National Weather Service Raw Text Product

190 
FXUS62 KGSP 260005
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
705 PM EST MON FEB 25 2013

.SYNOPSIS...
NORTH OF A DEVELOPING WARM FRONT...MOISTURE WILL SPREAD ATOP OUR 
REGION FROM THE GULF OF MEXICO. STRONG LOW PRESSURE WILL DRIVE
A COLD FRONT ACROSS OUR AREA ON TUESDAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 630 PM...THE FORECAST APPEARS ON TRACK. I WILL UPDATE THE 
T/TD/WINDS TO LATEST OBSERVATIONS.

AS OF 545 PM...I WILL UPDATE THE FORECAST THROUGH TUESDAY. LATEST 
REGIONAL RADAR COMPOSITE INDICATES LITTLE TO NO RETURNS ACROSS THE 
FORECAST AREA AND ACROSS THE UPSTREAM REGION. THEREFORE...I HAVE 
SLOWED THE ARRIVAL OF CATE POPS UNTIL AFTER MIDNIGHT. THEN...ALL 
SOLUTIONS INDICATE THAT WIDESPREAD PRECIP WILL OCCUR DURING THE PRE 
DAWN HOURS AND EARLY DAYTIME HOURS ON TUESDAY...BEFORE A DRY SLOT 
ARRIVES IN THE AFTERNOON. 

THE SLOWING OF THE ARRIVAL OF POPS AND SLIGHT QPF FORECAST WILL HAVE 
AN IMPACT ON THE ICE FORECAST LATE TONIGHT AND TUESDAY MORNING. THE 
LATEST FORECAST WILL FEATURE VALUES APPROACHING 0.25 ALONG THE EAST 
FACING SLOPES OF THE NC NRN MTNS...ELSEWHERE ACROSS THE ADJACENT 
FOOTHILLS AND VALLEY...VALUES WILL REMAIN LESS THAN A TENTH OF AN 
INCH. THE CURRENT WSW APPEARS WELL PLACED AND TIMED FOR ADVISORY 
FREEZING RAIN. ONE NOTE...THE SREF GUIDANCE APPEARS VERY HIGH ON 
FZRA AMOUNTS. THEREFORE...THE SREF PLUMES AND ANY GUIDANCE BASED ON 
THE SREF WILL NOT BE CONSIDERED.

AS OF 2 PM MON...RIDGE OF HIGH PRESSURE EXTENDING DOWN THE ERN 
APPALACHIANS INDICATES CAD WEDGE ALREADY IN PLACE. STRENGTHENING SFC 
LOW OVER ARKLATEX REGION WILL MOVE INTO THE LOWER OHIO VALLEY BY 
EARLY TUESDAY...PRODUCING INCREASINGLY STRONG SOUTHERLY FLOW OVER 
THE TOP OF THE WEDGE. ISENTROPIC LIFT WILL INCREASE ACCORDINGLY 
GOING INTO THE EVENING. PRECIP CHANCES THIS AFTERNOON WILL BE ON THE 
LOWER END WITH MEDIOCRE CONDENSATION PRESSURE DEFICITS SEEN ON THE 
ISENTROPIC SURFACES. HOWEVER THE FLOW IS STRONG AND THE MODELS DO 
SQUEEZE OUT SOME LIGHT QPF. 850MB LLJ INCREASES TO 50-70KT 
/STRONGEST OVER THE MOUNTAINS/ LATE TONIGHT AS UPPER LOW ADVANCES 
AND HEIGHT GRADIENT TIGHTENS. THIS WILL MAXIMIZE MOISTURE TRANSPORT 
AND I EXPECT PEAK PRECIP COVERAGE IN THE WEE HOURS TUE MORNING. 
CATEGORICAL POPS ARE INCLUDED ACROSS THE ENTIRE CWFA.

