Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 281737
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
137 PM EDT TUE APR 28 2015

.SYNOPSIS...
A WELL ORGANIZED LOW PRESSURE SYSTEM WILL LIFT ACROSS THE DEEP
SOUTH...TRACKING ALONG THE ATLANTIC COAST DURING THE MID WEEK.
ANOTHER CANADIAN AIR MASS WILL SETTLE BACK OVER THE REGION DURING
THE LATE WEEK AND WILL REMAIN INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 135 PM...CLOUDS SLOWLY BEGINNING TO INCREASE FROM THE WEST.
LATEST GUIDANCE AND REGIONAL RADAR SUGGEST PRECIP ONSET TO BE
DELAYED FROM PREV FCST. HAVE TRENDED THESE FEATURES IN LINE WITH
THAT. HIGH TEMPS LOOK TO BE ON TRACK FROM THE PREV UPDATE.

AS OF 1035 AM...FIRST ROUND OF CIRRUS HAS MOVED EAST OF THE AREA
WITH NEXT ROUND ONLY SLOWLY MOVING TOWARD THE AREA FROM THE WEST.
THIS HAS RESULTED...AND WILL CONTINUE TO RESULT...IN QUITE A BIT OF
EXTRA HEATING WITH NEARLY FULL SUN. CURRENT TEMPS ARE WARMER THAN
FORECAST...SO HAVE RAISED HIGHS A COUPLE OF DEGREES ACROSS THE
BOARD. DID NOT WANT TO GO TOO HIGH AS CLOUDS SHOULD STILL INCREASE
THRU THE AFTERNOON...EVEN IF NOT AS FAST AS EXPECTED. OTHERWISE...
GOING FCST ON TRACK WITH ANY SIGNIFICANT PRECIP HOLDING OFF UNTIL
THIS EVENING WHEN MOISTURE AND FORCING ASSOCIATED WITH THE GULF LOW
MOVE IN.

AS OF 9 AM...UPDATING FORECAST TO REMOVE FROST ADV AND TO INCLUDE
LATEST OBS. LOOKS LIKE THERE WILL BE MORE IN THE WAY OF SUNSHINE...
AT LEAST THIS MORNING...WHICH COULD MAKE A DIFFERENCE IN HIGHS THIS
AFTERNOON. DID NOT CHANGE THE MAXES FOR NOW...BUT WILL CHECK AGAIN
LATER. OTHERWISE...GOING FCST ON TRACK.

AS OF 630 AM TUESDAY...ADDITIONAL MINOR TWEAKS TO TEMPS/DEWPOINTS
BASED ON OBS...SOME MOUNTAIN SITES SUCH AS BOONE HAVE ACTUALLY
DIPPED TO FREEZING...AND MID 30S SPREADING A LITTLE FARTHER SOUTH
INTO SOUTHWEST NORTH CAROLINA THAN ORIGINALLY ANTICIPATED. RIGHT NOW
OVERALL AREAL EXTENT OF FROST ADVISORY STILL LOOKS GOOD BUT MAY SEE
ISOLATED PATCHES OF FROST OUTSIDE THE ADVISORY. SHARP CLEARING LINE
IN SKY COVER FROM THE CIRRUS COVERING THE UPSTATE AND HAVE TRIED TO
REFLECT THAT IN GRIDS AS WELL.

AS OF 430 AM TUESDAY...MADE MINOR TWEAKS TO TEMPS/DEWPOINTS BASED ON
OBSERVATIONS AND ALSO ADJUSTED SKY COVER...INCREASED CLOUDS ACROSS
NORTHEAST GEORGIA AND THE UPSTATE BUT KEPT GRIDS CLEAR ACROSS
ESPECIALLY NORTHEAST ZONES. TEMPERATURES ARE BEGINNING TO DROP AS
FORECAST INTO THE 30S AT THE HIGHER ELEVATIONS OF THE MOUNTAINS...
SO HAVE LEFT FROST WORDING ALONE AND NO CHANGES ANTICIPATED WITH THE
FROST ADVISORY.

AS OF 230 AM EDT TUESDAY...THE NEAR TERM BEGINS WITH THE FORECAST
AREA SORT OF BETWEEN SYSTEMS. STRONG UPPER LOW REMAINS OFF THE NEW
ENGLAND COAST BUT WILL CONTINUE TO PUSH EAST AND OUT FARTHER INTO
THE ATLANTIC. BEHIND THIS SYSTEM AND AHEAD OF THE NEXT WE ARE LEFT
IN SPLIT FLOW ALOFT...BUT GENERALLY NORTHWEST...WITH HIGH PRESSURE
OVER THE PLAINS RIDGING TOWARD THE SOUTHEAST. MAIN FEATURE OF
CONCERN FOR THE NEAR TERM IS THE UPPER LOW SPINNING OVER THE
SOUTHERN PLAINS. ASSOCIATED SURFACE LOW IS CURRENTLY LOCATED IN THE
NORTHWEST GULF... WITH CONVECTION SPREADING EAST ALONG THE WARM
FRONT THAT IS ROUGHLY LINED UP WITH THE SOUTHEAST COASTLINE. AS THE
WAVETRAIN SLIDES EAST...SO WILL THE SURFACE LOW...WITH MOISTURE
OVERSPREADING THE SOUTHEAST.

