Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 221946
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
246 PM EST THU JAN 22 2015

.SYNOPSIS...
A DEVELOPING AREA OF LOW PRESSURE WILL TRACK ALONG THE GULF AND
SOUTH ATLANTIC COASTS THROUGH FRIDAY NIGHT...BEFORE MOVING FURTHER
UP THE EAST COAST OVER THE WEEKEND. THE LOW WILL BRING WIDESPREAD
PRECIPITATION OVER OUR AREA FRIDAY INTO SATURDAY. HIGH PRESSURE
BRIEFLY BUILDS IN SUNDAY...BEFORE A COLDER LOW PRESSURE SYSTEM
AFFECTS THE FORECAST AREA SUNDAY NIGHT INTO TUESDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 220 PM...DRAMATIC WEATHER CHANGE STILL ON TAP AS UPPER LOW
OVER THE FOUR CORNERS REGION OPENS UP AND MOVES EAST TO THE WRN GULF
COAST TONIGHT AND FRIDAY. AT THE SFC...HIGH PRESSURE BUILDS INTO THE
MID ATLANTIC AS A LOW PRESSURE SYSTEM MOVES FROM THE TX GULF COAST
TO THE THE GA/SC COASTAL PLAIN BY THE END OF THE DAY FRIDAY. THE
GUIDANCE LOOKS TO BE IN GENERAL AGREEMENT THAT PRECIP WILL CROSS THE
SAVANNAH RIVER AND MOVE INTO THE SWRN NC MTNS LATE TONIGHT OR EARLY
FRI MORN. PRECIP THEN QUICKLY SPREADS ACROSS THE AREA FRIDAY AS
ISENTROPIC LIFT...UPPER DIVERGENCE AND DEEP FORCING MOVE IN. HAVE
POP RAMPING UP TO NEAR 100 PERCENT ACROSS THE ENTIRE CWFA BY 18Z.
QPF WILL RANGE FROM ONE-HALF TO ONE INCH ACROSS THE AREA.

NOW TO THE DIFFICULT PART. WHILE PRECIP IS A VIRTUAL CERTAINTY...P-
TYPE REMAINS A LITTLE UNCERTAIN. SFC TEMP...PARTIAL THICKNESSES...
AND FCST SOUNDINGS HAVE WARMED ON ALL MDLS. THIS IS LIKELY DUE TO
THE TRANSIENT NATURE OF THE HYBRID COLD AIR DAMMING HIGH THAT SETS
UP OVER THE MID ATLANTIC. IN FACT...THE GUIDANCE IS EERILY SIMILAR
SHOWING COLD AIR AT PRECIP ONSET WITH MID LEVEL WARMING THEN LOW
LEVEL WARMING AS THERE IS A LACK OF A CONTINUED COLD DRY FETCH IN
THE NON-CLASSICAL CAD. WOULD NOT BE SURPRISED TO SEE A MIX OF RAIN
AND SLEET ACROSS THE AREA AS PRECIP MOVES IN...AS OFTEN OCCURS IN
THESE EVENTS. HOWEVER...RAIN WILL BE THE PREDOMINANT P-TYPE EAST AND
SOUTH OF THE BLUE RIDGE.

