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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
929 PM EST SUN DEC 21 2014

.SYNOPSIS...
A MOIST AIR MASS WILL REMAIN ACROSS THE REGION BEFORE A COLD FRONT 
CROSSES EAST ON WEDNESDAY. DRY CANADIAN HIGH PRESSURE WILL BUILD IN 
THURSDAY AND PERSIST INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 920 PM...RAIN IS GRADUALLY FILLING IN ACROSS THE SC MIDLANDS 
AND LOWER PIEDMONT AS FORCING IS INCREASING IN RESPONSE TO UPPER AIR 
SPEED MAX LIFTING OUT OF THE LOWER MISS VALLEY. BASED UPON CURRENT 
RADAR/OBSERVATIONAL TRENDS...IT/S BECOMING MORE CLEAR THAT PRECIP 
WILL PRIMARILY AFFECT THE EASTERN HALF OF THE FORECAST AREA...AND 
POPS HAVE BEEN SCALED BACK TO CHANCE ACROSS MUCH OF THE WESTERN 
THIRD OF THE FORECAST AREA. THIS IS GOOD NEWS REGARDING THE 
POTENTIAL FOR EASTERN ESCARPMENT/NORTHERN NC MTN FREEZING 
PRECIP...AS IT/S APPEARING MORE LIKELY THAT A COOLING EASTERLY 
UPSLOPE FLOW WILL MAKE IT DIFFICULT TO DISLODGE THE SUB-FREEZING 
TEMPS WHERE THEY CURRENTLY EXIST. WE STILL CANNOT RULE OUT SOME 
-FZRA OR FZDZ...ESPECIALLY ACROSS AVERY COUNTY...SO THE SPECIAL 
WEATHER STATEMENT WILL STAND AS IS. OTHERWISE...THE 00Z NAM HAS 
PICKED UP ON THE DRIER TREND SUGGESTED BY THE LATEST OBSERVATIONAL 
DATA...SO QPF HAS BEEN LOWERED IN ALL AREAS THROUGH THE NIGHT...AS 
EVEN AREAS THAT MEASURE WILL LIKELY SEE AROUND A TENTH OF AN INCH 
OR LESS. 
 
AS OF 650 PM...-RA HAS BEEN A BIT SLOWER TO MATERIALIZE THAN 
PREVIOUSLY ANTICIPATED...BUT IS BEGINNING TO GRADUALLY FILL IN 
ACROSS THE LOWER SC PIEDMONT/MIDLANDS AND SRN/CTRL GA. POPS HAVE 
BEEN MAINTAINED AT PREVIOUS LEVELS (CATEGORICAL ACROSS THE SOUTHEAST 
THIRD...TAPERING TO CHANCE ALONG THE TENN BORDER)...BUT THE ONSET 
HAS BEEN DELAYED A COUPLE OF HOURS. OTHERWISE...THE MAIN CONCERN 
WILL REVOLVE AROUND THE POTENTIAL FOR -FZRA OR -FZDZ ACROSS THE 
NORTHERN MTNS LATER TONIGHT. IT APPEARS THE PRIMARY PROBLEM AREA 
WILL ESSENTIALLY BE AVERY COUNTY...WHERE POCKETS OF FREEZING TEMPS 
ARE CURRENTLY OBSERVED...AND AN INCREASING EASTERLY UPSLOPE FLOW 
WILL LIKELY PROVIDE ENOUGH OF A COOLING MECHANISM TO MAKE IT 
DIFFICULT TO DISLODGE THAT COOL AIR OVERNIGHT. THE AREA OF FREEZING 
RAIN HAS BEEN INCREASED IN THE GRIDS. HOWEVER...QPF WILL STILL BE 
PROBLEMATIC...AS IT/S NO SLAM DUNK THAT THESE AREAS WILL EVEN SEE 
MEASURABLE PRECIP. THEREFORE...DO NOT PLAN TO HOIST ANY ADVISORY 
ATTM...BUT WILL ISSUE AN SPS TO MENTION THE POTENTIAL FOR A VERY 
LIGHT GLAZE...PRIMARILY ON ELEVATED SURFACES.  

AS OF 230 PM...THE STRATUS DECK CONTINUES TO ERODE SLOWLY ACRS THE 
MTNS AND LOWER PIEDMONT THIS AFTN...RESULTING IN SLIGHTLY WARMER 
TEMPS UNDER MORE SUNSHINE. MOST THE AREA IS STILL OVERCAST OR MOSTLY 
CLOUDY...WITH TEMPS IN THE 40S TO LWR 50S.

