Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 131757
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
157 PM EDT SUN APR 13 2014

.SYNOPSIS...
A WARM SOUTHERLY FLOW OF AIR WILL CONTINUE TODAY. MOISTURE AHEAD OF
AN APPROACHING COLD FRONT IS EXPECTED TO OVERSPREAD THE REGION ON
MONDAY...WITH THE FRONT CROSSING THE AREA ON TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1045 AM EDT SUNDAY...LATEST VISIBLE SATELLITE IMAGERY
INDICATES MULTIPLE LAYERS OF CLOUD COVER ACROSS THE REGION AS HIGH
LEVEL CIRRUS STREAMS IN ALOFT WITH THE MEAN UPPER FLOW WHILE CU
DEVELOPS UNDERNEATH.  14Z SPC MESOANALYSIS INDICATES MODEST MU CAPE
BUILDING ACROSS THE EXTREME WESTERN CAROLINAS AND NORTHEAST GA AS
THE BOUNDARY LAYER WARMS LEADING TO CU FIELD DEVELOPMENT.  FURTHER
DESTABILIZATION WILL OCCUR AS HEATING CONTINUES THEREFORE CURRENT
FORECAST OF CU FIELD EXPANSION ACROSS THE ENTIRE REGION THIS
AFTERNOON REMAINS VALID.  TEMPERATURES ACROSS THE REGION ARE WARMING
NICELY WITH MOST SITES REPORTS MID TO UPPER 60S WITH A FEW LOCATIONS
ALREADY IN THE 70S.  ABOVE MENTIONED SKY COVER EXPANSION WILL
INVERSELY IMPACT HEATING TRENDS THROUGH THE AFTERNOON THEREFORE
CURRENT FORECAST MAX TEMPERATURES REMAIN APPROPRIATE.

PREVIOUS DISCUSSION...

AS OF 630 AM...TEMPERATURES ARE LIKELY RANGING CLOSE TO TODAY/S LOW
TEMPERATURE. I WILL UPDATE THE FORECAST TO INDICATE TEMPERATURES
WILL REMAIN NEARLY STEADY OVER THE NEXT HOUR...THE BEGIN TO WARM
UNDER MOSTLY SUNNY CONDITIONS. FORECAST SOUNDINGS AND LATEST
GUIDANCE INDICATES LESS POTENTIAL FOR AFTERNOON WIND GUSTS. LOW END
GUSTS APPEAR POSSIBLE...BUT WINDS SHOULD FAVOR SOUTH-SOUTHWEST WINDS
BETWEEN 8-13 KTS.

AS OF 245 AM...TODAY THROUGH TONIGHT...H5 RIDGING WILL INCREASE
ACROSS THE SOUTHEAST...REMAINING CENTERED OFF THE CAROLINA COAST. AT
THE SFC...HIGH PRESSURE CENTERED OFF THE NEW ENGLAND COAST WILL
REMAINED RIDGED ACROSS THE SOUTHEAST U.S. TO THE WEST...LOW PRESSURE
WILL TRACK NORTHEAST FROM THE CENTRAL CONUS TO THE MID WEST...WITH A
COLD FRONT SLIDING ACROSS THE MISSISSIPPI VALLEY. THIS PATTERN WILL
SUPPORT MILD LLVL THICKNESSES ACROSS THE SOUTHERN APPALACHIAN
REGION...SUPPORTED BY RETURN FLOW. THE COMBINATION OF FEW TO SCT
SHALLOW CU AND MILD LLVL PROFILES WILL SUPPORT HIGH TEMPERATURES
FROM THE MID 70S WITHIN THE MTN VALLEYS...TO AROUND 80 ACROSS THE
FOOTHILLS AND PIEDMONT. LOW LEVEL MOISTURE AND SOUTHERLY FLOW WILL
INCREASE GRADUALLY OVERNIGHT. NAM AND GFS INDICATE THAT ROUNDS OF
LLVL MOISTURE WILL ARRIVE FROM THE ATLANTIC AND GULF REGIONS
TONIGHT. THE COMBINATION OF THE INCREASING LLVL MOISTURE AND UPSLOPE
FLOW MAY YIELD SCT SHRA ACROSS NE GA AND THE SOUTHEAST FACING SLOPES
ALONG THE NC/SC STATE LINE DURING THE PRE DAWN HOURS.
OVERALL...CONDITIONS TONIGHT WILL FEATURE INCREASING SKY COVER WITH
STEADY SOUTH WINDS. TEMPERATURE ARE FORECAST TO RANGE FROM THE L50S
ACROSS THE MTNS TO UPPER 50S ACROSS THE FOOTHILLS AND PIEDMONT.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 310 AM SUNDAY...GUIDANCE REMAINS IN GENERAL AGREEMENT FOR THE
SHORT RANGE...BUT UNFORTUNATELY...SOME SIGNIFICANT DETAIL
DIFFERENCES CONTINUE. A SERIES OF STRONG SHORT WAVES MOVE ACROSS THE
AREA MONDAY AND MONDAY NITE AHEAD OF A DEVELOPING DEEP CENTRAL CONUS
TROF. SLY LOW LEVEL FLOW STRENGTHENS AS THESE WAVES MOVE THRU
BRINGING IN INCREASING AMOUNTS OF DEEP MOISTURE. FORCING AND UPPER
DIVERGENCE IS QUITE STRONG AS WELL. THE NAM SHOWS QUITE A BIT OF
INSTABILITY...ALONG WITH SIGNIFICANT HELICITY AND SHEAR...LATE
MONDAY AFTERNOON INTO THE EVENING AS THIS SYSTEM MOVES THRU. IN
FACT...EHI VALUES APPROACH 1 DURING THE EVENING. THE GFS HAS
SIGNIFICANTLY LESS INSTABILITY AND SHEAR...BUT THEY ARE NOT ABSENT.
THE SREF MEAN SHOWS 500 J/KG MUCAPE MOVING INTO THE UPPER SAVANNAH
RIVER VALLEY WITH AT LEAST 100 J/KG ACROSS THE CWFA. EXPECT
INCREASING SHRA COVERAGE THRU THE DAY AND OVERNIGHT IN THE
INCREASING MOISTURE AND SLY FLOW. A LINE OF TSRA OR MCS LOOKS LIKELY
FOR LATE AFTERNOON/EARLY EVENING AS THE WAVES MOVE THRU. WHILE SVR
STORM THREAT IS THERE...IT IS STILL TOO EARLY TO TELL THE EVENTUAL
OUTCOME OF OF THIS SYSTEM.