FROM THE BLUE RIDGE WEST...EXPECT A MIX OF SNOW/SLEET/RAIN AND
FREEZING RAIN FOR ALL BUT THE FAR SWRN NC MTNS. THIS MIX WILL CHANGE
TO RAIN/FREEZING RAIN...THEN ALL RAIN FROM SW TO NE AS THE MID LEVEL
WARMING OCCURS. THAT SAID...THE HIGHEST ELEVATIONS ALONG THE NRN
BLUE RIDGE COULD HOLD ON TO FREEZING RAIN THRU THE DAY DEPENDING ON
HOW THE STRENGTH OF THE BARRIER JET AND MECHANICAL FORCING FROM THE
UPSLOPE FLOW. STILL...GIVEN THE TRANSITIONAL P-TYPES AND RELATIVE
WARMING EXPECTED...THESE AREAS SHOULD SEE LESS THAN A HALF INCH OF
SNOW/SLEET WITH AROUND A TENTH OF AN INCH OF ICE ACCRETION. AGAIN...
THE HIGHEST ACCUMS WILL BE NEAR THE BALSAMS AND ALONG THE NRN BLUE
RIDGE.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 230 PM THURSDAY...THE SHORT TERM PICKS UP AT 00Z
SATURDAY...WITH MODELS IN GOOD AGREEMENT ON THE SFC LOW CENTERED
INVOF TALLAHASSEE FL...WITH A SHARP H5 TROF AXIS ACRS THE LWR MS
VALLEY. FRIDAY EVENING LOOKS LIKE A CONTINUED TRANSITION TO ALMOST
ALL RAIN ACRS THE CWFA...AS LLVL FLOW TURNS FROM SE TO SW...AND A
DRY SLOT PUNCHES INTO THE SRN APPALACHIANS FROM THE SW. TEMPS MAY BE
ABLE TO HOLD AROUND 30-32 ALONG THE ERN SLOPES OF THE NRN NC BLUE
RIDGE. HOWEVER...ADDITIONAL ICE ACCUMS SHUD BE VERY LIGHT...WITHIN A
LULL IN PRECIP. BY 12Z SAT...A DEFORMATION ZONE WITHIN THE MID LVL
TROF WILL ENTER THE NC MTNS...BRINGING FALLING MID LVL HEIGHTS (AND
SNOW LEVELS)...WHILE INCREASING THE POP. TAKING A BLEND OF THE
NAM/SREF WITH THE WPC QPF (THROWING OUT THE GFS)...I GET 1-2" OF
ADDITIONAL SNOW ACCUM MAINLY ABOVE 3500 FT SATURDAY MORNING. THE
DEFORMATION ZONE WILL TRANSLATE EAST QUICKLY...WITH POPS TAPERING
OFF BY MIDDAY. BY SATURDAY AFTN...NWLY 850 MB FLOW WILL
INCREASE...KEEPING A SLGT CHC TO LOW-END CHC OF SNOW SHWRS ALONG THE
TN/NC BORDER. GRADUAL CLEARING IS EXPECTED EAST OF THE MTNS. TEMPS
WILL HOVER IN THE 30S ACRS THE AREA FRIDAY NIGHT TO NEAR 40 IN THE
UPR SAVANNAH VALLEY...THEN WARM LITTLE ABOVE 3500 FT...BUT INTO THE
MID-UPR 40S ACRS THE PIEDMONT ON SATURDAY.

SATURDAY NIGHT AND SUNDAY...A BROAD H5 TROF WILL LINGER IN WAKE OF
THE SATURDAY TROF PASSAGE. THE CWFA WILL BE IN BETWEEN A NOREASTER
AFFECTING THE MID ATLANTIC/NEW ENGLAND...AND A CLIPPER THAT WILL BE
DIVING INTO THE WRN GREAT LAKES. ANOTHER VORT MAX WILL CROSS THE NC
MTNS SATURDAY NIGHT WITHIN THE LONGWAVE TROF. IT WILL HAVE LITTLE
MOISTURE TO WORK WITH...BUT THE NAM AND GFS BOTH SHOW A HUNDREDTH OR
TWO OF QPF RESPONSE ALONG THE TN/NC NWLY FLOW UPSLOPE AREAS. I
BUMPED UP POPS BACK TO CHC SATURDAY NIGHT FROM MADISON TO AVERY
COUNTY FOR SNOW SHWRS. LITTLE OR NO ACCUMS ARE EXPECTED. THE LLVL
FLOW WILL BACK TO W-SWLY ON SUNDAY...AND GUIDANCE IN GOOD AGREEMENT
ON A DRY DAY ACRS THE CWFA AHEAD OF THE APPROACHING CLIPPER SYSTEM.
TAKING A MODEL BLEND...I GET NEAR NORMAL TEMPS UNDER PARTLY CLOUDY
SKIES.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 200 PM THU...LONGWAVE TROUGH PERSISTS OVER THE ERN CONUS THRU
THE MOST OF THE MEDIUM RANGE. THE UPPER PATTERN IS INITIALLY LOCKED
IN PLACE BY A REX BLOCK OVER THE WEST COAST...WHICH BREAKS DOWN
MONDAY. GLOBAL MODELS DIFFER IN HOW THE PATTERN SUBSEQUENTLY EVOLVES
OVER THE WEST BUT AGREE RIDGING WILL OCCUR OVER THE EAST BY WED
NIGHT. WHILE THE ERN TROUGH REMAINS IN PLACE...A SERIES OF CLIPPER-
LIKE SHORTWAVES WILL MOVE ACROSS OUR AREA. MEAN NWLY FLOW WILL
CONTINUE...SUGGESTING A CONTINUED FOCUS FOR PRECIP CHANCES ALONG THE
WRN FACING SLOPES OF THE NC MTNS. THE PASSING SHORTWAVES APPEAR
CAPABLE OF FORCING VERY LIGHT PRECIP OVER THE PIEDMONT...MAINLY THE
NC SIDE. DOWNSLOPING WILL BE WORKING AGAINST SAID FORCING AND ONLY
LOW POPS AND QPF WILL BE ADVERTISED THERE. IN THE MTNS...BLENDED QPF
FROM THE GLOBAL MODELS AND AN EXPECTATION OF PREDOMINANTLY SNOW AS A
PTYPE SUGGEST TOTALS GENERALLY 1-2 INCHES IN THE 12 HR PERIODS
SUNDAY NIGHT AND MONDAY.  THIS MAY WARRANT A WINTER WX ADVY.