COLD WEDGE SHOULD ONLY STRENGTHEN WITH THE PRECIP SPREADING IN THIS 
EVENING SO FAVORED LOW SIDE OF GUIDANCE TEMPS TONIGHT...NEAR RAW 
NAM/GFS. THIS BRINGS TEMPS INTO THE MID 30S ACROSS MOST OF THE CWFA 
AND NEAR OR BELOW FREEZING IN THE HIGHER TERRAIN. DEPTH OF THE 
MOISTURE...STRENGTH OF THE WINDS...AND THE UPPER SUPPORT ALL WARRANT 
FAIRLY ROBUST QPF. WITH THE QPF AND TEMPS...PLUS THE STRENGTH OF THE 
WARM NOSE ABOVE THE WEDGE...THE MTNS/FOOTHILLS COULD SEE SOME ICE 
ACCUMULATE OVERNIGHT. A WINTER WX ADVY HAS BEEN POSTED. IMPACT WILL 
BE NEGATED SOMEWHAT BY THE CONTINUING RAINFALL AS TEMPS WARM UP 
TOMORROW MORNING WHICH SHOULD MELT ANY ICE.

STRENGTH OF THE LLJ CONTINUES TO SUPPORT HIGH WIND WARNING 
PREVIOUSLY ISSUED FOR THE HIGHER ELEVATIONS OF THE MTNS AS WELL AS 
THE WIND ADVY IN LOWER ELEVATIONS. COLD FRONT LOOKS TO BEGIN PUSHING 
INTO THE SW MTNS BY LATE MORNING...WITH DRY SLOT WORKING IN BEHIND 
IT...AND ERODING THE WEDGE. PRECIP WILL DIMINISH FROM THE WEST 
THOUGH WIDESPREAD RAINFALL WILL CONTINUE INTO AT LEAST EARLY 
AFTERNOON EAST OF I-77. MODELS INCLUDING SOME SREF MEMBERS DEVELOP A 
TRIPLE-POINT LOW NEAR CHARLOTTE AS THE FRONT INTERACTS WITH THE 
WEDGE BOUNDARY. SPECTACULAR LLVL SHEAR WILL STILL BE PRESENT AND 
ENHANCED NEAR SFC WARM ADVECTION WITH THE LOW COULD ALLOW SFC BASED 
INSTABILITY. THUS THERE IS A SMALL SEVERE RISK...MAINLY SOUTH AND 
EAST OF CHARLOTTE...TOMORROW AFTN. SPC HAS INCLUDED PORTIONS OF 
UNION CO NC AND CHESTER CO IN THE DAY 2 OUTLOOK FOR THIS REASON. 
SOME SLIGHT ELEVATED INSTABILITY WILL BE PRESENT ANYWAY FOR PARCELS 
LIFTED FROM THE WARM NOSE SO THERE IS A DECENT CHANCE OF THUNDER 
OVER MUCH OF THE SE HALF OF THE CWFA TOMORROW...EVEN IF THE TRIPLE 
POINT FALLS FURTHER EAST AND SEVERE WX THREAT IS MITIGATED OVER OUR 
AREA.

