Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 271807
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
207 PM EDT SUN JUL 27 2014

.SYNOPSIS...
A COLD FRONT WILL APPROACH THE CAROLINAS LATE TONIGHT AND PUSH EAST
ACROSS THE REGION ON MONDAY. IN ITS WAKE...CANADIAN HIGH PRESSURE
WILL DOMINATE THE SURFACE PATTERN THROUGH MIDWEEK LEADING TO WELL
BELOW NORMAL TEMPERATURES AND PLEASANT CONDITIONS. PRECIPITATION
CHANCES WILL RAMP BACK UP AGAIN ON THURSDAY AND FRIDAY AS ATLANTIC
MOISTURE SPREADS OVER THE REGION AND LOW LEVEL WINDS BECOME MORE
EASTERLY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 145 PM...MULTIPLE SUPERCELLS HAVE DEVELOPED ALONG AND AHEAD OF
THE COLD FRONT ACROSS EASTERN KENTUCKY THIS AFTERNOON. EXPECT
CONVECTION TO CONTINUE TO DEVELOP TOWARD THE SOUTHWEST THROUGH THE
AFTERNOON...LIKELY CONSOLIDATING INTO AN ORGANIZED MCS THAT WILL
APPROACH WESTERN NC BY EARLY EVENING. WITH THAT IN MIND...STILL
EXPECT THE PRIMARY THREAT OVER OUR AREA TO BE DAMAGING DOWNBURST
WINDS...ALTHOUGH WOULD NOT BE SURPRISED TO SEE AN ISOLATED
TORNADO...ESPECIALLY IF THE PRE-FRONTAL/DISCRETE SUPERCELL CURRENTLY
SOUTH OF JKL MANAGES TO HOLD TOGETHER INTO OUR AREA. POPS HAVE BEEN
INCREASED TO 70 PERCENT ACROSS THE NORTHERN MTNS. THE SHORT TERM
MODELS CONTINUE TO DISSIPATE ANY CONVECTION EAST OF THE MTNS THIS
EVENING...PROBABLY DUE TO A DEVELOPING STRONG WESTERLY DOWNSLOPE
FLOW. HOWEVER...STRONG/COLD POOL-DRIVEN CONVECTION OFTEN /DOES NOT
CARE/ ABOUT DOWNSLOPE FLOW...AND SOME OF THE MESOSCALE MODELS ARE
BEGINNING TO PICK UP ON THE POTENTIAL FOR AN MCS TO BLAST THROUGH
THE FHILLS/PIEDMONT OF NC THIS EVENING. THEREFORE...HAVE BEGUN TO
STEP INTO HIGHER POPS EAST OF THE BLUE RIDGE IN NC THIS EVENING.

AS OF 1040 AM...CONVECTIVE COMPLEX HAS MOVED INTO CENTRAL NC AND THE
SC MIDLANDS THIS MORNING...LEAVING THE AREA ESSENTIALLY FREE OF
CONVECTION. OF COURSE...THE MORNING CONVECTION HAS MUDDIED THE
CONVECTIVE PICTURE FOR THIS AFTERNOON...AS EXTENSIVE MID/HIGH CLOUDS
AND RAIN-COOLED AIR HAS OVERTAKEN MUCH OF WESTERN NC. THIS IS
FURTHER COMPLICATED BY THE CONSIDERABLE MORNING CONVECTION
CONTINUING OVER THE OHIO VALLEY AND CENTRAL APPALACHIANS...WHICH IF
IT DOES NOT PUSH AWAY FROM THE MOD RISK AREA SOON IS SERIOUSLY GOING
TO HAMPER THE POTENTIAL FOR ORGANIZED SEVERE CONVECTION TO DEVELOP
UPSTREAM LATER TODAY. HOWEVER...BASED UPON LATEST SATELLITE/RADAR
TRENDS...IT DOES APPEAR THAT MOST OF THIS ACTIVITY AND ASSOCIATED
DEBRIS CLOUD WILL CONTINUE TO SHIFT EAST ACROSS CENTRAL KENTUCKY/
SOUTHERN WV/SOUTHERN VIRGINIA INTO EARLY AFTERNOON. I/D THEREFORE
SAY IT/S A GOOD BET THAT WESTERN NC AND EAST TENN WILL SEE ENOUGH
HEATING TO REALIZE AT LEAST MODERATE LEVELS OF INSTABILITY THIS
AFTERNOON. AS SUCH...CONSIDERING THE APPROACHING FRONTAL ZONE...THE
POTENTIAL OF ESTABLISHMENT OF A DIFF HEATING BOUNDARY THROUGH THE
DAY...AND THE ANOMALOUSLY STRONG LOW-TO-MID LEVEL SHEAR...NE TENN/NW
NC/EXTREME SW VIRGINIA/SOUTHEAST KENTUCKY MAY END UP BEING GROUND
ZERO FOR ORGANIZED DEVELOPMENT OF DEEP CONVECTION LATE THIS
AFTERNOON INTO THE EVENING...WITH DAMAGING WINDS BEING THE PRIMARY
THREAT. POPS WILL BE MAINTAINED AT SOLID CHANCE TO LIKELY NORTH OF
I-40 DURING THIS TIME.

