National Weather Service Raw Text Product

378 
FXUS62 KGSP 252025
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
325 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 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 /21Z MONDAY THROUGH SATURDAY/...
AT KCLT...CIRRUS CIG THIS AFTN WILL BEGIN TO LOWER BY LATE AFTN AS 
ISENTROPIC LIFT OVER COLD SFC WEDGE RAMPS UP. LOW VFR LOOKS TO SET 
IN BY ABOUT 01Z FOLLOWED BY RAPID LOWERING TO IFR CIG WITH ONSET OF 
RAINFALL THAT WILL CONTINUE THROUGH THE END OF THE PERIOD. GUIDANCE 
SUGGESTS MVFR VSBY WILL ACCOMPANY THE RAIN BUT FOG NOT EXPECTED WITH 
NEAR SFC AIR REMAINING DRY. WINDS REMAIN NE TO ENE UNDER THE WEDGE 
GRADUALLY INCREASING IN STRENGTH AS SFC LOW ENTERS OHIO VALLEY. 
APPROACHING COLD FRONT WILL LIKELY SCOUR OUT THE WEDGE...TURN WINDS 
SWLY AND END THE PRECIP...BUT CURRENT TIMING HAS THIS OCCURRING 
AFTER 18Z.

ELSEWHERE...VFR CIGS THIS AFTN WILL LOWER FROM SOUTH TO NORTH AS 
WARM FRONT/ISENTROPIC LIFT INCREASES AHEAD OF APPROACHING SFC LOW. 
FAR SOUTHERN PART OF THE FCST AREA EXPECTED TO SEE MVFR CIG BY 
AROUND SUNSET WHEN PRECIP SHOULD ALSO BEGIN. PRECIP WILL SPREAD 
NORTHWARD ACROSS ALL SITES OVERNIGHT PEAKING IN COVERAGE AROUND 
SUNRISE. RAIN WILL LIKELY LOWER VSBY TO MVFR...AND THOUGH SFC TEMPS 
MAY REMAIN JUST ABOVE FREEZING IN THE MTNS SOME SNOW/SLEET MAY MIX 
WITH THE RAIN THERE LATE TONIGHT. GUIDANCE GIVING FAIRLY STRONG 
SIGNAL OF WIDESPREAD IFR CIGS ACROSS THE AREA FORMING AROUND 09Z. 
THIS IS LIKELY TO LAST UNTIL COLD FRONT WORKS INTO THE REGION FROM 
THE WEST NEAR THE END OF THE PERIOD. KAVL MAY SEE LIFTING TO VFR 
JUST BEFORE 18Z. WINDS WILL REMAIN IN NE QUADRANT AT ALL SITES UNTIL 
THE FRONT MOVES THROUGH...AGAIN THE ONLY SITE AFFECTED IS KAVL.
  
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...

            20-02Z        02-08Z        08-14Z        14-20Z 
KCLT       HIGH 100%     HIGH  96%     HIGH  86%     HIGH  96%     
KGSP       HIGH 100%     HIGH  95%     HIGH  81%     HIGH  96%     
KAVL       HIGH 100%     HIGH  93%     HIGH  88%     HIGH  83%     
KHKY       HIGH 100%     HIGH  95%     HIGH  91%     HIGH  96%     
KGMU       HIGH 100%     HIGH  95%     HIGH  81%     HIGH  96%     
KAND       HIGH  96%     HIGH  95%     MED   79%     HIGH  96%     

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 9 PM THIS EVENING TO 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...WIMBERLEY
SHORT TERM...LG
LONG TERM...HG
AVIATION...WIMBERLEY