Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 171122
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
622 AM EST WED DEC 17 2014

.SYNOPSIS...
HIGH PRESSURE WILL SPREAD BACK OVER THE REGION TODAY BEHIND A
DEPARTING COLD FRONT. A WEAK WEATHER SYSTEM ALOFT WILL SPREAD CLOUDS
AND PERHAPS SOME SPOTTY LIGHT SHOWERS IN THE MOUNTAINS ON THURSDAY.
ANOTHER LOW WILL DEVELOP TO OUR SOUTHWEST ON FRIDAY AND INCREASE
CHANCES FOR WIDESPREAD PRECIPITATION GOING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 600 AM EST WEDNESDAY...LATEST RADAR TRENDS REMAIN RATHER
UNIMPRESSIVE REGARDING POSSIBLE LIGHT SHRA ACROSS THE NORTHERN MTNS.
THUS POP FCST WILL REMAIN AS IS WHICH FEATURES ALL POPS BEING
REMOVED WITH THE HOUR.  LOW LEVEL STRATUS ACROSS THE MTNS IS STILL
FCST TO SCATTER THROUGH MORNING.  MADE SLIGHT TWEAKS TO TEMPERATURES
AND DEWPOINTS TO REFLECT LATEST OBSERVATIONS.

PREVIOUS DISCUSSION...

AS OF 300 AM EST WEDNESDAY...QUASI ZONAL UPPER FLOW MIGRATING OVER
THE SOUTHEAST WHILE CANADIAN HIGH PRESSURE DIVES SOUTHWARD THROUGH
THE MS RIVER VALLEY INTO THE OH/TN VALLEYS.  MODEST WEST/NORTHWEST
850MB FLOW ALONG THE CENTRAL APPS CONTINUES TO YIELD SCATTERED
SHOWERS ACROSS PORTIONS OF EASTERN KY NORTHWARD INTO WEST VIRGINIA.
ALTHOUGH AMPLE MOISTURE REMAINS FURTHER SOUTH ACROSS PORTIONS OF
WESTERN NC...WEAKER FLOW CONTINUES TO LIMIT COVERAGE.  LATEST
NAM/GFS REMAIN PERSISTENT IN SUGGESTING INCREASING SHOWER COVERAGE
ALONG THE TN LINE NORTH OF INTERSTATE 40 THROUGH MID MORNING.
HOWEVER...HIGH RES GUIDANCE SUCH AS THE HRRR CONTINUES TO BACK OFF.
ALL SAID...WILL KEEP LOW END SLIGHT CHANCE POPS FOR ISOLATED SHOWERS
ACROSS THE NORTHERN MTNS THROUGH 12Z.  FCST DOES FEATURE BRIEF
PERIOD OF FZRA FOR THESE ZONES AS MODEST INVERSION ALOFT SUGGESTS
PRECIP WILL FALL AS LIQUID WITH SOME FREEZING POSSIBLE TOWARD
MORNING LOWS.  NOT EXPECTING ANY SIGNIFICANT IMPACTS BUT CANNOT RULE
OUT A FEW PATCHES OF BLACK ICE.

