Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 081753
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1253 PM EST MON FEB 8 2016

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION TODAY...WITH A BROAD AND MOIST
AREA OF LOW PRESSURE LINGERING INTO WEDNESDAY NIGHT. CANADIAN HIGH
PRESSURE WILL THEN BUILD IN THURSDAY AND REMAIN THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1245 PM EST MONDAY...CURRENT FCST REMAINS ON TRACK THEREFORE
NO SIG CHANGES WERE MADE WITH THIS BRIEF UPDATE.  DID TWEAK TEMP/DEW
TRENDS A BIT TO BETTER ALIGN WITH OBS.  LIGHT REFLECTIVITY ACROSS
THE NC/SC PIEDMONT REGIONS LOOKS TO BE ENCOUNTERING THE DRY LOW
LEVELS AS LITTLE IF ANY PRECIP IS BEING OBSERVED AT THE SURFACE.
FULL FCST DISCUSSION TO FOLLOW WITHIN AN HOUR OR SO.

PREVIOUS DISCUSSION...WATER VAPOR IMAGERY SHOWS DEEP UPPER TROUGH
WITH EMBEDDED CYCLONE CENTERED OVER THE MIDWEST. THE TROUGH WILL
EXPAND SOUTH AND EAST THROUGH TUESDAY MORNING...BRINGING A COLD
FRONT WITH IT WHICH WILL PUSH THRU OUR CWFA TODAY. LIGHT RADAR
RETURNS ARE SEEN OVER THE OHIO VALLEY IN RESPONSE TO A CHANNELED
POCKET OF VORT AT THE LEADING EDGE OF THE TROUGH. THE VORT MAX WILL
PUSH EASTWARD ACRS THE CWFA LATER TODAY...AND STRONG QG FORCING WILL
ACCOMPANY IT THROUGH THE AREA...AS WILL PRECIPITATION. MOISTURE
DOES NOT APPEAR TO BE MUCH OF A LIMITING FACTOR EVEN EAST OF THE
MTNS. FALLING HEIGHTS WILL ALLOW LAPSE RATES TO INCREASE DURING
THE DAY AS WELL. A BULLSEYE OF CAPE VALUES UP TO NEAR 200 J/KG
IS SHOWN ON BOTH NAM AND GFS...THE GFS HAVING TRENDED TOWARD
THE NAM WHICH HAS BEEN CONSISTENTLY UNSTABLE FOR MONDAY OVER
THE PAST FEW RUNS. THIS INSTABILITY...ESPECIALLY GIVEN THE UPPER
FORCING...LENDS CONFIDENCE TO SHOWERS DEVELOPING AND SPREADING
ACROSS THE AREA TODAY. CONVECTION ALLOWING MODELS ARE SURPRISINGLY
UNRESPONSIVE...THE HI-RES WRF WINDOWS BASICALLY SUPPORTING ONLY
ISOLATED/SCHC POPS DURING THE DAY. I STILL FEEL POPS SIMILAR TO
THOSE FROM THE PREV FCST ARE WARRANTED. INCLUDED A LOW THUNDER
CHANCE OVER WRN NC BASED ON PEAK CAPES.

COLDER AIR FILTERS IN STEADILY AT 850MB THRU THE DAY. BASED ON
FAVORED BLEND /MOSTLY SREF/...TEMPS IN THE HIGHER ELEVATIONS
ARE EXPECTED TO REMAIN NEARLY STEADY...WITH VALLEYS AND THE
PIEDMONT MANAGING TO WARM ENOUGH THAT ANY PRECIP WILL INITIALLY
BE RAIN. STILL LOOKS LIKE SNOW LEVELS WILL FALL AS THE DAY
PROGRESSES. SNOW LEVELS REACH THE VALLEY FLOOR AROUND SUNSET. WITH
THE LEADING SHOT OF UPPER FORCING DEPARTING THIS EVENING...PRECIP
CHANCES TAPER OFF IN THE PIEDMONT...AND WITH TEMPS REMAINING SO WARM
THIS ROUND SHOULD END AS RAIN. HOWEVER...WHILE MODEL QPF RESPONSE
IS AGAIN QUITE LOW...A SECOND VORT LOBE ROTATING AROUND THE UPPER
CYCLONE WILL DIVE THRU THE TENN VALLEY THIS EVENING BEFORE SWINGING
ACROSS WESTERN NC IN THE WEE HOURS TUE. I FELT THIS DEPICTED WAVE
APPEARED STRONG ENOUGH TO BE ABLE TO GENERATE A FEW PIEDMONT SHOWERS
FROM THE STILL-MOIST LOW LEVELS. BY THE TIME THIS MOVES THRU...TEMPS
SHOULD BE COLD ENOUGH FOR SNOW. HOWEVER ACCUMULATION IS NOT LIKELY.