THE 22/12Z GFS CONTINUES TO EXHIBIT A COUPLE OF KEY DIFFERENCES FROM
THE CORRESPONDING GEM OR EC. THE FIRST IS IN THE WELL DEFINED
SHORTWAVE CROSSING THE AREA MONDAY...WHICH DOES NOT COME AS FAR SOUTH
ON THE GFS PROGS AND IS FOLLOWED BY A SECONDARY CHANNELED AREA OF
VORT. THE EC DEPICTS A MORE BROAD TROUGH WITH DISTINCT EDDIES DARTING
THROUGH WITHIN. THE EC BRINGS ANOTHER WAVE OF LIGHT QPF INTO THE AREA
TUESDAY AS A RESULT...WHEN TEMPS HAVE COOLED TO BECOME A LITTLE MORE
SUPPORTIVE OF WINTRY PRECIP. THE GEM LOOKS MORE LIKE THE EC THAN THE
GFS BUT DOES NOT RESPOND WITH QPF TUE. RUN-TO-RUN CONSISTENCY IS NOT
THAT GREAT FOR ANY OF THE MODELS WITH THE SMALLER SCALE WAVES AND
ASSOCIATED QPF. WITH THIS PACKAGE THE PIEDMONT POPS HAVE BEEN
EXPANDED SLIGHTLY THRU EARLY TUE ON ACCOUNT OF CONTINUED HINTS AT
PRECIP.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS SHOULD PREVAIL THRU THE
EVENING...WITH CONDITIONS DETERIORATING FROM WEST TO EAST NEAR
DAYBREAK. AN UPPER LEVEL JET STREAK WILL CONTINUE TO BRING MID AND
HIGH LEVEL CLOUDS OVER THE AREA THRU THE AFTERNOON. WIND SHOULD BE
LIGHT BUT WILL BE QUITE VARIABLE THRU THE AFTERNOON AS HIGH PRESSURE
SLOWLY BUILDS IN FROM THE NORTH AND A WEAK LEE TROF DEVELOPS.
MOISTURE PROFILES WILL CONTINUE TO DEEPEN OVERNIGHT WITH CEILINGS
GRADUALLY LOWERING FROM THE SW. PRECIP SHOULD BEGIN TO SPREAD IN
FROM THE SW AFTER MIDNIGHT...BUT WILL HAVE DIFFICULTY REACHING THE
GROUND AT FIRST. THINK LIGHT RAIN WILL REACH KAND AROUND 12Z WITH
PRECIP DEVELOPING EAST OF THERE QUICKLY THRU THE MORNING. KAVL HAS
THE BEST CHC OF SEEING ANY WINTRY PRECIP AT ONSET...WITH SOME CHC AT
KHKY. THE OTHER SITES SHUD SEE ONLY RAIN. RESTRICTIONS WILL QUICKLY
DEVELOP THRU THE MORNING AS PRECIP RATES INCREASE. IFR CIGS...AND
POSSIBLY VSBY...LIKELY FOR THE WRN SITES BEFORE 18Z...WITH ONLY A
SMALL CHC AT KCLT. N TO NE WINDS INCREASE IN SPEED THRU THE NITE AND
BECOME GUSTY AT THE WRN SITES AFTER DAYBREAK. NLY WIND BECOMES SLY
AT KAVL.

OUTLOOK...PRECIPITATION AND RESTRICTIONS CONTINUE FRIDAY AFTERNOON
AND NIGHT. ANY WINTRY PRECIP AT KHKY WILL BE SHORT LIVED...AND SHUD
BECOME ALL RAIN DURING THE AFTERNOON AT KAVL. ANOTHER SYSTEM ON
MONDAY COULD BRING MORE RESTRICTIONS OVER THE MTNS MAINLY NEAR THE
TN BORDER THROUGH MONDAY NIGHT.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     MED   68%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     LOW   59%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     MED   76%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     MED   66%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     LOW   58%
KAND       HIGH 100%     HIGH 100%     HIGH  88%     MED   71%

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...NONE.
NC...WINTER WEATHER ADVISORY FROM 6 AM FRIDAY TO NOON EST SATURDAY
     FOR NCZ033-048>052-058-059-062>064-501-503-505.
SC...NONE.

&&

$$
SYNOPSIS...WIMBERLEY
NEAR TERM...RWH
SHORT TERM...ARK
LONG TERM...WIMBERLEY
AVIATION...RWH



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