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Area Forecast Discussion

337
FXUS62 KGSP 180854
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
354 AM EST THU DEC 18 2014

.SYNOPSIS...
A WEAK WEATHER SYSTEM ALOFT WILL SPREAD CLOUDS OVER THE AREA AND
PERHAPS SOME SPOTTY LIGHT SHOWERS IN THE MOUNTAINS TODAY. A LOW
PRESSURE SYSTEM WILL DEVELOP TO OUR SOUTHWEST ON FRIDAY AND INCREASE
CHANCES FOR WIDESPREAD PRECIPITATION GOING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 230 AM EST THURSDAY...QUASI ZONAL FLOW ALOFT WILL BE DISRUPTED
SLIGHTLY BY AN APPROACHING SHORT WAVE IMPULSE THAT IS CURRENTLY
SLIDING THROUGH THE ARKLATEX.  MOIST UPGLIDE ATOP SOUTHWARD
INTRUDING SFC HIGH PRESSURE CONTINUES TO YIELD LIGHT/MODERATE PRECIP
OVER THE MID MISSISSIPPI RIVER VALLEY.  CLOSER TO HOME...PARTLY
CLOUDY SKIES PREVAIL AS HIGH LEVEL CIRRUS STREAMS IN ALOFT FROM
ABOVE MENTIONED ACTIVITY TO THE WEST.  TEMPERATURES ACROSS THE
REGION CONTINUE TO SLOWLY FALL DIURNALLY AIDED BY LIGHT/CALM
WINDS...DESPITE INCREASING SKY COVER.  INTRODUCED MENTION OF PATCHY
FOG FOR PORTIONS OF THE SAVANNAH RIVER...AND LITTLE TN RIVER VALLEYS
THIS MORNING WITH PERIODS OF FREEZING FOG POSSIBLE IN THE LITTLE TN
VALLEY AS TEMPERATURES REMAIN IN THE UPPER 20S.  WILL MONITOR THE
SITUATION THROUGH MORNING AND ISSUE SPS IF NEEDED.

OTHERWISE...UPPER SHORT WAVE MENTIONED ABOVE WILL CROSS THE
CENTRAL/SOUTHERN APPS THROUGH THE DAY LEADING TO INCREASED/OVERCAST
SKIES FOR THE VAST MAJORITY OF THE FORECAST AREA.  GUIDANCE
CONTINUES TO HINT AT LOW END POPS ALONG THE TN LINE AS SHOWERS
STREAM IN FROM THE WEST AND ARE AIDED BY WEAK UPSLOPING.  KEPT THIS
IN THE FCST FOR THE EARLY AFTERNOON ALONG THE SMOKIES BEFORE
TRANSITIONING UP THE SPINE INTO THE NORTHERN MOUNTAINS BY EARLY
EVENING.  ALL POPS ARE REMOVED BY 01Z LEADING TO A DRY FCST FOR THE
REMAINDER OF THE PERIOD.  SKIES WILL CLEAR OUT ACROSS THE LOW
TERRAIN FROM THE SOUTHWEST AS THE UPPER WAVE AND ASSOCIATED MOISTURE
PLUME EJECT NORTHEAST.  EXPECTING PERSISTENTLY CLOUDY SKIES FOR THE
MOUNTAINS AS LOW LEVEL FLOW VEERS NORTHWESTERLY ALLOWING MOIST
UPSLOPE EFFECTS TO CONTINUE.  TEMPERATURES ACROSS THE REGION WILL
REMAIN NEAR CLIMO THROUGH THE PERIOD.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 325 AM THURSDAY...FRIDAY WILL BE THE CALM BEFORE THE STORM AS
HIGH PRESSURE BUILDS IN FROM THE NW. EXPECT INCREASING CLOUDS AND
HIGHS NEAR TO SLIGHTLY ABOVE NORMAL.