IN ADDITION...CONSIDERING THE AMOUNT OF INSTABILITY EXPECTED...
CANNOT RULE OUT SOME ISLD/SCT DIURNAL CONVECTION DEVELOPING OVER THE
HIGH TERRAIN THIS AFTERNOON...SO SLIGHT/LOW CHANCE POPS HAVE BEEN
EXTENDED SOUTHEAST ACROSS THE HIGH TERRAIN. SLIGHT CHANCE POPS WILL
ALSO BE EXTENDED SOUTH TO THE I-85 CORRIDOR THIS AFTERNOON...WHERE A
DIFFERENTIAL HEATING BOUNDARY SHOULD BECOME ESTABLISHED BETWEEN THE
RAIN-COOLED AIR AND STRONG INSOLATION AREA OVER THE UPSTATE.
(ALTHOUGH THIS WILL BECOME INCREASINGLY DIFFUSE AS THE AIR MASS
RECOVERS ACROSS WESTERN NC).

MAX TEMPS WERE LOWERED ABOUT A CATEGORY ACROSS MUCH OF WESTERN NC IN
LIGHT OF THE CONTINUING CLOUD COVER...WHILE TEMPS LOOK VERY MUCH ON
TRACK TO REACH THE MID-90S ACROSS THE UPSTATE AND NORTHEAST GEORGIA.

AS OF 650 AM...CONVECTION DID DISSIPATE AS IT CROSSED THE MTNS.
HOWEVER...MCV ASSOCIATED WITH THIS CONVECTION IS HELPING KICK OFF
RENEWED CONVECTION ACROSS THE FOOTHILLS INTO THE PIEDMONT. THIS
CONVECTION WILL SWING ACROSS THE PIEDMONT AND EAST OF THE AREA BY
MID MORNING...WITH A FEW TSRA DEVELOPING. ANOTHER ROUND OF
CONVECTION ACROSS KY IS MOVING TOWARD THE AREA ON A SIMILAR
TRAJECTORY. THIS CONVECTION SHUD REACH THE NC MTNS BY MID MORNING
AND THE PIEDMONT AROUND NOON. THIS CONVECTION IS ALREADY SHOWING
SOME DISSIPATING TRENDS...SO WILL HAVE TO SEE IF IT FOLLOWS A
SIMILAR RESOLUTION AND REDEVELOPS AS IT MOVES OUT OF THE MTNS AND
INTO THE FOOTHILLS. HAVE UPDATED THE POPS TO SHOW THESE TRENDS. WILL
HAVE TO SEE IF THIS CONVECTION AND ASSOCIATED DEBRIS CLOUDS AFFECT
HIGHS FOR THE DAY. HAVE KEPT HIGHS AS IS FOR NOW.

