Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 260632
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
132 AM EST WED NOV 26 2014

.SYNOPSIS...
LOW PRESSURE WILL INTENSIFY ALONG A STALLED COLD FRONT OFF THE
ATLANTIC SEABOARD AND MOVE UP THE COAST TODAY. AN UPPER LEVEL SYSTEM
WILL CROSS WESTERN NORTH CAROLINA EARLY THURSDAY. DRY HIGH PRESSURE
WILL RETURN FRIDAY AND LINGER INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 110 AM...FRONTOGENETICALLY FORCED PRECIP EVENT IS WELL UNDER
WAY ACROSS THE FORECAST AREA...PRIMARILY FROM THE BLUE RIDGE EAST.
TEMPS REMAIN VERY WARM BELOW 3000-3500 FEET...SO IT/S GOING TO TAKE
A GOOD PUSH OF COLD AIR ADVECTION BEFORE SNOW LEVELS CAN FALL TO THE
LOWER VALLEY FLOORS OF THE CENTRAL NC MTNS. IF HISTORY IS ANY
GUIDE...IT/S GOING TO BE DIFFICULT FOR THIS TO OCCUR BEFORE THE
FORCING LIFTS NE. IN FACT...THE 00Z GFS...WHICH HAS BEEN MORE
CONSISTENT WITH THIS EVENT THAN THE NAM (AND DOESN/T HAVE QUITE THE
COLD BIAS TENDENCY OF THE NAM DURING WINTER EVENTS AROUND HERE)
SUGGESTS AN ALL-RAIN EVENT BELOW ABOUT 3000 FEET...AND IT/S REALLY
NOT EVEN CLOSE. NEVERTHELESS...WILL ALLOW THE EVENT TO UNFOLD A BIT
MORE BEFORE MAKING ANY RADICAL CHANGES TO THE WINTER WX PRODUCTS.

AS OF 1030 PM...REGIONAL RADAR INDICATED WIDESPREAD RAIN LIFTING
NORTHWEST ACROSS THE FORECAST AREA. THE TIMING AND PLACEMENT OF THE
LINE LINES UP WELL WITH THE CURRENT FORECAST. IN ADDITION...THE 21S
SREF PLUMES UPDATED WITH SLIGHTLY HIGHER AMOUNTS OF SNOWFALL ACROSS
THE NC MTNS. IF CAA WAS ONGOING...IT WOULD BE A GOOD CALL TO
INCREASE SNOWFALL BASED ON SREF AND LATEST NAM AND GFS.
HOWEVER...THIS WILL BE A TOUGH CASE...PROVIDED THAT CAA WILL NOT
OCCUR BEFORE 12Z. NO CHANGES WILL BE MADE TO FORECAST SNOWFALL OR
WSW WITH THIS UPDATE.

AS OF 850 PM...A BROAD BAND OF LIGHT RAIN WAS LIFTING ACROSS THE
PIEDMONT AND THE UPPER SAVANNAH RIVER VALLEY. THIS BAND WILL
CONTINUE TO ADVANCE NW ACROSS THE REGION AS A BAND OF FRONTOGENESIS
PIVOTS ACROSS THE REGION. IN ADDITION...STRONG MID LEVEL FORCING
WILL DEVELOP ACROSS THE SOUTHERN APPALACHIANS LATE TONIGHT. WAVES OF
LIGHT TO MODERATE RAINFALL SHOULD RESULT IN TEMPERATURES FALLING
TOWARD THE WET BULB. AT 1Z...DEWPOINTS RANGE FROM THE MID 40S ACROSS
THE SOUTHERN PIEDMONT TO THE UPPER 20S WITHIN THE FRENCH BROAD
VALLEY AND RIDGES.