TEMPS COULD SHOOT UP QUICKLY AS THE WEDGE IS ERODED...PERHAPS 
TOPPING OUT AROUND NORMAL IN THE FAR SOUTH AND SOUTHWEST...BUT WILL 
REMAIN WELL BELOW NORMAL NORTH AND EAST WHERE THE WEDGE WILL LAST 
INTO THE AFTERNOON.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM EST MONDAY...THE SHORT TERM PERIOD BEGINS WITH AN 
OCCLUDED FRONT MOVING EASTWARD AWAY FROM THE AREA ALLOWING A DRY 
SLOT TO CONTINUE TO SURGE ACROSS THE REGION. HENCE...IT APPEARS THAT 
THE PRECIP THREAT WILL HAVE ENDED TUE EVENING. TIME SECTIONS 
INDICATE THAT LOW LEVELS REMAIN RATHER MOIST...SO MOSTLY CLOUDY 
CONDITIONS WILL ONLY GRADUALLY GIVE WAY TO PARTLY CLOUDY CONDITIONS 
TUE NIGHT. THERE IS SOME MODEL QPF RESPONSE IN THE SW MOUNTAINS LATE 
TUE NIGHT DUE TO UPSLOPE...SO WILL HAVE SOME CHC TYPE POPS THERE. 
THERMAL PROFILES INDICATE THAT ANY PRECIP WOULD BE LIGHT SNOW 
SHOWERS. AS AN INTENSE UPPER LOW TRACKS INTO THE EASTERN GREAT LAKES 
ON WED...A SHORT WAVE RIDGE IS FORECAST TO BUILD ACROSS THE AREA 
WHICH SHOULD PRODUCE MOSTLY CLEAR CONDITIONS AND NEAR NORMAL TEMPS 
EAST OF THE MOUNTAINS ...ALSO DUE IN PART TO DOWNSLOPING WINDS. 
MOISTURE/CLOUDS WILL INCREASE OVER THE MOUNTAINS BY LATE IN THE DAY 
AS AN UPPER TROUGH APPROACHES. SOME SCT RAIN/SNOW SHOWERS MAY 
DEVELOP BY LATE WED ALONG THE TENNESSEE BORDER COUNTIES. PROFILES 
CONTINUE TO MOISTEN AND COOL OVER THE MOUNTAINS WED NIGHT WITH THE 
WINDS TURING MORE NW. THIS COMBINATION ALONG WITH SOME UPPER AIR 
SUPPORT IS EXPECTED TO PRODUCE NUMEROUS SNOW SHOWERS ACROSS THE 
MOUNTAINS...ESPECIALLY IN THE FAVORED UPSLOPE AREAS. AT LEAST SCT NW 
FLOW SNOW SHOWERS WILL CONTINUE THROUGH THU AS WINDS AND MOISTURE 
REMAIN FAVORABLE...THOUGH COVERAGE IS EXPECTED TO DECREASE THROUGH 
THE DAY THU. SNOW TOTALS OVER THE MOUNTAINS FOR WED NIGHT AND THU 
SHOULD BE IN THE 1 TO 3 INCH RANGE. STAYED CLOSE TO THE METMOS FOR 
TEMPS THROUGH WED NIGHT. FOR THU...USED OUR LOW LEVEL THICKNESS 
SCHEME WHICH YIELDED TEMPS BELOW GMOS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 230 PM EST MONDAY...THE DEEP LOW PRESSURE SYSTEM OVER THE NE 
U.S. ON FRI WILL MOVE OFFSHORE...BUT WITH ADDITIONAL PIECES OF 
SHORTWAVE ENERGY MOVING SWD THROUGH THE CENTRAL AND ERN CONUS TO 
MAINTAIN THE UPPER TROUGH OVER THE AREA. AT LOW LEVELS...ENOUGH 
UPSTREAM MOISTURE WILL PERSIST IN THE COLD NW FLOW TO KEEP SCATTERED 
UPSLOPE SNOW SHOWERS GOING ACROSS THE WRN NC MTNS THROUGH FRIDAY. 
MEANWHILE...THE STRONGEST UPSTREAM SHORTWAVE WILL DIG OVER THE LOWER 
MS RIVER VALLEY...WITH THIS FEATURE LIKELY CROSSING THE EXTREME 
SOUTHERN APPALACHIANS AND ADJACENT FOOTHILLS AND PIEDMONT SOMETIME 
ON SAT. THE ECMWF REMAINS THE MOST VIGOROUS WITH THIS WAVE...BRIEFLY 
CLOSING IT OFF ON SAT...BUT THE GFS/CMC ARE ALSO EXHIBITING BETTER 
TROUGHINESS AND MOISTURE WITH THE WAVE. EVEN THE LESS AMPLIFED 
MODELS APPEAR TO HAVE A FAIRLY POTENT VORT LOBE CROSSING THE 
REGION...AND 850 TO 500 MB LAPSE RATES UP TO 6.5 DEG C/KM MAY 
SUPPORT ISOLD TO SCT SNOW SHOWERS EAST OF THE MTNS SAT. POPS HAVE 
BEEN ADJUSTED UP SLIGHTLY FROM THE PREVIOUS FORECAST.