GUIDANCE IN GOOD AGREEMENT ON A DIGGING TROF TO THE WEST AND A 
BUILDING RIDGE ALONG THE EAST COAST TONIGHT THRU MONDAY. SHORTWAVE 
ENERGY WILL RIDE FROM SW TO NE THRU THE FLOW ATOP THE SOUTHEAST 
STATES...INDUCING A WEAK WAVE ALONG A COASTAL FRONT OFF THE SC COAST 
ON MONDAY. INCREASING SOUTHERLY UPGLIDE AND 850 MB WAA FLOW ATOP THE 
CWFA. POPS QUICKLY RAMP UP TO CATEGORICAL ACRS THE SOUTHERN HALF OF 
THE CWFA...AND LIKELY TO THE NORTH BY LATE EVENING. THE COVERAGE 
WILL BE AIDED BY SOME DEEP LAYER Q-VECTOR CONVERGENCE WITHIN THE 
SWLY MID-UPR FLOW. HOWEVER...THE MOISTURE DEPTH WILL BE FAIRLY 
SHALLOW...AND FORCING OVERALL WEAK. SO QPF AMOUNTS SHUD BE GENERALLY 
A FEW HUNDREDTHS TO A TENTH OF AN INCH. ALTHO...A TENTH TO QUARTER 
INCH POSSIBLE AROUND THE CHARLOTTE METRO AREA. ONE THING TO MENTION 
IS THAT THERMAL PROFILES ARE MARGINAL FOR SOME FREEZING RAIN AND 
SLEET ACRS THE NRN MTNS...MAINLY AVERY COUNTY. THE 12Z NAM AND 
LATEST RAP KEEP THINGS JUST ABOVE FREEZING. I WOULDN/T BE SURPRISED 
IF A FEW SPOTS NEAR THE EASTERLY UPSLOPE AREAS IN AVERY/CALDWELL MAY 
HAVE BRIEF FZRA/DZ TOWARD DAYBREAK MONDAY. HOWEVER...CONFIDENCE IS 
JUST NOT HIGH ENUF TO ISSUE A FREEZING RAIN ADVISORY AT THIS TIME. 
IF THE 18Z NAM COMES IN COLDER...OR IF TRENDS SEEM TO WARRANT 
IT...THE EVENING SHIFT MAY WANT TO ISSUE ONE OR AN SPS. 
OTHERWISE...IT SHUD BE JUST A COLD RAIN WITH TEMPS IN THE 30S TO LWR 
40S.

ON MONDAY...THE MID LVLS DRY OUT...AND THE BETTER FORCING EXITS TO 
THE EAST. HOWEVER...A WEDGE IS EXPECTED TO REMAIN...WITH LLVL 
UPGLIDE CONTINUING WITHIN SWLY FLOW. THIS LOOKS LIKE A GOOD SETUP 
FOR AREAS OF -DZ PERSISTING...ALSO KEEPING TEMPS DOWN. GOING CLOSE 
TO THE RAW MODEL TEMPS FOR HIGHS...AND KEEPING A CHC OF -RA AND DZ 
THRU THE DAY. HIGHS WILL LIKELY STRUGGLE TO GET INTO THE 40S ACRS 
THE I-40 CORRIDOR...AND ONLY THE MID TO UPR 40S ELSEWHERE.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM EST SUNDAY...MON NIGHT THROUGH TUESDAY NIGHT...LATEST 
12Z MODELS CONTINUE TO INDICATE THAT SURFACE COLD AIR DAMMING WEDGE 
WILL CONTINUE ACROSS THE AREA AS 1030MB HIGH WILL REMAIN ANCHORED 
OVER THE NE. MEANWHILE...STRONG SSWLY FLOW ALOFT DEVELOPS ACROSS THE 
SE BY TUE AS A DEEP UPPER TROUGH MOVES EAST ACROSS THE CENTRAL CONUS 
WHILE AN UPPER RIDGE AMPLIFIES OVER THE WESTERN ATLANTIC. THIS WILL 
LEAD TO INCREASING 290K ISENTROPIC LIFT/ATLANTIC MOISTURE ADVECTION 
OVER OUR CWA THRU TUESDAY. HENCE...HAVE CARRIED CHANCE POPS FOR 
LIGHT RAIN WITH DRIZZLE MON NIGHT INTO TUE MORNING...RAMPING UP INTO 
THE CATEGORICAL POPS WITH STEADY RAIN TOWARDS TUE NIGHT. WITH 
ONGOING PRECIP WITHIN THE CAD...AFTERNOON TEMPS ON TUE WILL RUN 7-10 
DEGREES BELOW NORMAL OVER THE PIEDMONT WITH 3-5 DEGREES BELOW OVER 
THE WESTERN NC MTNS. 

