Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 270025
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
725 PM EST WED NOV 26 2014

.SYNOPSIS...
AN UPPER LEVEL SYSTEM WILL CROSS WESTERN NORTH CAROLINA EARLY
THURSDAY. DRY HIGH PRESSURE WILL RETURN FRIDAY AND LINGER INTO THE
WEEKEND. EXPECT A COLD FRONT TO SLOWLY CROSS OUR REGION FROM THE
NORTH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 630 PM...CLOUDINESS AND LIGHT PRECIP CONTINUE TO APPROACH FROM
THE WEST...AHEAD OF A SHORT WAVE. A SMALL PATCH OF LIGHT PRECIP HAD
DEVELOPED NEAR THE SOUTH MTNS. THE PRECIP AREA SHOULD MOVE IN FROM
THE WEST THROUGH THE EVENING HOURS...BUT SOME OF IT WILL NOT REACH
THE GROUND INITIALLY. WILL INCREASE THE PRECIP CHANCES OVER NE
GEORGIA AND THE WRN UPSTATE TO ACCT FOR THIS...AND AT THE SAME TIME
WILL MAKE A FEW CHANGES TO INITIALLY LOWER THE PRECIP CHANCES OVER
THE WRN PIEDMONT. EXPECT PRECIP COVERAGE TO CATCH UP WITH THE FCST
BY LATE EVE. COOLING TEMPS SHOULD ALLOW THE PRECIP TO FALL AS SOME
SNOW AT THE HIGH ELEVATIONS OF THE NC MTNS...SO NO CHANGES TO THE
ADVISORY. TEMP/DEWPT TRENDS ARE VARIABLE...SO IT IS HARD TO GET A
HANDLE ON HOW THAT PART OF THE FCST IS WORKING OUT.

REMAINDER OF PREVIOUS DISCUSSION...

THE FORECAST MODELS AGREE FAIRLY WELL IN BRINGING A STRONG BUT
CHANNELED VORTICITY MAXIMUM WITH THIS WAVE THROUGH THE REGION
OVERNIGHT...WITH MOIST NW FLOW DEVELOPING IN IT/S WAKE. THE DEEP
LAYER QG FORCING SHOULD BE MAXIMIZED MAINLY AROUND 06Z TO 09Z...AND
HAVE THE GREATEST IMPACT ACROSS WRN NC. THERE IS ALSO FAIRLY GOOD
CONSENSUS THAT THE THERMAL PROFILES WILL WET BULB DOWN TO SUPPORT
SNOW ACROSS THE MTNS...AND EVEN INTO THE LOWER VALLEYS...DURING THE
EARLY MORNING HOURS. MOISTURE SHOULD BE JUST DEEP ENOUGH TO SUPPORT
SNOW CRYSTAL GROWTH...BUT THAT MAY NOT EVEN BE AN ISSUE IF
CONVECTIVE SHOWERS FORM AS A POOL OF 7 TO 8 DEG C/KM LAPSE RATES
CROSSES THE REGION OVERNIGHT. THIS INSTABILITY...ALONG WITH A +2 PV
UNIT SATURATED GEOSTROPHIC EPV MAX...MAY WELL PERMIT SOME SNOW
SHOWERS TO BREAK CONTAINMENT EAST OF THE BLUE RIDGE EARLY THU
MORNING. BRIEF SNOW SHOWER ACTIVITY WILL THUS BE POSSIBLE ACROSS THE
INTERSTATE 40 CORRIDOR INTO THE PIEDMONT. HOWEVER...THE DURATION OF
THIS ACTIVITY SHOULD BE BRIEF ENOUGH FOR LITTLE TO NO ACCUMULATIONS
TO DEVELOP WITH MINS GENERALLY IN THE MID 30S.