BASED ON LATEST MODEL AND ENSEMBLE GUIDANCE...THE POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE NC MTNS APPEARS A LITTLE GREATER. I WILL
UPDATE THE FORECAST TO INDICATE THAT SNOW WILL OCCUR FOR A LONGER
WINDOW DURING THE EARLY MORNING HOURS. BETWEEN 6Z-12Z...A WIDE FIELD
OF Q-VECTOR COVERGENCE WILL TRACK ACROSS THE REGION. FORECAST
SOUNDINGS AT KAVL AND KTNB INDICATE SATURATED CONDITIONS FROM THE BL
TO 20 KFT. THE DEEP FORCING COMBINED WITH A DEEP LAYER OF SNOW
GROWTH SHOULD YIELD DECENT SNOWFALL RATES. I WILL UPDATE THE WSW TO
CHANGE MADISON AND BUNCOMBE COUNTIES FROM AN HIGH ELEVATION ADVISORY
TO A COUNTY WIDE ADVISORY.

AS OF 715 PM...LATEST RADAR INDICATED A BAND OF LIGHT RAIN OR VIRGA
ACROSS THE PIEDMONT...EAST OF CLT. THIS BAND IS PRIMARILY LOCATED
NW OF A BAND OF FRONTOGENESIS. THE NAM INDICATES THAT H7
FRONTOGENESIS WILL LIFT NORTHWARD THIS EVENING...REACHING THE I-85
CORRIDOR BY 3Z. LARGE SCALE LIFT SLIDE ACROSS THE REGION AROUND
SUNRISE...RESULTING IN THE GREATEST PRECIP RATES.

I ADJUST POPS AND TEMPERATURES...BASED ON THE LATEST MOS AND MODEL
RUNS. IT APPEARS THAT ACCUM SN WILL BE GREATER WITHIN THE MTN
VALLEYS...WITH AREAS SEEING AROUND 2 INCHES. THIS UPDATE WILL
INCREASE THE STORM TOTAL SNOWFALL...WITH PRIMARY FOCUS GIVEN TO THE
VALLEY LOCATIONS.

AS OF 225 PM EST...A FEW WINTER WEATHER WARNING/ADVISORY ADJUSTMENTS
ARE BEING MADE. THE WINTER STORM WARNING IS BEING EXPANDED SLIGHTLY
TO ENCOMPASS AVERY/MITCHELL/YANCEY. THE ADVISORY TIER HAS ALSO BEEN
EXPANDED TO THE ERN SLOPES OF THE NRN BLUE RIDGE AND ALSO A BIT
FARTHER INTO THE CENTRAL AND SRN NC MTNS.

WATER VAPOR IMAGERY SHOWS A POSITIVELY TILTED 500 MB TROUGH EMERGING
FROM THE PLAINS. THIS FEATURE WILL BECOME MORE NEUTRALLY TILTED OVER
THE LOWER MS VALLEY TONIGHT AND THEN ACQUIRE A NEGATIVE TILT AS IT
CROSSES THE APPALACHIANS WED AND PHASES BACK INTO THE BROADER TROUGH
TO THE WEST OF THE APPALACHIANS. AT THE SFC...A LOW CENTER
DEVELOPING ALONG THE FL E COAST LATE TODAY WILL MOVE RAPIDLY UP THE
COASTLINE OF THE CAROLINAS TONIGHT. DEEP LAYER FORCING FROM
FRONTOGENESIS WILL LIKELY SET UP INTO FAR INTERIOR PARTS OF THE
CAROLINAS...POSSIBLY OVER THE FOOTHILLS. IN ADDITION...THE BEST
UPPER DIVERGENCE IN THE RIGHT ENTRANCE REGION OF THE 250 MB JET
STREAK WILL CROSS THE FORECAST AREA FROM THE WEST 09Z TO 15Z...WHILE
DEEP LAYER Q VECTOR CONVERGENCE MAXIMIZES WITH THE TROUGH OVER WRN
NC WED MORNING. THESE FEATURES SHOULD COME TOGETHER TO PRODUCE SOME
SOLID 0.5 TO 0.75 INCH LIQUID EQUIVALENT PRECIP TOTALS TONIGHT
THROUGH WED MORNING. MOST MODELS HAVE SLIGHTLY MORE QPF...BUT
COASTAL CONVECTION COULD BE A LIMITING FACTOR IN CAPPING TOTALS.