WEDNESDAY...THE UPPER TROUGH OVER THE MISSISSIPPI VALLEY WILL 
ADVANCE EASTWARD...BECOMING POSITIVELY TILED AS IT PUSHES THROUGH 
THE EASTERN CONUS. THIS WILL LIFT A SURFACE LOW INTO THE OHIO VALLEY 
BY 18Z...PUSHING ITS ASSOCIATED COLD FRONT THROUGH THE FORECAST AREA 
BETWEEN 18Z WED AND 00Z THU. ALTHOUGH THERE WILL BE STRONG LLVL WIND 
SHEAR ALONG AND AHEAD OF THE FRONT...THE BEST UPPER FORCING WILL NOT 
REACH THE AREA UNTIL 00Z THU AND AREAS SBCAPE REGIME WILL BE SHUNTED 
TO THE SOUTH. THEREFORE...HIGH SHEAR LOW CAPE INDUCED SEVERE EVENT 
APPEARS UNIMPRESSIVE AT THIS TIME. HAVE INHERITED A CHANCE OF 
AFTERNOON THUNDER OVER THE WESTERN NC PIEDMONT...PORTIONS OF THE 
UPSTATE SC...NE GEORGIA AND EXTREME WESTERN NC MTN ZONES TO ACCOUNT 
FOR THE PRESENCE OF WEAK ELEVATED BUOYANCY. AS FOR QPF...MODELS 
STILL DEPICT WIDESPREAD CONVECTIVE ACTIVITY ALONG THE GULF COAST/SE 
COAST...WHICH COULD BLOCK DEEP MOISTURE TRANSPORT INTO OUR AREA. 
WITH THE UNCERTAINTY...HAVE GONE WITH THE MODEL CONSENSUS 
QPF...YIELDING 1-2 INCHES ACROSS THE REGION WITH UP TO 3" OVER THE 
BLUE RIDGE ESCARPMENT. CATEGORICAL POPS WERE HIGHLIGHTED THRU 18Z 
WED... QUICKLY RAMPING DOWN TO THE CHANCE RANGE FROM WEST TO EAST 
THRU 00Z THU AS THE FRONT PUSHES TO THE EAST. WITH INCREASING WAA 
FLOW...AFTERNOON TEMPS WILL WARM INTO THE U50S/60S EAST OF THE MTNS 
AND 50S OVER THE MTNS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 200 PM SUNDAY...THE LATE WEEK WILL SEE THE SHARP UPPER TROUGH
PUSH OFF THE EAST COAST...LEAVING QUASI-ZONAL FLOW OVER THE ERN THIRD
OF THE CONUS. DRY HIGH PRESSURE WILL CROSS THE SOUTHEAST BEFORE
HEIGHTS FALL OVER THE MISSISSIPPI VALLEY AS NEXT LOW ROLLS OFF THE
ROCKIES AND ACRS THE GREAT LAKES. DIFFERENCES BETWEEN THE GFS AND EC
ARE MINOR IN TERMS OF SENSIBLE WX CHRISTMAS DAY AND FRIDAY...BOTH
INDICATING NW FLOW PRECIP TAPERING OFF CHRISTMAS MRNG FOLLOWED BY DRY
WX MOST OF FRIDAY. IN COLD ADVECTIVE PATTERN HIGHER ELEVATIONS WILL
LIKELY SEE BREEZY/GUSTY CONDITIONS ON CHRISTMAS. THE COLD FRONT
ASSOCIATED WITH THE GRT LAKES LOW WILL ARRIVE BY FRIDAY NIGHT ALBEIT
WITHOUT MUCH OOMPH...THE GFS PRETTY MUCH WASHING THE FRONT OUT OVER
THE CAROLINAS. THE EC HOWEVER DIVERGES AT THIS POINT...STALLING THE
FRONT ALONG THE COAST AND EVENTUALLY DEVELOPING A COASTAL LOW NEAR
THE OUTER BANKS SUNDAY IN RESPONSE TO A SRN STREAM SHORTWAVE TRAILING
THE FRONT. BOTH THE 21/00Z AND 21/12Z RUNS FEATURE THIS EVOLUTION. SO
WHILE THE GFS WOULD SUGGEST NEXT WEEKEND WILL BE QUIET AND DRY...EC
INDICATES SOME PTYPE ISSUES MAY EXIST SUNDAY WITH WINTRY PARTIAL
THICKNESSES AND THERMAL PROFILES. TEMPS WILL BE AT OR A LITTLE ABOVE
CLIMO FROM THU-SAT...AND BELOW NORMAL SUNDAY IF THE CLOUDS/PRECIP
MATERIALIZE.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
AT KCLT...INCREASING LIFT THROUGH A DEEP LAYER OF THE ATMOSPHERE IS 
RESULTING IN SLOWLY INCREASING COVERAGE OF -RA ACROSS THE SC 
PIEDMONT/MIDLANDS AND CENTRAL GA...WHICH WILL CONTINUE TO EXPAND AS 
IT LIFTS NE THROUGH THE NIGHT. -RA AND MVFR CHANCES WILL INCREASE BY 
THE END OF THE EVENING...WITH -RA AND/OR -DZ CONTINUING THROUGH MUCH 
OF THE MORNING HOURS. FLT CATEGORY WILL GRADUALLY LOWER TO IFR 
DURING THE PRE-DAWN HOURS. ONCE THIS OCCURS...CONDITIONS WILL BE 
SLOW TO IMPROVE...AS COOL AIR WEDGE IS EXPECTED TO REMAIN LOCKED IN 
NEAR THE SURFACE THROUGH MUCH OF THE PERIOD. WINDS SHOULD REMAIN NE 
AT 5-10 KTS THROUGH THE PERIOD. 
 