BEYOND THAT...HIGH PRESSURE WILL PREVAIL ACROSS THE REGION WITH
MOSTLY SUNNY SKIES DOMINATING OVER THE LOW TERRAIN.  DID KEEP
MENTION OF MOSTLY/PARTLY CLOUDY SKIES ACROSS THE HIGH TERRAIN AS
WEAK WESTERLY UPSLOPE FLOW CONTINUES AMONGST SHALLOW MOIST LAYER.
MEANWHILE ANOTHER WEAK UPPER IMPULSE WILL BE SLIDING THROUGH THE
SOUTHERN PLAINS ALLOWING SOME HIGH LEVEL CIRRUS TO MOVE OVER THE
FCST AREA THIS AFTERNOON THROUGH PERIODS END.  DOWNSLOPING FLOW WILL
YIELD NORMAL LEVEL HIGH TEMPERATURES ACROSS THE FOOTHILLS/PIEDMONT
REGIONS WHILE SLIGHTLY BELOW NORMAL HIGHS ARE FCST OVER THE MTNS.
LOWS TONIGHT WILL BE NEAR NORMAL AS ABOVE MENTIONED INCREASING HIGH
LEVEL CIRRUS LIMITS RADIATIONAL COOLING.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
AS OF 325 AM WEDNESDAY...A WEAK SHORT WAVE WILL MOVE THRU THE ZONAL
FLOW ALOFT THU. THERE IS VERY LITTLE DEEP MOISTURE OR FORCING WITH
THIS SYSTEM. CANNOT RULE OUT A FEW SPRINKLES ACROSS THE NC MTNS
WHERE WLY FLOW MAY BE ABLE TO SQUEEZE THEM OUT OF THE MOISTURE.
THERE SHUD BE QUITE A BIT OF CLOUDS ACROSS THE AREA HOWEVER. SHORT
WAVE RIDGING DEVELOPS AHEAD OF THE NEXT WX SYSTEM APPROACHING FROM
THE SW ON FRI. THIS WILL BRING AN INCREASE IN CLOUDS THRU THE DAY
AFTER THE THU NITE CLEARING FROM THE DEPARTING SHORT WAVE. HIGHS
WILL BE NEAR NORMAL BOTH DAYS...WHILE LOWS THU NITE WILL BE A FEW
DEGREES ABOVE NORMAL.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 355 AM WEDNESDAY...GUIDANCE REMAINS IN GOOD AGREEMENT ON THE
OVERALL PATTERN FOR THE WEEKEND STORM SYSTEM...BUT SOME DIFFERENCES
REMAIN REGARDING THE TEMPERATURE PROFILE AND RESULTING P-TYPES. A
SHORT WAVE APPROACHES THE AREA FRI NITE...MOVES ACROSS THE AREA SAT
AND EAST ON SAT NITE. AT THE SFC...A LOW PRESSURE SYSTEM MOVES EAST
ALONG THE GULF COAST WHILE HIGH PRESSURE SETS UP OVER THE AREA IN A
COLD AIR DAMMING CONFIGURATION. PRECIP CHC INCREASES FROM THE SW FRI
NITE AS MOISTURE MOVES IN AHEAD OF THIS SYSTEM...CAT POP DEVELOPS
ALL AREAS SAT AS THE LOW MOVES SOUTH OF THE AREA...WITH POP SLOWLY
TAPERING OFF SAT NITE AND ENDING ON SUN. THE GFS IS WARMER THAN THE
ECMWF...BUT THE ECMWF IS NOT VERY COLD. USING A BLEND OF THESE TWO
MDLS FOR TEMPS AND THICKNESSES RESULTS IN COLDEST TEMPS AND
THICKNESSES ALONG THE NRN TIER OF THE CWFA...POSSIBLY EXTENDING
SOUTH ALONG THE BLUE RIDGE TO THE SC BORDER. EVEN THEN...P-TYPE
SEEMS TO FAVOR A WINTRY MIX FOR THE NRN BLUE RIDGE AND FREEZING RAIN
EAST AND SOUTH OF THERE. RAIN IS THE P-TYPE FOR MOST OF THE CWFA.
CANNOT RULE OUT ADVISORY LEVEL ICE ACCUMS FOR THE NRN MTN LOCATIONS
LATE FRI NITE AND SAT MORN. HAVE GONE WITH RAIN OR SNOW AS PRECIP
COMES TO AN END SAT NITE AND SUN MORN...BUT THIS AND ANY POTENTIAL
ACCUMS ARE MUCH MORE UNCERTAIN. LOWS WILL BE ABOVE NORMAL FRI AND
SAT NITES...WITH HIGHS SAT 10 DEGREES BELOW NORMAL...RISING TO A FEW
DEGREES BELOW NORMAL ON SUN.