REGARDING PTYPES...MODEL PROFILES ALL HAVE SOME DEGREE OF A SFC WARM
LAYER ACROSS THE PIEDMONT...FOOTHILLS...AND LOWER MTN VALLEYS.
HOWEVER...THE MOST TROUBLING MODEL TREND IS FAIRLY STRONG 700 MB
FRONTOGENESIS THAT APPEARS TO SET UP OVER THE FOOTHILLS. ALTHOUGH
NON MTN PROFILES LOOK JUST WARM ENOUGH FOR RAIN THROUGHOUT...ANY
HIGHER RATES COULD OVERCOME THE SFC BASED WARM LAYER AND PRODUCE
SNOW SHOWERS AT TIMES OVER THE NC FOOTHILLS AND THE FAR NW
PIEDMONT...AS WELL AS THE LOWER MTN VALLEYS. THE HIGHER TERRAIN
SHOULD BE SOLIDLY SNOW FOR MOST OF THE EVENT. THE EVENTUAL TRACK OF
THE DEEPENING 850 MB LOW CENTER WILL BE CRITICAL. SINCE THE MODELS
HAVE TRENDED JUST WEST OF INTERSTATE 95...THE ASSOCIATED FORCING FOR
RA/SN SHOWERS WILL BE PUSHED WEST INTO THE FOOTHILLS...WITH
CORRESPONDING SLIGHTLY HIGHER QPF/SNOW TOTALS ALONG AND JUST E OF
THE BLUE RIDGE. FOR THIS REASON...AN ERN ESCARPMENT EXPANSION OF THE
WINTER WEATHER ADVISORY HAS BEEN ADDED. THE NRN MTN FORECAST TEETERS
ON WARNING CRITERIA...BUT SINCE AVERY IS ALREADY IN SEE NO REASON TO
NOT ADD YANCEY/MITCHELL FOR SOME 4 PLUS INCH ACCUMULATIONS OVER AT
LEAST THE ERN HALF OF THESE COUNTIES. ADDITIONAL LOW END ADVISORY
NUMBERS ARE EXPECTED A BIT FARTHER SW IN THE MTN...MAINLY AT HIGHER
ELEVATIONS...BUT THE BRIEF DURATION OF THE EVENT AND THE MARGINALLY
COLD TEMPS SHOULD PRECLUDE ANY WARNING AMOUNT/SIGNIFICANT TRAVEL
PROBLEMS THERE.

A LULL IN ACTIVITY IS EXPECTED BETWEEN UPPER WAVES WED AFTN ALONG
WITH BRIEF DEEPER LAYER DRYING. HOWEVER...LOW LEVEL NW FLOW MOISTURE
MAY CONTINUE TO WRING OUT SCATTERED NRN/WRN MTN SNOW SHOWERS WELL
INTO THE AFTN. WILL TRIM MIN AND MAX TEMPS BELOW
GUIDANCE...ESPECIALLY IN NRN SECTIONS...TONIGHT/WED.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AT 230 PM EST TUESDAY...ON WEDNESDAY EVENING AN UPPER TROUGH AXIS
WILL EXTEND FROM HUDSON BAY TO THE EASTERN GULF OF MEXICO. A STRING
CHANNELED VORT LOBE ROUNDING THE BASE OF THE TROUGH WILL BE
APPROACHING THE SOUTHERN APPALACHIANS. THE VORT LOBE CROSSES OUR
AREA EARLY THURSDAY...WHILE THE DEAMPLIFYING TROUGH PROGRESSES TO
THE EASTERN SEABOARD. BY FRIDAY THE UPPER TROUGH MOVES OFF THE EAST
COAST...AND FLOW ALOFT BECOMES MORE ZONAL.