WESTERLY UPSLOPE FLOW WILL BE AN ADDITIONAL FACTOR FOR THE TENN
BORDER AREAS. THIS WILL GET UNDERWAY THIS MORNING AND REMAIN
STEADY...BUT THE LOW LEVEL WINDS VEER AND STRENGTHEN IN THE LATE
AFTERNOON AND EVENING. FURTHERMORE THAT SECOND PERIOD OF UPPER
FORCING MAY ENHANCE THE UPSLOPE-FORCED PRECIP RATES EVEN MORE. I
BLENDED IN MORE OF THE CAM/HI-RES GUIDANCE IN ORDER TO BETTER
CAPTURE THE TERRAIN INFLUENCE. NEW SNOW TOTALS MEET WARNING
CRITERIA IN THE UPSLOPE AREAS DURING THE FIRST 24 HOURS OF THE
FCST. THUS...A WINTER STORM WARNING IS BEING RAISED FOR THE TENN
BORDER ZONES. AVERY IS OMITTED SINCE THE CAM GUIDANCE PLACED MORE OF
THE SNOW WEST AND SOUTH OF THE COUNTY. ADVISORY HAS BEEN EXTENDED
THRU 12Z TUE FOR AREAS THAT WERE PREVIOUSLY IN THE ADVISORY...BUT
THAT DO NOT MEET WARNING CRITERIA. THE WARNING COULD BE EXTENDED
TO HIGHLIGHT THE CONTINUING THREAT OF NW FLOW THRU MIDWEEK.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 315 AM MONDAY...DEEP UPPER TROF REMAINS OVER THE AREA TUE AND
SLOWLY SLIDES EAST ON WED. A SERIES OF SHORT WAVES WILL MOVE THRU
THE TROF AND ACROSS THE AREA BOTH DAYS. SURGES OF CAA AND STRONG NW
FLOW WILL ACCOMPANY THE SHORT WAVES. THIS WILL LEAD TO PERIODS OF NW
FLOW SNOW SHOWERS ACROSS THE NC MTNS BOTH DAYS. EXPECT CLOUDS TO
BREAK CONTAINMENT AND SPREAD ACROSS THE FOOTHILL AND PIEDMONT...AND
POSSIBLY SNOW SHOWERS AS WELL WITH THE RELATIVELY DEEP STEEP LOW
LEVEL LAPSE RATES THAT DEVELOP. DO NOT EXPECT ANY ACCUMS FROM ANY
SNOW SHOWERS THAT DO DEVELOP OUTSIDE OF THE MTNS. HOWEVER...WITH THE
LONG DURATION OF SNOW SHOWERS ACROSS THE MTNS...AMOUNTS WILL BE UP
TO 4 INCHES IN THE USUAL LOCATIONS OF THE NRN MTNS...WITH 1 TO 2
INCHES SOUTHWARD ALONG THE TN BORDER BY THE TIME THE SNOW TAPERS OFF
WED NITE. COULD SEE SOME CLOUDS OUTSIDE OF THE MTNS ON WED BUT NO
SNOW SHOWERS EXPECTED THAT DAY. HIGHS TUE WILL BE 10 TO 20 DEGREES
BELOW NORMAL THEN FALL TO 15 TO 25 DEGREES BELOW NORMAL ON WED AS
THE COLDEST PART OF THE AIR MASS MOVES INTO THE AREA. LOWS 5 TO 10
DEGREES BELOW NORMAL TUE NITE FALL TO 10 TO 20 DEGREES BELOW NORMAL
WED NITE. WITH THE STRONG AND GUSTY WINDS CONTINUING THRU THE
PERIOD...WIND CHILL VALUES FALL INTO THE ADVISORY RANGE ACROSS THE
HIGHER ELEVATIONS TUE NITE...AND DOWN INTO THE VALLEYS ON WED
NITE...WITH WARNING LEVEL WIND CHILLS POSSIBLE IN THE HIGHER
ELEVATIONS.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 340 AM MONDAY...ALTHOUGH THE GUIDANCE SHOWS THE OVERALL
PATTERN IN THE MEDIUM RANGE IS IN DECENT AGREEMENT...THERE IS QUITE
A SPREAD IN THE DETAILS. A LONG WAVE TROF REMAINS OVER THE ERN CONUS
THRU THE PERIOD. THE FLOW FLATTENS SLIGHTLY ON THU AS THE SHORT WAVE
FROM THE SHORT RANGE MOVES EAST...THEN DEEPENS AGAIN FRI AND SAT AS
ANOTHER SERIES OF SHORT WAVES DIG INTO THE TROF. THE ECMWF IS DEEPER
AND STRONGER WITH THE TROF AS A CLOSED UPPER LOW DIVES INTO THE MID
ATLANTIC...WHILE THE GFS KEEPS THE UPPER LOW OVER QUEBEC. HEIGHTS
THEN RISE ON SUN IN THE GFS AS THE TROF AXIS MOVES EAST...WHILE THE
ECMWF KEEPS HEIGHTS LOW AS THE TROF ONLY SLOWLY MOVES EAST.

