIN BEFORE TRANSITIONING TO SNOW. ALSO...WITH
THE AMOUNT OF QPF IN QUESTION... DO NOT PLAN ON ANY WINTER STORM
WATCH HEADLINES YET. IF THE THE LOWER GFS QPF WERE TO VERIFY...
WARNING LEVEL SNOW WOULD BE MARGINAL AT BEST.

PRECIP WILL QUICKLY END EAST OF THE MOUNTAINS EARLY ON THU EXCEPT
FOR SOME LINGERING SNOW SHOWERS IN THE MOUNTAINS. USED A MODEL
CONSENSUS FOR MOST FIELDS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 210 PM MONDAY...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 /02Z TUESDAY THROUGH SATURDAY/...
AT KCLT...LIGHT SNOWFALL WILL SPREAD EAST OVERNIGHT...AND A GUIDANCE
CONSENSUS SUPPORTS A LOW VFR CIG LOWERING TO MVFR BEFORE DAWN...WITH
THE VSBY LOWERING TO MVFR AROUND THE SAME TIME. VSBY WILL RETURN TO
VFR AFTER DAYBREAK...BUT THE MVFR CIG IS EXPECTED TO PERSIST...
     EVEN AFTER SNOW ENDS AT MIDDAY. SNOW ACCUMULATIONS WOULD BE QUITE
LIGHT. WINDS WILL FAVOR THE NE UNTIL MIDDAY TUESDAY...WHEN THEY VEER
TO SE AND BECOME LIGHT.

ELSEWHERE...CIGS ARE EXPECTED TO LOWER FROM LOW VFR TO MVFR THIS
EVENING WHILE SNOW SPREADS EAST ACROSS THE AREA...WITH IFR AT KAVL
AND SC SITES BEFORE DAWN. KAVL AND SC CIGS RETURN TO MVFR IN THE
AFTERNOON. GUIDANCE SUPPORTS MVFR VSBY IN SNOW LATE TONIGHT...WITH
IFR AT KAVL. VSBY RETURNS TO VFR BY EARLY AFTERNOON AS SNOW
DIMINISHES. FOOTHILL WINDS WILL FAVOR THE NE OVERNIGHT AND EARLY
TUESDAY...WHILE THE VEER FROM N TO SE AT KAVL. WINDS VEER SE AT
FOOTHILL SITES TUESDAY AFTERNOON AND BECOME LIGHT. SNOW
ACCUMULATIONS WOULD BE RATHER LIGHT.

OUTLOOK...WAVES OF LOW PRESSURE MOVING EASTWARD ALONG THE FRONT
COULD KEEP THE WEATHER IN THE CAROLINAS UNSETTLED THIS WEEK.
HOWEVER...CONFIDENCE IS TOO LOW WITH ANY OF THESE WAVES TO INDICATE
ANY GOOD CHANCES OF RESTRICTIONS.

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 TUESDAY FOR GAZ010-017-
     018-026-028-029.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR NCZ053-
     062>065-501-503-505-507-509-510.
     WINTER WEATHER ADVISORY UNTIL 4 PM EST TUESDAY FOR NCZ033-
     048>052-058-059.
SC...WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR SCZ001>007-
     010>012-019.

&&

$$
SYNOPSIS...SBK
NEAR TERM...JAT/NED
SHORT TERM...LG
LONG TERM...JDL
AVIATION...JAT



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