GUIDANCE HAS COME IN WEAKER WITH THE FORCING AND FASTER WITH THE
MOVEMENT ASSOCIATED WITH THE FLAT UPPER WAVE CROSSING THE AREA SAT.
THEY ARE ALSO WEAKER...FARTHER SOUTH AND FASTER WITH THE SFC LOW
PRESSURE SYSTEM MOVING TO THE SOUTH DURING THE DAY. THE SLY H85 FLOW
IS STILL THERE AND VERY MOIST...BUT IT IS WEAKER AS WELL. THE HYBRID
CAD APPEARS TO REMAIN SIMILAR HOWEVER. THEREFORE...ALTHOUGH PRECIP
WILL BECOME WIDESPREAD BY SAT MORN...THE QPF HAS DROPPED
SIGNIFICANTLY. THE THERMAL PROFILES HOWEVER HAVE REMAINED GENERALLY
THE SAME...BRINGING WINTRY PRECIP TO THE MTNS NORTHEAST OF THE
FRENCH BROAD VALLEY AND PORTIONS OF THE I-40 CORRIDOR OUTSIDE OF THE
MTNS. EXPECT LIQUID RAIN SOUTH OF THAT AREA. PRECIP WILL BEGIN WITH
A LITTLE FREEZING RAIN MIXING IN ACROSS THE NRN MTNS...THEN QUICKLY
TRANSITION TO SLEET AND SNOW AS THE COLUMN MOISTENS AND WET BULBS
BELOW ZERO. WWA KICKS IN AFTER DAYBREAK SAT WITH PRECIP BECOMING ALL
LIQUID BY AFTERNOON. WITH THE LOWER QPF EXPECTED...ESPECIALLY ACROSS
THE NRN TIER WHERE THE WINTRY MIX DEVELOPS...EXPECTED ACCUMS HAVE
DIMINISHED AS WELL. NOW EXPECT GENERALLY LESS THAN AN INCH OF SNOW
AND/OR SLEET...LIMITED TO THE NRN MTNS AND BLUE RIDGE. THAT SAID...
ANY CHANGES IN TEMPS OR QPF COULD BRING TOTALS BACK HIGHER. LOWS FRI
NITE WILL BE AROUND 5 DEGREES ABOVE NORMAL...WHILE HIGHS SAT WILL BE
AROUND 10 DEGREES BELOW NORMAL WITH THE CAD AND PRECIP.

WITH THE FASTER MOVEMENT OF THIS SYSTEM...PRECIP TAPERS OFF DURING
THE LATE AFTERNOON AND EVENING SAT...WITH PRECIP ENDING AFTER
MIDNIGHT. WITH TEMP PROFILES REMAINING RELATIVELY WARM...BUT SFC
TEMPS FALLING BACK BELOW FREEZING...THE PRECIP COULD END AS FREEZING
RAIN OR DRIZZLE...ESPECIALLY ACROSS THE NRN MTNS AND BLUE RIDGE...
AND POSSIBLY THE HIGHER ELEVATIONS WEST OF THE FRENCH BROAD VALLEY
AND LOCATIONS NORTH OF HKY. EVEN IF THIS DOES OCCUR...QPF WILL BE
VERY LIGHT WITH NO SIGNIFICANT ICING EXPECTED. LOWS WILL BE NEAR TO
A LITTLE ABOVE NORMAL.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 350 AM THURSDAY...SHORT WAVE RIDGING BUILDS OVER THE AREA
SUNDAY AS A TROF DEVELOPS OVER THE CENTRAL CONUS. SOME SHORT WAVE
ENERGY WILL TRY TO MOVE THRU OR UNDER THE RIDGE AND ACROSS THE AREA
SUNDAY INTO MONDAY AS THE RIDGE AXIS MOVES OFF SHORE AND THE CENTRAL
CONUS TROF CONTINUES TO DEVELOP. A BAROCLINIC ZONE LINGERS NEAR THE
GULF COAST WITH ANOTHER HIGH MOVING INTO A DAMMING CONFIGURATION.
THE SHORT WAVES DEVELOP LOW PRESSURE ALONG THE FRONT AND HELP
DEVELOP SLY LOW LEVEL FLOW BRINGING MOISTURE BACK INTO THE AREA LATE
SUNDAY INTO MONDAY. SFC TEMPS AND THERMAL PROFILES SUGGEST FREEZING
RAIN COULD DEVELOP ACROSS THE NRN MTNS LATE SUN NITE INTO MON MORN.
LIGHT ICE ACCUMS ARE POSSIBLE...BUT MOST OF THE AREA WILL SEE LIQUID
PRECIP. HIGHS SUNDAY AND MONDAY WILL BE A LITTLE BELOW NORMAL WHILE
LOWS WILL BE A LITTLE ABOVE.