ELSEWHERE...MVFR CONDITIONS CONTINUE AT MOST TERMINALS THIS 
EVENING...AND THIS IS LIKELY AS HIGH AS CIGS WILL BE OVER THE NEXT 
24 HOURS. INCREASING LIFT THROUGH A DEEP LAYER OF THE ATMOSPHERE IS 
RESULTING IN SLOWLY INCREASING COVERAGE OF -RA ACROSS THE SC 
PIEDMONT/MIDLANDS AND CENTRAL GA...WHICH WILL CONTINUE TO EXPAND AS 
IT LIFTS NE THROUGH THE NIGHT. CHANCES FOR IFR CIGS WILL INCREASE 
ACROSS THE AREA BY 06Z...AND A TEMPO FOR IFR HAS BEEN INCLUDED AT 
ALL TERMINALS AROUND THIS TIME...WITH IFR CIGS EXPECTED TO SETTLE IN 
NO LATER THAN 07Z OR 08Z. ONCE THIS OCCURS...CONDITIONS WILL BE SLOW 
TO IMPROVE...AS COOL AIR WEDGE IS EXPECTED TO REMAIN LOCKED IN NEAR 
THE SURFACE THROUGH MUCH OF THE PERIOD. 
 
OUTLOOK...WITH LOW LEVEL MOISTURE LOCKED IN PLACE...FLT RESTRICTIONS 
OF SOME SORT WILL LINGER THROUGH AT LEAST EARLY TUESDAY. A COLD 
FRONT WILL APPROACH ON TUESDAY FROM THE WEST AND MOVE THROUGH ON 
WED. WIDESPREAD SHOWERS WITH RESTRICTIONS SHOULD ARRIVE TUESDAY 
AFTERNOON AND WILL CONTINUE UNTIL THE FRONT CLEARS THE AREA LATE 
WEDNESDAY. DRY HIGH PRESSURE WILL RETURN LATE WED.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z 
KCLT       HIGH  98%     LOW   48%     MED   63%     HIGH 100%     
KGSP       MED   78%     MED   63%     MED   72%     HIGH 100%     
KAVL       HIGH 100%     HIGH  82%     MED   71%     HIGH 100%     
KHKY       MED   79%     LOW   55%     MED   68%     HIGH 100%     
KGMU       MED   76%     MED   71%     MED   72%     HIGH 100%     
KAND       MED   61%     LOW   44%     HIGH  84%     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...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...SBK
NEAR TERM...ARK/JDL
SHORT TERM...JOH
LONG TERM...WIMBERLEY
AVIATION...JDL

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