THE PRECIPITATION FOCUS WILL THEN STEADILY SHIFT BACK TO THE WRN NC
MTN COUNTIES NEAR THE TN BORDER THU MORNING AS A MORE TRADITIONAL NW
UPSLOPE FLOW SNOW SITUATION SETS UP. ANTICIPATE THE DEEPEST SFC TO
850 MB MOISTURE THROUGH 18Z...WITH UPSLOPE MOISTURE GRADUALLY WANING
THROUGH THU AFTN. THE CURRENT WINTER WEATHER ADVISORY LOOKS WELL
PLACED. BREEZY TO WINDY CONDITIONS WILL DEVELOP IN THE HIGHER
ELEVATIONS DURING THE PEAK COLD ADVECTION THU...AS THE PRES GRADIENT
TIGHTENS BEHIND THE DEPARTING WAVE. EXPECT CHILLY 30S TO LOWER 40S
MAXES IN THE MTNS...BUT LOWER 50S ARE MORE LIKELY IN THE EVENTUAL
DOWNSLOPE ACROSS THE FOOTHILLS/PIEDMONT.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AT 230 PM EST WEDNESDAY...ON THURSDAY EVENING...A DEAMPLIFYING UPPER
TROUGH AXIS WILL BE NEAR THE EAST COAST...WHILE A RIDGE WILL BE
UPSTREAM NEAR THE WEST COAST. A CHANNELED UPPER VORT LOBE ROUNDING
THE BASE OF THE TROUGH WILL BE OVER CENTRAL NC...MOVING AWAY FROM
OUR AREA. THE UPPER TROUGH WILL CONTINUE TO DEAMPLIFY ON FRIDAY AS
THE TROUGH AXIS MOVES OFF THE EAST COAST...WHILE WEAK SHORTWAVE
ENERGY MOVES ACROSS OUR AREA FROM THE NW. BY SATURDAY A NEARLY ZONAL
FLOW WILL EXIST OVER THE SOUTHERN TIER OF STATE BY SATURDAY.

AT THE SURFACE...SOME LINGERING NW FLOW SNOW SHOWERS WILL PERSIST
ALONG THE TN BORDER THURSDAY NIGHT IN THE PRESSURE GRADIENT BETWEEN
A DEPARTING COASTAL LOW AND HIGH PRESSURE IN THE MS RIVER VALLEY.
ACCUMULATIONS WITH THIS DIMINISHING ACTIVITY WILL BE MINIMAL. THE
HIGH PRESSURE ARRIVES ON FRIDAY...WHEN THE MODELS SUGGEST SOME UPPER
LEVEL CLOUD COVER SPREADING OVER THE MOUNTAINS FORM THE WEST. THIS
CLOUD COVER WILL EXTEND EAST ACROSS MOST OF THE AREA BY FRIDAY
EVENING...GRADUALLY MOVING NORTH OF THE AREA BY LATE SATURDAY.

TEMPERATURES WILL RUN AROUND 12 DEGREES TO SO BELOW NORMAL ON
THURSDAY NIGHT THROUGH FRIDAY NIGHT AS THE COOL HIGH PRESSURE
ARRIVES...DESPITE RISING HEIGHTS ALOFT. BY SATURDAY...HIGH
TEMPERATURES WILL RISE TO WITHIN 3 DEGREES OR SO OF NORMAL AS WARM
ADVECTION SETS UP ON THE BACK SIDE OF THE SURFACE HIGH AND HEIGHTS
ALOFT CONTINUE TO RISE.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 215 PM EST WEDNESDAY...A WEAK UPPER RIDGE AXIS WILL CROSS THE
REGION SAT NIGHT THROUGH SUN...WITH A WEAK POSITIVELY TILTED UPPER
TROUGH PASSING OVERHEAD ON TUE. ANOTHER WEAK UPPER TROUGH IS
FORECAST TO CROSS THE REGION BY WED.