A RETURN TO NW FLOW UPSLOPE MOISTURE WILL YIELD ADDITIONAL LIGHT MTN 
SNOW SHOWER ACCUMS INTO SUNDAY AS THE UPPER TROUGH AXIS BECOMES 
REINFORCED BY ADDITIONAL SHORTWAVE ENERGY. BETTER DRYING SHOULD THEN 
SET IN THROUGH MON AS HIGH PRESSURE BUILDS IN FROM THE WEST. WILL 
CONTINUE TO FEATURE MINS 5 TO 10 DEGREES BELOW NORMAL...WITH MAXES 
10 TO 15 DEGREES BELOW NORMAL...THROUGH THE PERIOD.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
AT KCLT...WINDS WILL REMAIN BETWEEN 070 TO 060 DEGREES AND 8-14 KTS 
OVERNIGHT AND THROUGH THE EARLY AFTERNOON. WINDS SHOULD BACK TO 
AROUND 300 DEGREES AND DECREASE TO LESS THAN 5 KTS WITH THE PASSAGE 
OF A COLD FRONT BETWEEN 18Z TO 21Z. THE FORECAST CHALLENGE WILL BE 
THE TIMING OF MVFR CLOUDS...MADE MORE DIFFICULT BY EXPANSIVE CIRRUS 
CLOUDS...EXPECTED TO ARRIVE AROUND 6Z. CLOUD BASED SHOULD LOWER TO 
IFR BY 12Z AND WILL LIKELY REMAIN IFR UNTIL DRIER AIR ARRIVE IN THE 
FINAL HOURS OF THIS TAF PACKAGE. IN ADDITION...VIS MAY FALL TO IFR 
BETWEEN 18Z TO 21Z WITH THE GREATEST RAINFALL RATES AND CHC FOR TSRA.

ELSEWHERE...MVFR CLOUDS HAVE STARTED TO SPREAD ACROSS THE UPSTATE OF 
SC AND NC MTNS. ALL WESTERN CAROLINA TAF SITES SHOULD REACH MVFR 
THIS EVENING...KHKY MAY NOT SEE MVFR UNTIL LATE TONIGHT. ALL SITES 
WILL SEE CLOUD BASES LOWER TO IFR AROUND SUNRISE WITH THE ARRIVAL OF 
DEEP MOISTURE AND LLVL LIFT. IFR CEILINGS AND POSSIBLY VIS WILL 
CONTINUE THROUGH MID DAY. MODELS INDICATE A DRY SLOT WILL PUSH 
ACROSS THE UPPER SAVANNAH RIVER VALLEY ANS WESTERN NC MTNS AROUND 
MID DAY...REACHING THE PIEDMONT BY LATE AFTERNOON. KHKY MAY SEE MVFR 
RESTRICTIONS DEVELOP AROUND 22Z AND CONTINUE THROUGH THE REMAINDER 
OF THE TAF PERIOD.
  
OUTLOOK...CLEARING SKIES ARE IN STORE TUESDAY NIGHT WITH VFR 
EXPECTED THROUGH THURSDAY EAST OF THE MOUNTAINS. SOME POTENTIAL FOR 
MVFR ACROSS THE NC MTNS WITH SNOW SHOWERS MID TO LATE WEEK.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z 
KCLT       HIGH  97%     HIGH  91%     HIGH  83%     HIGH  94%     
KGSP       HIGH  92%     HIGH  94%     HIGH  82%     HIGH  88%     
KAVL       HIGH  95%     HIGH  97%     HIGH  96%     MED   74%     
KHKY       HIGH 100%     HIGH  91%     HIGH  91%     HIGH  90%     
KGMU       HIGH  84%     HIGH  94%     HIGH  82%     HIGH  88%     
KAND       HIGH  85%     HIGH  85%     HIGH  95%     HIGH  90%     

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 UNTIL 9 AM EST TUESDAY FOR NCZ033-
     048>050-052-053-064-065-501-503-505-507-509.
     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO 6 PM EST TUESDAY 
     FOR NCZ033-048>052-058-059.
     WIND ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EST TUESDAY FOR 
     NCZ033-048>052-058-059.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...NED/WIMBERLEY
SHORT TERM...LG
LONG TERM...HG
AVIATION...NED