AS OF 330 AM...MCS TO THE NW IS WEAKENING AS IT MOVES EAST TOWARD
THE AREA. HOWEVER...THERE IS ENUF ELEVATED INSTABILITY AND FORCING
FOR CONVECTION TO FORM AHEAD OF THIS SYSTEM. EXPECT THIS
CONVECTION...AND THE MCS ITSELF...TO SPREAD INTO THE NC MTNS AND
I-40 CORRIDOR BEFORE DAYBREAK. THE PRECIP THEN DISSIPATES DURING THE
MORNING BEFORE RETURNING FROM THE NW AS CONVECTION DEVELOPS AHEAD OF
A COLD FRONT MOVING IN. THE ATMOS AHEAD OF THE FRONT IS VERY
UNSTABLE AND BECOMES HIGHLY SHEARED AS A LOW LEVEL JET MOVES IN WITH
THIS SYSTEM. ALTHOUGH INSTABILITY WILL BE SIGNIFICANT ACROSS THE
CWFA...THE BEST SHEAR WILL BE ACROSS THE NC MTNS INTO THE I-40
CORRIDOR. ALTHOUGH SPEED SHEAR IS VERY STRONG...THERE IS LITTLE
VEERING OF THE WINDS AS THE LOW LEVEL WINDS DO NOT BACK AHEAD OF THE
COLD FRONT AND REMAIN SWLY. THE FORECAST SOUNDINGS ALSO SHOW LOW
LEVEL CIN...AND THE DEBRIS CLOUDS FROM THE MCS COULD KEEP HEATING
FROM REACHING MAXIMUM POTENTIAL. HOWEVER THIS WILL EASILY BE
OVERCOME WITH THE STRONG FORCING DEVELOPING. THEREFORE...LOOKS LIKE
A DECENT CHC OF SEVERE STORMS WITH DAMAGING WINDS AND LARGE
HAIL...IN EITHER MULTICELL OR SQUALL LINE FORM...DEVELOPING ACROSS
THE NC MTNS INTO THE I-40 CORRIDOR...BUT THE ISOLATED TORNADO
CHC...WHILE THERE...LOOKS LIMITED WITH BETTER CHC TO OUR NORTH. SVR
CHC...AND EVEN CHC OF CONVECTION...WILL DROP OFF QUICKLY ACROSS THE
SRN CWFA AS SHEAR AND FORCING WILL BE LIMITED. WILL UPDATE HWO FOR
THESE CONCERNS. HIGHS TODAY WILL BE ABOVE NORMAL...BUT NOT AS WARM
AS SOME OF THE MOS GUIDANCE. LOWS TONIGHT WILL BE ABOVE NORMAL AS
WELL.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 225 AM EDT SUNDAY...THE SHORT TERM PERIOD INITIALIZES MONDAY
MORNING WITH A STRONG FRONTAL BOUNDARY PUSHING THROUGH THE REGION.
EXPECTING THE BOUNDARY TO BE LAID ALONG OR JUST SOUTH OF INTERSTATE
85 BY AROUND 12Z...THEN QUICKLY PUSH EAST SOUTHEAST INTO THE
MIDLANDS BY NLT 18Z.  00Z NAM/GFS SOLUTIONS ARE IN GOOD AGREEMENT
REGARDING THIS FROPA TIMING WHICH WOULD GREATLY IMPACT CHANCES FOR
ANY ENHANCED CONVECTION ACROSS THE PIEDMONT REGIONS OF NC/SC.  AS A
MATTER OF FACT...LATEST NAM/GFS CONS FORECAST SOUNDINGS INDICATE
SUBSTANTIAL LOW LEVEL INHIBITION IN PLACE ACROSS THE
PIEDMONT...WHICH ANY UPDRAFTS WILL STRUGGLE TO OVERCOME.  THAT
SAID...HAVE LOWERED POPS FOR THE EASTERN TIER OF THE FORECAST AREA
WITH ONLY SLIGHT CHANCE POPS BEING HIGHLIGHTED THROUGH MIDDAY MONDAY
ALONG WITH LINGERING UPSLOPE SHOWERS ALONG THE HIGH TERRAIN.
DESPITE A NARROW WINDOW OF OPPORTUNITY...STILL CANNOT COMPLETELY
RULE OUT SEVERE THUNDERSTORM THREAT LATE MONDAY MORNING AS THERE
WILL BE A MODERATELY UNSTABLE AIRMASS IN PLACE OUT AHEAD OF FRONTAL
FORCING.  THAT SAID...THE OVERALL THREAT DOES LOOK TO BE DIMINISHING
AS THE FROPA HAS SPED UP SIGNIFICANTLY OVER THE LAST FEW MODEL
RUNS.

STRONG NORTHWEST FLOW DOWN THE DESCENDING BRANCH OF ANOMALOUSLY DEEP
UPPER TROF WILL ADVECT A SHALLOW LAYER OF WESTERN GREAT LAKES
MOISTURE INTO THE SOUTHERN/CENTRAL APPS MONDAY NIGHT.  THUS...POPS
WILL RAMP UP YET AGAIN TO SLIGHT CHANCE LEVELS ACROSS THE NC
MOUNTAINS AS SAID MOISTURE POOLS ON THE WESTERN SLOPES OF THE APPS
AND IS LIFTED MECHANICALLY.  POPS WILL REMAIN ELEVATED AT THOSE
LEVELS THROUGH TUESDAY AFTERNOON WITH A DRY FORECAST ELSEWHERE AS
HIGH PRESSURE BUILDS FOR THE REMAINDER OF THE PERIOD.  TEMPERATURES
THROUGH THE SHORT TERM WILL COOL SIGNIFICANTLY BEHIND THE FROPA WITH
HIGHS NEARLY TEN DEGREES BELOW NORMAL FOR SOME LOCATIONS ON TUESDAY
AFTERNOON.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 140 PM EDT SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
THURSDAY WITH BROAD AND DEEP UPPER TROFFING IN PLACE OVER THE
EASTERN CONUS WHILE AN EQUALLY IMPRESSIVE UPPER RIDGE IS IN PLACE
OVER THE WEST. THE LONG RANGE GUIDANCE CONTINUES TO SUGGEST THAT WE
WILL REMAIN IN THIS AMPLIFIED PATTERN INTO THE WEEKEND WITH SOME
AMOUNT OF DEAMPLIFICATION LIKELY OVER THE WEEKEND. COMPARED TO
PREVIOUS FCSTS...ITS LOOKING LESS CERTAIN THAT THE NORTHERN STREAM
UPPER FLOW WILL COMPLETELY CUTOFF THE TROF AND ALLOW A CLOSED LOW TO
DEVELOP OVER THE WEEKEND. THE LATEST GFS ENSEMBLE RUN HAS ABOUT HALF
OF THE MEMBERS COMPLETELY CUTTING THE TROF OFF AND HALF MAINTAINING
SOME DEGREE OF TROFFING.