TUESDAY AND WEDNESDAY...THE UPPER TROF CONTINUES TO STRENGTHEN WITH
A CLOSED LOW FORMING OVER THE NRN PLAINS. THE ECMWF IS DEEPER WITH
THE TROF...STRONGER WITH THE CLOSED LOW...AND SLOWER WITH THE
MOVEMENT OF THE SHORT WAVES ROTATING AROUND THE LOW AND THE EASTWARD
MOVEMENT OF THE TROF. PRECIP RETURNS FROM WEST TO EAST ACROSS THE
AREA AS A STRONG COLD FRONT AND TRIPLE POINT LOW DEVELOP AND MOVE
ACROSS THE AREA SOMETIME TUE NITE. THERE IS STILL QUITE A BIT OF
UNCERTAINTY WITH THE DETAILS OF THIS SYSTEM...BUT HEAVY RAIN AND
SEVERE STORMS ARE POSSIBLE GIVEN THE STRENGTH OF THE SYSTEM...THE
ASSOCIATED STRONG WIND...AND WEAK INSTABILITY DEVELOPING AHEAD OF
THE TRIPLE POINT LOW. NO SIGNIFICANT WINTRY PRECIP IS EXPECTED AHEAD
OF THIS SYSTEM. HOWEVER...WINDY AND COLD CONDITIONS DEVELOP BEHIND
THE FRONT ON WED...AND COULD LEAD TO A NW FLOW SNOW EVENT. TEMPS
WILL BE ABOVE NORMAL AHEAD OF THE FRONT AND BELOW NORMAL BEHIND.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD.  ALL TAFS INITIALIZE WITH FEW/SCT HIGH LEVEL CIRRUS.  CIRRUS
WILL THICKEN/LOWER THROUGH MORNING WITH MID LEVEL CIGS FEATURED.  AS
WEAK UPPER WAVE SLIDES BY JUST TO THE NORTH ON THURSDAY...EXPECTING
LOW VFR BKN CIGS TO PREVAIL AT ALL SITES BEFORE SCT OUT INTO THE
EVENING.  WINDS OVERNIGHT WILL REMAIN LIGHT AND NORTHERLY WITH
GRADUAL VEERING TO THE NORTHEAST BY MORNING AT ALL SITES ASIDE FOR
KAVL WHERE WINDS REMAIN NORTHERLY THROUGH THE PERIOD.  WINDS WILL
VEER S/SW AND INCREASE TO 4-7KTS BY LATE MORNING LASTING THROUGH THE
AFTERNOON AT ALL OTHER SITES AS WEAK LEE TROF DEVELOPS.  FLOW WILL
THEN WEAKEN AFTER SUNSET WITH BRIEF NORTHERLY WINDS LEADING INTO A
CALM EVENING AMIDST SCATTERING LOW VFR SKIES.

OUTLOOK...A MORE ORGANIZED SYSTEM WILL APPROACH FROM THE WEST FOR
THE START OF THE WEEKEND ONCE AGAIN INCREASING PRECIP/RESTRICTION
CHANCES.  SOME WINTRY PRECIP IS POSSIBLE ACROSS THE NC MTNS AND
FOOTHILLS AFFECTING KAVL/KHKY SATURDAY MORNING. WINTRY PRECIP IS NOT
EXPECTED AT THIS TIME FOR ANY OTHER TAF SITES.

CONFIDENCE TABLE...

            09-15Z        15-21Z        21-03Z        03-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       MED   66%     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...NONE.
SC...NONE.

&&

$$
SYNOPSIS...RWH
NEAR TERM...CDG
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CDG



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