AT THE SURFACE...A WEAKENING LOW WILL MOVE FROM THE LOWER OH RIVER
VALLEY...ACROSS THE SOUTHERN APPALACHIANS ON WEDNESDAY NIGHT.
MOISTURE AHEAD OF THIS SYSTEM WILL MOVE NE ACROSS OUR AREA...
GENERALLY TO THE NW OF INTERSTATE 85. THICKNESS VALUES ARE RATHER
LOW AT THIS TIME...SUPPORTING MAINLY WINTRY PRECIPITATION TO START
WITH IN THE MOUNTAINS. PREVIOUS MODEL RUNS LACKED A WARM NOSE
ALOFT...BUT MORE RECENT RUNS HAVE A BRIEF WARM NOSE AHEAD OF THIS
LOW. THIS COULD RESULT IN SOME BRIEF FREEZING RAIN IN SOME PORTIONS
OF THE SOUTHWEST NC MOUNTAINS WEDNESDAY EVENING...BUT OVERALL...
PRECIPITATION SHOULD BE IN THE FORM OF SNOW IN THE NC
MOUNTAINS...WITH RAIN TO THE EAST. MODEL SOUNDINGS DO LOWER THE
FREEZING LEVEL LATE WEDNESDAY NIGHT AND EARLY THURSDAY ALONG
INTERSTATE 40...TO THE POINT WHERE SNOW MAY MIX IN WITH RAIN...BUT
SURFACE TEMPERATURES AROUND SIX DEGREES BELOW NORMAL ARE ONLY
MARGINALLY SUPPORTIVE OF SNOWFALL ACCUMULATIONS. AT THIS
POINT...MOUNTAIN SNOWFALL ACCUMULATIONS APPEAR TO FALL SHORT OF
ADVISORY CRITERIA.

BEHIND THE SURFACE LOW...SOME LINGERING NW FLOW SNOW SHOWERS WILL
PERSIST AT HIGHER ELEVATIONS INTO THURSDAY...WHILE LOWER ELEVATIONS
OF THE MOUNTAINS CHANGE OVER TO RAIN. THE EVENT IS EXPECTED TO WIND
DOWN QUICKLY THURSDAY EVENING. GUSTY NE WINDS WILL DELIVER ENOUGH
COLD ADVECTION TO OVERCOME DOWNSLOPE WARMING AND BRING TEMPERATURES
TO AROUND 10 DEGREES BELOW NORMAL ON THURSDAY AND THURSDAY NIGHT.
GUSTY WINDS ABATE ON FRIDAY AS A SURFACE HIGH MOVES OVER THE
AREA....WHILE HIGH TEMPERATURES REMAIN ABOUT 10 DEGREES BELOW NORMAL.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 215 PM TUESDAY...QUASI-ZONAL 500 MB FLOW ACRS THE CONUS TO
START OUT THE MEDIUM RANGE 00Z SAT...THEN A GRADUAL
AMPLIFICATION...WITH ONE TROF SWEEPING ACRS THE GREAT LAKES...AND
ANOTHER ENTERING THE WEST COAST OVER THE WEEKEND. UPPER RIDGING WILL
PERSIST ACRS THE SOUTHEAST STATES...ALBEIT FAIRLY FLAT. AT THE
SFC...A MODERATING HIGH PRES WILL SETTLE ACRS THE CAROLINAS...GA AND
FL. WITH PERSISTENT WESTERLY 850 MB AND INCREASING
THICKNESSES...EXPECT TEMPS TO REBOUND FROM A COUPLE CATEGORIES BELOW
NORMAL SATURDAY...TO 2-3 CATEGORIES ABOVE NORMAL BY MONDAY. THE
ECMWF AND GFS CONTINUE TO DISAGREE ON HOW BULLISH A BACKDOOR COLD
FRONT IS IN PUSHING SOUTH THRU THE AREA MONDAY NIGHT THRU TUESDAY.
THE 12Z/25 ECMWF IS STRONGER WITH A SFC HIGH AS IT SLIDES INTO THE
NORTHEAST STATES...AND KEEPS MORE MOISTURE ATOP A WEDGE DURING THE
DAY ON TUESDAY. THE GFS KEEPS THE FRONT AND MOISTURE MAINLY NORTH OF
THE AREA THRU TUESDAY NIGHT. I WENT WITH THE 12Z HPCGUIDE...WHICH
WAS BASED ON ECWMF ENS...WHICH IS NOT AS BULLISH AS THE OP
ECWMF...BUT DOES INCREASE CLOUDINESS AND BRING SLIGHTLY COOLER TEMPS
ON TUESDAY. OTHERWISE...EXPECT GENERALLY CLEAR TO PARTLY CLOUDY
SKIES AND DRY CONDITIONS. SOME SLGT TO LOW-END CHC POPS WILL EXIST
ALONG THE TN BORDER...AS MOISTURE IS LIFTED WITH PERSISTENT WESTERLY
UPSLOPE FLOW...SUNDAY THRU TUESDAY.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...LIGHT TO MODERATE RAIN WILL CONTINUE THROUGH THE OVERNIGHT
HOURS INTO THE MORNING...BEFORE TAPERING OFF BY EARLY AFTERNOON. OBS
SITES TO THE SOUTH OF HAVE ALREADY DEVELOPED IFR/LIFR CIGS...AND
KCLT RECENTLY DETECTED FEW007. THEREFORE...HAVE INCLUDED A TEMPO FOR
IFR CIGS THROUGH 09Z...WITH CATEGORICAL THEREAFTER UNTIL MID-MORNING
OR SO...WITH VFR EXPECTED TO EARLY AFTERNOON. OCCL IFR VISBY WILL
ALSO BE POSSIBLE. OTHERWISE...N/NE WINDS WILL GRADUALLY TURN TOWARD
THE NW AS SURFACE LOW PRESSURE MOVES UP THE CAROLINA COAST. WINDS
MAY EVEN RETURN TO LIGHT SW BY EVENING...IN ADVANCE OF A FAST MOVING
UPPER AIR DISTURBANCE.