AT THE SFC...CANADIAN HIGH PRESSURE WILL CONTINUE TO SLIDE
SOUTHEASTWARD AND WEAKEN ON THURS AS BNDRY LYR FLOW REMAINS NLY TO
WEAK AND VRB. BY EARLY FRI...THE MODELS CONTINUE TO VEER THE FLOW
MORE FROM THE EAST TO NE AND MOVE A LARGE PLUME OF DEEPER LYR
MOISTURE OVER THE CWFA FROM THE SOUTHWEST. THIS UPSLOPE POTENTIAL
COUPLED WITH UPPER LVL DIVERGENCE COURTESY OF THE UPPER TROF AND
POSSIBLY THE CLOSED UPPER LOW IF IT ACTUALLY DEVELOPS...WILL IMPROVE
OUR CHANCES FOR WIDESPREAD SHOWERS AND TS FOR THE REST OF THE MEDIUM
RANGE. OTHERWISE...NO SIGNIFICANT CHANGES WERE MADE TO THE
TEMPERATURE FCST WITH VALUES EXPECTED TO REMAIN WELL BELOW NORMAL
FOR LATE JULY/EARLY AUGUST.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
AT KCLT...A PROB30 FOR TSRA HAS BEEN INTRODUCED BTW 03-06Z
TONIGHT...AS THE POTENTIAL FOR ORGANIZED CONVECTION HOLDING TOGETHER
AS IT CROSSES THE MTNS THIS EVENING APPEARS TO BE INCREASING. IN
FACT...WOULD NOT BE SURPRISED IF THE TIMING IS A BIT FASTER THAN
THIS...BUT FEEL THIS IS THE BEST WAY TO EASE INTO IT FROM A FORECAST
PERSPECTIVE. TRENDS WILL BE MONITORED CLOSELY THROUGH THE AFTERNOON
FOR POTENTIAL AMENDMENTS. OTHERWISE...SW WINDS ARE EXPECTED TO
INCREASE ABOVE 10 KTS THIS AFTERNOON...WITH GUSTS IN THE UPPER TEENS
POSSIBLE. A COLD FRONT WILL MOVE QUICKLY ACROSS THE AREA
OVERNIGHT...WITH WINDS TURNING TOWARD THE W/SW BY MID-MORNING.
OTHERWISE...CONDITIONS SHOULD BE VFR.

ELSEWHERE...VCTS HAS BEEN INCLUDED THIS EVENING AT KAVL/KHKY...WITH
A PROB30 FOR TSRA BETWEEN 03 AND 06Z...AS THE POTENTIAL FOR
ORGANIZED CONVECTION HOLDING TOGETHER AS IT CROSSES THE MTNS THIS
EVENING APPEARS TO BE INCREASING. WHILE THE PROBABILITY OF
CONVECTION AFFECTING THE UPSTATE SC TERMINALS IS LOWER...CANNOT RULE
IT OUT THERE EITHER...BUT AM NOT PREPARED TO ADD ANY CONVECTION
MENTION THERE ATTM. OTHERWISE...SW WINDS MAY GUST TO NEAR 20 KTS
THIS AFTERNOON OUTSIDE THE MTNS. WINDS WILL THEN TURN TOWARD THE W
AND NW OVERNIGHT...AS A COLD FRONT PUSHES THROUGH THE AREA. NW GUSTS
IN THE LOWER 20S WILL BE POSSIBLE AT KAVL MONDAY AFTERNOON.
OTHERWISE...CONDITIONS ARE EXPECTED TO BE VFR OUTSIDE OF ANY
CONVECTION...ALTHOUGH A PERIOD OF MVFR CANNOT BE RULED OUT LATE
TONIGHT AT KAVL.

OUTLOOK...DRY CONDITIONS WILL RETURN BY MONDAY AFTERNOON WITH VFR
CONDITIONS EXPECTED TO REMAIN THROUGH MID WEEK. MOISTURE WILL BEGIN
RETURNING BY LATE IN THE WEEK...WITH INCREASING CHANCES FOR LOW
CLOUDS AND PRECIP.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  94%     HIGH  90%
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...CDG
NEAR TERM...JDL/RWH
SHORT TERM...CDG
LONG TERM...JPT
AVIATION...JDL





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