GUIDANCE BEGINS TO DIVERGE FOR THE REST OF THE MEDIUM RANGE. A DEEP
TROF DEVELOPS ACROSS THE CENTRAL CONUS...BUT THE ECMWF IS SLOWER AND
DEEPER WITH THE TROF THAN THE GFS. THE GFS ALSO BRINGS SOME WEAK
SHORT WAVE ENERGY ACROSS THE AREA AHEAD OF THE TROF ON MON...WHILE
THE ECMWF DAMPENS THE WAVE SIGNIFICANTLY. AT THE SFC...THE GFS HAS A
WELL DEFINED LOW PRESSURE SYSTEM WELL SOUTH OF THE AREA ACROSS
FLORIDA AND MOVES IN INTO THE ATLANTIC...KEEPING OUR CWFA RELATIVELY
DRY...WHILE THE ECMWF HAS A LESS DEFINED SFC LOW...BUT A STRONGER
BAROCLINIC ZONE CLOSER TO THE CWFA SPREADING PRECIP IN FROM THE
SOUTH. GIVEN THE DISCREPANCIES...HAVE KEPT MON BASICALLY DRY WITH
TEMPS NEAR NORMAL.

PRECIP SPREADS BACK INTO THE AREA TUE AS A FRONTAL SYSTEM ASSOCIATED
WITH THE UPPER TROF MOVES BACK INTO THE AREA FROM THE WEST.
HOWEVER...DETAILS DIFFER ON EXACT TIMING AND THERMAL STRUCTURE.
THEREFORE...HAVE CHC POP SPREADING IN FROM THE WEST TUE. AGAIN...
GIVEN THE DIFFERENCES...USED RAIN/SNOW FOR THE P-TYPE WHICH WOULD
INDICATE SOME SNOW AT ONSET ACROSS THE NC MTNS...BUT THIS IS ALSO
HIGHLY UNCERTAIN. TEMPS TUE NEAR NORMAL.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. ZONAL FLOW
ALOFT AND WEAK HIGH PRESSURE AT THE SURFACE WILL KEEP SKIES CLEAR
THROUGH MORNING WITH LIGHT NORTHERLY FLOW.  MODELS CONTINUE TO HINT
AT WEAK LEE TROF DEVELOPMENT BY MID MORNING CAUSING FLOW TO BACK
NEARLY DUE WEST THROUGH THE AFTERNOON.  KEPT WINDS JUST NORTH OF
WEST UNTIL 02Z WHEN CALMING PREVAILS. SKIES WILL SLOWLY FILL IN THIS
AFTERNOON IN THE MID/UPPER LEVELS AS CIRRUS STREAMS IN ALOFT FROM
UPSTREAM MOISTURE PLUME ASSOCIATED WITH WEAK UPPER WAVE.

ELSEWHERE...VERY SIMILAR TO KCLT ABOVE WITH VFR PREVAILING AT ALL
SITES.  SURFACE WINDS WILL VARY ACROSS THE REGION DUE TO LEE TROF
DEVELOPMENT BY LATE MORNING.  ALL SC SITES WILL BE LIGHT/CALM BEFORE
INCREASING OUT OF THE SW BY MID MORNING.  AS FOR THE NC SITES...KAVL
WILL REMAIN NORTHERLY AT   8-10KTS THROUGH THE PERIOD WITH KHKY
GRADUALLY BACKING WESTERLY BY MID/LATE MORNING DUE TO ABOVE
MENTIONED LEE TROF.  FLOW WILL VEER NORTHERLY AT ALL SITES LATE IN
THE DAY WITH MID/HIGH LEVEL CIRRUS STREAMING IN ALOFT LEADING TO
CIGS AT KAVL NEAR THE END OF THE TAF CYCLE.

OUTLOOK...A WEAK UPPER DISTURBANCE WILL SLIDE THROUGH THE REGION ON
THURSDAY WITH LITTLE/NO IMPACT EXPECTED.  ANOTHER 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 MOUNTAINS/FOOTHILLS AFFECTING BOTH KAVL AND
KAND SATURDAY MORNING.  WINTRY PRECIP IS NOT EXPECTED AT THIS TIME
FOR ANY OTHER TAF SITES.

CONFIDENCE TABLE...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  80%     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       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...NONE.
SC...NONE.

&&

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



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