ELSEWHERE...LIGHT/MOD RAIN WILL CONTINUE TO OVERSPREAD THE TERMINALS
THROUGHOUT THE EARLY MORNING HOURS...WITH MVFR CONDITIONS EVENTUALLY
DEVELOPING AS THE LOW LEVEL AIR MAS MOISTENS. OCCL IFR CONDITIONS
WILL BE POSSIBLE...ESP AT KAVL...WHERE SOME SNOW MAX MIX IN WITH THE
RAIN TOWARD DAYBREAK. THERE MAY EVEN BE A BRIEF CHANGE OVER TO ALL
SNOW BEFORE THE PRECIP ENDS AT KAVL DURING MID-LATE MORNING. NO SNOW
IS EXPECTED OUTSIDE THE MTNS...AND THE RA/SN MIX HAS BEEN REMOVED
FROM KHKY. CONDITIONS SHOULD IMPROVE TO VFR BY EARLY AFTERNOON AT
THE LATEST.

OUTLOOK...ANOTHER ROUND OF SCATTERED RAIN SHOWERS SOUTH AND
RAIN/SNOW SHOWERS NORTH WILL IMPACT THE AREA WED NIGHT INTO THU
MORNING. A DRY AIR MASS WILL THEN RETURN TO THE AREA THU NIGHT
THROUGH THE WEEKEND.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  86%     MED   77%     HIGH  94%     HIGH 100%
KGSP       MED   77%     HIGH  84%     HIGH  94%     HIGH 100%
KAVL       HIGH  82%     HIGH  88%     HIGH 100%     HIGH 100%
KHKY       HIGH  94%     HIGH  90%     HIGH  97%     HIGH 100%
KGMU       MED   76%     HIGH  80%     HIGH  98%     HIGH 100%
KAND       HIGH  83%     HIGH  81%     HIGH 100%     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...WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR
     NCZ501-503-505.
     WINTER STORM WARNING UNTIL 4 PM EST THIS AFTERNOON FOR NCZ033-
     049-050.
     WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ048-
     051>053-059-063-064.
SC...NONE.

&&

$$
SYNOPSIS...JDL
NEAR TERM...JDL/NED
SHORT TERM...JAT
LONG TERM...ARK
AVIATION...JDL


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