SHOULD BE A PRETTY QUIET DAY TODAY WITH INCREASING HIGH CLOUDINESS
ACROSS THE AREA AHEAD OF THE APPROACHING GULF LOW AND ATTENDANT WARM
FRONT. SHORT TERM MODELS IN DECENT AGREEMENT ON OVERALL PROGRESSION
OF THE SURFACE LOW...TRAVERSING ALONG THE GULF COAST EARLY IN THE
PERIOD BUT THEN SHIFTING NORTHEAST INTO SOUTH GEORGIA TOWARD THE END
OF THE PERIOD. AS THE CIRRUS THICKENS THROUGH THE DAY...EXPECT THAT
THIS WILL KEEP HIGH TEMPERATURES SEVERAL DEGREES BELOW SEASONAL
NORMALS ACROSS THE AREA. EXPECT A REDUCED DIURNAL RANGE...ESPECIALLY
ACROSS THE UPSTATE WHERE CLOUD COVER WILL BE THICKER...WITH LOWS
TONIGHT FAIRLY CLOSE TO SEASONAL NORMALS.

DEFINITELY SOME DIFFERENCES IN VARIOUS HIRES GUIDANCE WHEN IT COMES
TO PRECIPITATION PUSHING INTO THE AREA LATE IN THE PERIOD.
ISENTROPIC UPGLIDE PROGGED TO INCREASE SIGNIFICANTLY ACROSS THE
FORECAST AREA AFTER 00Z WEDNESDAY...BUT NOT ALL GUIDANCE JUMPING ON
THE BANDWAGON OF WIDESPREAD RAIN. FOR EXAMPLE...SPC SSEO GUIDANCE
TAKES THE NORTHERN EXTENT OF THE PRECIPITATION SHIELD AT BEST ONLY
INTO OUR FAR SOUTHERN ZONES /BUT WITH OROGRAPHIC SHOWER ACTIVITY
DEVELOPING OVER THE MOUNTAINS/. GFS MOST PRONOUNCED WITH THIS BUT
OPERATIONAL NAM PLUS NAM NMM/ARW GUIDANCE ARE SIMILAR. SREF AND
ECMWF BOTH DEPICT A LITTLE MORE WIDESPREAD PRECIPITATION ACROSS THE
AREA. THINK IN THE END...AT LEAST FOR THE NEAR-TERM PERIOD...THIS IS
EASILY A HIGH POP-LOW QPF SCENARIO. HAVE DELAYED THE RAMPING UP OF
POPS INITIALLY BUT STILL BRING LIKELY INTO SOUTHWEST ZONES BY THE
END OF THE PERIOD.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AS OF 300 AM TUESDAY...OUT OF THE SHORT RANGE MODELS...THE 0Z GFS
APPEARED THE BEST INITIALIZED WITH THE LARGE MCS NEAR THE
MISSISSIPPI DELTA. THE LARGE CLUSTER IS EXPECTED TO DRIVE SOUTHEAST
ACROSS THE NORTHERN GULF OF MEXICO TODAY. IN THE WAKE OF THE DEEP
CONVECTION...RAINFALL ACROSS THE DEEP SOUTH WILL SLOWLY REDEVELOP
THROUGH TODAY...LIFTING TO THE NORTHEAST THROUGH TONIGHT. GFS AND
NAM INDICATE THAT THE GREATEST LLVL ISENTROPIC LIFT WILL TRACK
ACROSS THE MIDLANDS WEDNESDAY MORNING. HOWEVER...A REGION OF MID
LEVEL Q-VECTOR CONVERGENCE IS FORECAST TO MOVE WEST TO EAST ACROSS
THE CWA BETWEEN 12Z THROUGH 18Z ON WEDNESDAY. IN ADDITION...H85
WINDS ON THE NORTH SIDE OF THE LOW SHOULD PROVIDE UPSLOPE FLOW
DURING THE MORNING HOURS. I WILL CONTINUE TO FORECAST CATEGORICAL
POPS FOR -SHRA...BUT QPF WILL BE LOWERED TO ALIGN WITH LATEST WPC
FORECASTS. THE THICK CLOUD COVER AND RAINFALL WILL LIMIT DIURNAL
HEATING...I WILL FORECAST MID TO UPPER 50S...WITH THE I-40 CORRIDOR
AROUND 60.

WEDNESDAY NIGHT...THE SFC LOW WILL GRADUALLY DEEPEN AS IT TRACK
NORTHEAST OFF THE SOUTHEAST COAST. MODEL TRENDS INDICATE THAT THE
LOW TRACK MAY OCCUR FURTHER EAST OVER THE ATLANTIC. AT THE MID
LEVELS...A H5 TROF AXIS SHOULD RIPPLE ACROSS THE REGION. MOISTURE
AND FORCING APPEAR LIMITED ACROSS THE FORECAST AREA. HOWEVER...I
WILL CONTINUE TO FORECAST CHC POPS...WITH LOWER VALUES OF QPF. MIN
TEMPERATURES ARE FORECAST TO RANGE FROM THE MID TO UPPER 40S.