AT THE SFC...THE GUIDANCE AGREES ON A CLIPPER SYSTEM AFFECTING THE
AREA...BUT THE GFS IS FASTER AND WEAKER WITH THE SYSTEM WHILE THE
ECMWF IS STRONGER AND SLOWER. BOTH ALSO HAVE A REINFORCING VERY COLD
AIR MASS MOVING IN BEHIND THE SYSTEM...BUT THE GFS BRINGS IT IN
SOONER AND MODERATES IT FASTER. GIVEN THESE DIFFERENCES....HAVE GONE
WITH A GUIDANCE BLEND. THIS MEANS A DRY FCST FOR THU...WITH CHANCE
POP FOR THE TN BORDER COUNTIES FRI AND FRI NITE...WITH SLIGHT CHANCE
POP ELSEWHERE...THEN DRY FCST AGAIN FOR SAT AND SUN. EVEN THOUGH
TEMPS REMAIN NORMAL THRU THE PERIOD...DO HAVE A WARMING TREND THRU
SAT WITH COOLING AGAIN FOR SUN. WIND CHILL VALUES WILL AGAIN
APPROACH ADVISORY LEVELS ACROSS THE HIGHER ELEVATIONS SAT NITE. THAT
SAID...THIS IS A LOW CONFIDENCE FORECAST GIVEN THE WIDE RANGE IN THE
GUIDANCE.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
AT KCLT AND ALL SITES OUTSIDE THE MTNS...VFR THROUGH THE PERIOD WITH
THE POSSIBLE EXCEPTION OF A BRIEF WINDOW OF MVFR VISB ASSOCIATED
WITH LIGHT PREFRONTAL SHRA.  INITIALIZED TAFS WITH VCSH AND MID
LEVEL VFR CIGS WITH A 4HR TEMPO FOR SHRA AS UPPER VORT MAX SLIDES
THROUGH THE REGION AHEAD OF THE SURFACE FRONT WHICH WILL YIELD
LIGHT PRECIP AROUND THE AREA.  CIGS SHOULD REMAIN AT LOW VFR
LEVELS THROUGH THE AFTERNOON BEFORE INCREASING TO MID/HIGH VFR
AS THE COLD FRONT SWEEPS EAST.  IN RESPONSE...WINDS WILL VEER NW
AND REMAIN ELEVATED THROUGH THE NIGHT WITH PERHAPS AN OCCASIONAL
GUST AS COLD ADVECTION PREVAILS...WITH INCREASED GUSTING LIKELY
ON TUESDAY MORNING AMIDST SOLIDLY VFR SKIES.

AT KAVL...TRENDS SIMILAR TO THAT OF THE ABOVE DISCUSSION...HOWEVER
WITH FASTER TIMING AND LOWERED FLIGHT CATEGORIES.  INITIALIZED TAF
WITH GUSTING NW WINDS AS THE FRONT HAS CLEARED THE AIRFIELD...WITH
LOW VFR STRATUS PREVAILING.  COLD ADVECTION IS UNDERWAY THEREFORE
A TEMPO FOR SHRASN CONTINUES THROUGH THE AFTERNOON AS GUIDANCE
FAVORS POSSIBLE PRECIP YIELDED FROM SECOND SHORTWAVE PASSING BY.
OTHERWISE...THINK ANY FURTHER SN ACCUMS WILL REMAIN TIED TO THE
TN LINE THUS ALLOW FOR SN MENTION TO LAPSE BY 00Z HOWEVER WITH
PERSISTENT LOW VFR CIGS AND ELEVATED NW FLOW THROUGH THE PERIOD.

OUTLOOK...SEVERAL STRONG UPPER DISTURBANCES EMBEDDED IN A DEEP
UPPER TROUGH WILL SWING ACROSS THE AREA THRU WEDNESDAY. MOISTURE
AND COLD AIR WILL CONTINUE TO FLOW INTO THE AREA DURING THIS
TIME PERIOD. RESTRICTIONS WILL BE POSSIBLE...PARTICULARLY IN THE
MOUNTAINS WHERE THERE ARE HIGH CHANCES OF ACCUMULATING SNOW.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH  83%     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...NONE.
NC...WINTER WEATHER ADVISORY UNTIL 7 AM EST TUESDAY FOR NCZ033-053-
     062-063.
     WINTER STORM WATCH FROM TUESDAY MORNING THROUGH THURSDAY
     MORNING FOR NCZ033-048>052-058-059-062.
     WINTER STORM WARNING UNTIL 7 AM EST TUESDAY FOR NCZ048>052-058-
     059.
SC...NONE.

&&

$$
SYNOPSIS...RWH
NEAR TERM...CDG/WIMBERLEY
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CDG


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