THE UPPER TROF SWINGS ACROSS THE AREA TUE OR TUE EVENING. THE TROF
PUSHES A COLD FRONT ACROSS THE AREA DURING THE DAY AS WELL. THE GFS
REMAINS THE FASTEST MDL MOVING THE FRONT TO THE I-77 CORRIDOR BY 12Z
TUE WHILE ALMOST EVERY OTHER MDL HAS THE FRONT OVER THE NC MTNS
ATTM. THIS TIMING HAS SIGNIFICANT IMPACTS ON THE FCST. THE GFS WOULD
SUGGEST ALMOST NO SEVERE STORM THREAT...WHILE THE OTHER MODELS SHOW
A POTENTIALLY SIGNIFICANT THREAT ACROSS AT LEAST THE I-77 CORRIDOR.
AGAIN...THE STRONG SLY FLOW CONTINUES AHEAD OF THE FRONT WITH DEEP
MOISTURE AND STRONG FORCING FROM THE TROF AND UPPER DIVERGENCE.
SIGNIFICANT INSTABILITY CONTINUES AHEAD OF THE FRONT WITH EVEN
HIGHER SHEAR AND HELICITY...ON ALL BUT THE GFS. EHI VALUES RANGE
FROM 1 TO 1.75 FROM WEST TO EAST ALONG AND SOUTH OF I-85 TUE
MORNING. THEREFORE...WILL HAVE TO KEEP AN EYE ON THIS AS THE SYSTEM
APPROACHES. EITHER WAY...BREEZY TO WINDY CONDITIONS ARE EXPECTED.

PRECIP ENDS FROM SW TO NE TUE AFTERNOON AS DRIER AIR MOVES IN BEHIND
THE COLD FRONT. A BRIEF PERIOD OF NW FLOW PRECIP WILL LINGER ACROSS
THE TN BORDER COUNTIES TUE EVENING. THERE COULD EVEN BE SOME HIGH
ELEVATION SNOW...BUT NO ACCUMS ARE EXPECTED. BREEZY TO WINDY
CONDITIONS WILL LINGER THRU THE EVENING AND OVERNIGHT IN THE MTNS.
TEMPS WILL DROP SIGNIFICANTLY TUE NITE AS COLD HIGH PRESSURE BUILDS
IN BEHIND THE FRONT. IN FACT...GUIDANCE HAS TRENDED COLDER WITH A
FREEZE LOOKING MORE LIKELY ACROSS THE NC MTNS AND NRN FOOTHILLS.
ALTHOUGH TEMPS WOULD SUPPORT FROST ACROSS THE REST OF THE NC
FOOTHILLS AND PIEDMONT...AND PORTIONS OF THE UPSTATE AND NE GA...
THE BREEZY CONDITIONS WOULD KEEP FROST FORMATION TO A MINIMUM.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 410 AM SUN...GUIDANCE REMAINS IN GENERAL AGREEMENT THRU THE
MEDIUM RANGE. UPPER FLOW BECOMES SWLY ACROSS THE SERN CONUS AS A
TROF DEVELOPS ACROSS THE PLAINS THRU THU. THE SRN PORTION OF THE
TROF WEAKENS AS IT MOVES EAST AND ENERGY CONSOLIDATES IN A CLOSED
UPPER LOW WHICH MOVES ACROSS THE GREAT LAKES BY SAT. AT THE SFC...
COOL DRY HIGH PRESSURE BUILDS INTO THE AREA IN A DAMMING
CONFIGURATION WED AND REMAINS IN PLACE THU. CLOUDS RETURN ACROSS THE
AREA AS LOW LEVEL MOISTURE MOVES IN ON INCREASING SLY FLOW OVER THE
DAMMING HIGH. HOWEVER...NO PRECIP EXPECTED. LOWS WED NITE WILL BE
AROUND 10 DEGREES BELOW NORMAL...CREATING FROST/FREEZE POTENTIAL
ACROSS MOST OF THE CWFA. HIGHS 10 TO 15 DEGREES BELOW NORMAL WED
MODERATE TO 5 TO 10 DEGREES BELOW NORMAL THU.