THURSDAY...A VERY INTERESTING CLOSED LOW SLIDES ACROSS THE SOUTHERN
TO MID APPALACHIANS DURING THE AFTERNOON. THE BULK OF THE SYNOPTIC
SCALE FORCING SHOULD REMAIN NORTH AND NORTHWEST OF THE FORECAST
AREA. AS THE CLOSED LOW APPROACHES THE WESTERN CAROLINAS...LOW LEVEL
LAPSE RATES ARE FORECAST TO INCREASE TO AROUND 8.5C/KM. THE NAM
INDICATES THAT SBCAPE WILL GENERALLY PEAK DURING THE AFTERNOON
BETWEEN 500 TO 800 J/KG. IT APPEARS THAT SHRA WITH LOW TOPPED TSRA
WILL DEVELOP DURING THE AFTERNOON ENVIRONMENT. SPC DAY 3 OUTLOOK
AGREES THAT GENERAL THUNDERSTORMS SHOULD DEVELOP ACROSS THE WESTERN
CAROLINAS AND NE GA. I WILL FORECAST SOLID CHC TO LOW LIKELY ACROSS
THE REGION...HIGHEST POPS ACROSS THE MTNS AND I-40 CORRIDOR. HIGH
TEMPERATURES MAY RANGE FROM THE U50S WITHIN THE MTN VALLEYS TO THE
MID TO UPPER 60S EAST.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 315 AM TUESDAY...MID LEVEL HEIGHTS ACROSS THE FORECAST AREA
WILL BEGIN WITH A L/W TROF ON FRIDAY...BUILDING TO AT 580 DM RIDGE
BY MONDAY. AT THE SFC...CANADIAN HIGH PRESSURE WILL SLIDE ACROSS THE
REGION FRI/SAT...THE RIDGING WILL CONTINUE INTO MONDAY AND HIGH
BECOMES NEARLY STATIONARY OVER THE WESTERN ATLANTIC. TEMPERATURES
WILL MODIFY THROUGH THE PERIOD...BEGINNING WITH SEASONAL
VALUES...REACHING 5 TO 7 DEGREES ABOVE NORMAL BY MONDAY. POPS WILL
REMAIN LIMITED THROUGH THE PERIOD...VALUES DO NOT EXCEED SCHC.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT...MAINLY VFR CONDITIONS THROUGH THE PERIOD. GUIDANCE HAS
SLOWED THE ONSET OF PRECIP AND ANY RESULTING RESTRICTIONS UNTIL NEAR
THE END OF THE NEW TAF PERIOD. THEREFORE...THE TAF HAS SLOWED AS
WELL. INCREASING CIRRUS THRU THE EVENING WITH VFR LOW CLOUDS MOVING
IN TOWARD DAYBREAK. ANY PRECIP SHUD HOLD OFF UNTIL LATE MORNING.
HAVE ONLY GONE WITH A LOW VFR CIG BY THEN AS WELL. SFC FEATURES ARE
NOT AS WELL DEFINED WHICH IS MAKING WIND FORECAST TOUGH. HAVE LIGHT
NLY WIND THIS AFTERNOON BECOMING ENE THIS EVENING...SE TOWARD
DAYBREAK AND SLY BY LATE MORNING.

ELSEWHERE...OVERALL SIMILAR TREND TO KCLT BUT WITH TYPICAL TIMING
DIFFERENCES AND BETTER RESTRICTION CHANCES ACROSS THE SC SITES. HAVE
PRECIP AND MVFR CIGS COMING INTO KGSP/KGMU NEAR DAYBREAK...AND
BEFORE AT KAND. KAND WILL ALSO SEE IFR CIGS AND MVFR VSBY IN SHRA BY
LATE MORNING. KHKY AND KAVL WILL ONLY SEE LOW VFR IN THE DEVELOPING
SHRA AFTER DAYBREAK. VARIABLE WINDS THIS AFTERNOON WILL TURN NELY
AND REMAIN THERE ACROSS THE SC SITES...WHILE THE NC SITES WILL SEE
VARIABLE WIND BECOMING S OR SW.

OUTLOOK...AN AREA OF LOW PRESSURE WILL PUSH ACROSS THE SOUTHEAST
INTO THURSDAY WITH CONTINUED CIG AND VSBY RESTRICTIONS ANTICIPATED.
AN UPPER LEVEL DISTURBANCE APPROACHES FROM THE NORTH LATE THURSDAY
AND FRIDAY WITH A CONTINUATION OF RESTRICTIONS POSSIBLE. DRY HIGH
PRESSURE MOVES IN FOR THE WEEKEND.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-12Z
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       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  91%

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...NED
NEAR TERM...RWH/TDP
SHORT TERM...NED
LONG TERM...NED
AVIATION...RWH


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