AT THE SURFACE...HIGH PRESSURE CENTERED OVER THE WESTERN ATLANTIC
WILL CONTINUE TO RIDGE WESTWARD INTO THE FORECAST AREA SAT NIGHT
THROUGH AT LEAST MONDAY BRINGING MOSTLY DRY CONDITIONS WITH GOOD WAA
SWLY FLOW TO OUR CWA. MEANWHILE...A SURFACE COLD FRONT EXTENDING
FROM THE GREAT LAKES REGION TO THE WESTERN GULF SAT NIGHT WILL
SLOWLY PUSH SOUTHEASTWARD INTO THE SOUTHERN APPALACHIANS THROUGH MON
NIGHT. HENCE...HAVE INHERITED DRY WEATHER SAT NIGHT AND SUN FOR MOST
LOCATIONS. POPS THEN RAMP UP INTO THE 20/30S OVER THE MTNS ZONES ON
MONDAY AS THE FRONT REACHES THE TN BORDERLINE. THE FRONT WILL THEN
SLIP TROUGH THE FORECAST AREA MON NIGHT WITH A COLD AIR DAMMING
SETTING UP BY TUE AS A CANADIAN HIGH PRESSURE OVER THE GREAT LAKES
REGION SLIDES EAST INTO THE NORTHEAST STATES. POPS REMAIN ON THE LOW
SIDE GIVEN THE LACK OF DEEP MOISTURE/UPPER FORCING. WED...THE NEW
12Z ECMWF INDICATES THAT ANOTHER COLD FRONT WILL APPROACH FROM THE
NW AND CROSSES THE AREA WED NIGHT INTO THU MORNING WHILE THE GFS
KEEPS THE CAD THRU THE PERIOD. GIVE THE UNCERTAINTY...HAVE KEPT THE
POPS IN THE SLIGHT CHANCE RANGE. TEMPERATURES WILL BE AROUND 2-5
DEGREES ABOVE NORMAL SUN/MON AND NEAR NORMAL TUE/WED.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
AT KCLT...VFR THRU THE PERIOD. SOME HIGH BASED STRATOCU WILL LINGER
ACROSS THE PIEDMONT THRU THE MIDDLE PART OF THE EVENING. A DYNAMIC
SHORT WAVE IS EXPECTED TO MOVE THROUGH OVERNIGHT...WITH MAINLY A MID
LEVEL CEILING PER UPSTREAM OBSERVATIONS. MODEL GUIDANCE SHOWS LIGHT
PRECIP ACCOMPANYING THE PASSAGE OF THE SHORT WAVE DURING THE EARLY
MORNING HOURS. THE BETTER CHANCE FOR LIGHT PRECIP WILL BE TO THE N
OF THE TERMINAL. HAVE NOT INCLUDED PRECIP IN THE TAF AT THIS TIME
BECAUSE THE CHANCE IS TOO LOW. IF PRECIP DOES FALL...IT SHOULD BE IN
FORM OF RAIN...BUT A WET SNOW CHANCE WOULD BE NOT FAR TO THE N.
WINDS HAVE BACKED AROUND TO SE TO S AHEAD OF THE SHORT WAVE
FEATURE...AND SHOULD GRADUALLY VEER AROUND TO S OR SW THROUGH THE
REST OF THE MORNING ON THURSDAY. A COLD FRONT SHOULD CROSS THE
REGION IN THE LATE MORNING WHICH WILL BRING THE WIND DIRECTION
AROUND TO NW. TIMING COULD BE AS EARLY AS 13Z AND AS LATE AS 17Z...
SO THE 16Z PASSAGE FROM THE EARLIER TAF WAS KEPT. CLOUDS SHOULD
SCATTER OUT THEN.

ELSEWHERE...VFR THRU THE PERIOD AT MOST TERMINALS. THE BEST CHANCE
FOR A CEILING RESTRICTION WILL BE AT KAVL AND KHKY...WHERE THE MODEL
GUIDANCE SHOWS THE BEST CHANCE FOR PRECIP. SOME OF THE PRECIP COULD
FALL AS WET SNOW. THE CHANCE REMAINS TOO LOW TO INCLUDE AT THIS
TIME...BUT FUTURE AMENDMENTS COULD ADD IT IN IF CONFIDENCE GOES UP.

OUTLOOK...DRY HIGH PRESSURE WILL SET UP OVER THE AREA FRIDAY THROUGH
THE WEEKEND. A COLD FRONT WILL APPROACH FROM THE NORTHWEST EARLY
NEXT WEEK.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH  98%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  95%     HIGH 100%     HIGH 100%
KHKY       HIGH  88%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     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 FROM MIDNIGHT TONIGHT TO NOON EST
     THURSDAY FOR NCZ033-048>052-058-059.
SC...NONE.

&&

$$
SYNOPSIS...DEO
NEAR TERM...HG/PM
SHORT TERM...JAT
LONG TERM...JOH
AVIATION...PM


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