THE MOIST SLY FLOW STRENGTHENS AND BRINGS DEEPER MOISTURE IN OVER
THE DAMMING HIGH THU NITE AND FRI. A SCOURING COLD FRONT CROSSES THE
AREA SAT. THEREFORE...HAVE POP INCREASING INTO THE CHC RANGE FRI AND
CONTINUING THRU SAT. TEMPS WARM AS THE AIR MASS MODERATES ENDING THE
FROST/FREEZE THREAT. LOWS A COUPLE OF DEGREES BELOW NORMAL THU NITE
RISE TO AROUND 5 DEGREES ABOVE NORMAL FRI NITE. HIGHS AROUND 10
DEGREES BELOW NORMAL FRI...RISE TO NEAR NORMAL SAT.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE REMAINDER OF THE
AFTERNOON AND EARLY EVENING BEFORE GIVING WAY TO MVFR...AND
EVENTUALLY IFR CIGS BY DAYBREAK MONDAY.  HIGH LEVEL CIRRUS AND A FEW
CU WILL HIGHLIGHT THE TAF THROUGH THIS EVENING WITH SOUTH WINDS
AROUND 10-12KTS WITH AN OCCASIONAL 15KT GUST POSSIBLE.  CIGS WILL
BEGIN TO LOWER TO AROUND 10KFT BY EARLY MORNING BEFORE DEGRADING
FURTHER TO MVFR LEVELS AS ATLANTIC/GULF MOISTURE ADVECTION SPREADS
ENHANCED LOW LEVEL RH ACROSS THE REGION.  DECIDED TO PREVAIL MVFR
CIGS BY 09Z WITH A THREE HOUR TEMPO FOR POSSIBLE IFR THROUGH
DAYBREAK.  WEAK ISENTROPIC ASCENT WARRANTS MENTION OF PROB30 FOR
-SHRA BR NEAR THE END OF THE PERIOD WITH CIGS IMPROVING SLIGHTLY TO
PREVAILING LOW VFR BY AROUND 16Z.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE AS VFR PREVAILS THROUGH MID
MORNING BEFORE INCREASED LOW LEVEL MOISTURE AND ISENTROPIC ASCENT
REGIME OVERSPREAD THE REGION CAUSING CIGS TO LOWER TO MVFR AND
EVENTUALLY IFR AT ALL LOCATIONS WITH THE EXCEPTION OF KHKY TO THE
NORTH WHERE LOW MVFR WILL PREVAIL.  OTHERWISE...HANDLED IFR CIGS
WITH TEMPOS AT THE SC SITES.  LASTLY...INCLUDED PROB30 AT ALL SITES
FOR UPGLIDE -SHRA BR AROUND DAYBREAK AND EVENTUALLY PREVAIL -SHRA BR
AT KAVL AND KAND NEAR THE END OF THE TAF CYCLE.  SOUTHERLY WINDS
WILL REMAIN IN THE 10-12KT RANGE WITH OCCASIONAL GUSTS POSSIBLE
THROUGH THE AFTERNOON WITH GUSTS SUBSIDING AS THE MIXED LAYER
SHRINKS.  WINDS WILL PICKUP YET AGAIN AFTER DAYBREAK MONDAY AT ALL
SITES WITH GUSTS RETURNING AT KHKY.

OUTLOOK...A LOW PRESSURE SYSTEM DEEPENING ACROSS THE CENTRAL AND
SOUTHERN PLAINS WILL CONTINUE PUSHING EAST THROUGH TUESDAY. MOISTURE
AND LIFT ASSOCIATED WITH THIS SYSTEM WILL LIKELY YIELD RESTRICTIVE
CONDITIONS FROM EARLY MON MORNING THROUGH TUESDAY.  DURING THIS TIME
SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL BE LIKELY.  CONDITIONS
WILL THEN IMPROVE THROUGH WEEKS END WITH RESTRICITONS BECOMING
UNLIKELY.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  87%     HIGH  86%
KGSP       HIGH 100%     HIGH 100%     HIGH  91%     HIGH  94%
KAVL       HIGH 100%     HIGH 100%     HIGH  87%     HIGH  88%
KHKY       HIGH 100%     HIGH 100%     HIGH  96%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH  92%     HIGH  95%
KAND       HIGH 100%     HIGH 100%     HIGH  94%     HIGH  97%

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/NED
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CDG






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