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000
FXUS62 KGSP 171804
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
204 PM EDT FRI MAY 17 2013

.SYNOPSIS...
A MID LEVEL DISTURBANCE WILL DRIFT ACROSS THE REGION THIS
WEEKEND... TRIGGEREING SHOWERS AND THUNDERSTORMS THROUGH THE
BEGINNING OF NEXT WEEK. SOUTHERLY FLOW WILL KEEP THE AIRMASS WARM
AND MOIST... AND THE PATTERN WILL REMAIN UNSETTLED UNTIL A FRONTAL
SYSTEM APPROACHES THE WESTERN CAROLINAS LATE NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1005 AM...TEMPERATURES ACROSS THE REGION CONTINUE TO RISE AS A
THIN LAYER OF MID LEVEL CLOUDS ALLOWS FOR MODERATE RADIATIVE
HEATING.  MOST SITES WERE REPORTING TEMPS IN THE UPPER 60S WITH A
FEW SITES BEING SLIGHTLY WARMER IN THE LOWER 70S.  AFTER LOOKING AT
LATEST NEAR TERM MODEL GUIDANCE...LOOKS AS IF GREATEST THREAT FOR
ANY CONVECTIVE ACTIVITY TODAY CONTINUES TO BE ACROSS THE HIGH
TERRAIN OF THE CAROLINAS WERE UPSLOPE FLOW WILL PROVIDE ENOUGH LOW
LEVEL FORCING TO OVERCOME ANY CAPPING INVERSIONS.  FURTHER SOUTH
ACROSS THE PIEDMONT OF SOUTH CAROLINA...FORECAST SOUNDINGS AND HIGH
RES MODEL GUIDANCE TEND TO KEEP CAP INTACT.  THUS...DECIDED TO LOWER
TO SLIGHT CHANCE POPS NEAR AND ALONG THE I85 CORRIDOR. OTHERWISE...
FORECAST LOOKS TO BE ON TRACK AND NO OTHER CHANGES WERE MADE.

REMAINDER OF PREVIOUS DISCUSSION...

PREVIOUS DISCUSSION...A CLOSED LOW OVER THE MID-SOUTH OPENS UP AND
MOVES ALONG THE LOWER OH VALLEY TODAY. LOW LEVEL MOISTURE WILL BE ON
THE INCREASE ACROSS NC THRU THE DAY. THIS LEADS TO MODERATE
INSTABILITY ACROSS THE AREA BY AFTERNOON. HOWEVER...OVER NE GA AND
THE UPSTATE SOUTH OF I-85 A SIGNIFICANT AMOUNT OF CIN REMAINS IN
PLACE. THEREFORE...HAVE BEST PRECIP CHC OVER THE NC MTNS THEN
DECREASES SOUTH AND EAST. HIGHS SHUD BE 5 TO 10 DEGREES ABOVE
NORMAL.

THE NAM CONTINUES TO BE FARTHER SOUTH WITH THE UPPER LOW TONIGHT AS
IT MOVES SLOWLY EASTWARD. THE OTHER GUIDANCE KEEPS THE LOW CLOSER TO
THE OH VALLEY. EVEN WITH THE LOW POSITION...LOW LEVEL SLY FLOW
INCREASES AGAIN OVERNIGHT BRINGING AN INCREASE IN LOW LEVEL MOISTURE
AFTER MIDNIGHT. EXPECT CONVECTION TO EXHIBIT A SOMEWHAT NORMAL
DIURNAL TREND DURING THE EVENING. HOWEVER...PRECIP CHC INCREASES
FROM WEST TO EAST AFTER MIDNIGHT AS THE LOW LEVEL MOISTURE AND
FORCING INCREASE. TSRA WILL BE POSSIBLE AS WELL WITH THE FORCING AND
CONTINUED ELEVATED INSTABILITY. LOWS WILL BE AROUND 5 DEGREES ABOVE
NORMAL.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AT 300 AM EST FRIDAY...ON SATURDAY THE REMAINS OF AN UPPER LOW
TRACKS EAST OVER THE OH RIVER VALLEY IN THE GFS...AND OVER THE TN
RIVER VALLEY IN THE NAM. BOTH MODELS THEN MOVE THE SYSTEM SOUTHEAST
SATURDAY NIGHT...WITH THE GFS DISTURBANCE CROSSING THE CENTRAL
APPALACHIANS...AND THE NAM DISTURBANCE CROSSING NORTH GA. ON SUNDAY
THE GFS SYSTEM MOVES SLOWLY ACROSS THE CAROLINAS...WHILE THE NAM
SYSTEM MOVES EVEN SLOWER INTO THE UPPER SAVANNAH RIVER VALLEY. THE
GFS SYSTEM REACHES THE COAST ON SUNDAY NIGHT.

DEEP MOISTURE AND INSTABILITY WILL INCREASE AS THE REMAINS OF THE
UPPER LOW APPROACH...SUPPORTING INCREASING POPS...GENERALLY GREATER
DURING THE DAYTIME HOURS...BUT WITH OVERNIGHT ACTIVITY AS WELL.
CONVECTION WOULD APPEAR TO FINALLY WANE FROM THE WEST ON SUNDAY
NIGHT... ASSUMING THE GFS TIMING IS CORRECT. WITH A DEEP MOIST
LAYER...DRY AIR WILL NOT BE AVAILABLE FOR EVAPORATIVE COOLING...
LIMITING DOWNDRAFT PATERNAL. CONVECTIVE CELLS COULD PRODUCE HEAVY
RAINFALL...BUT WIND PROFILES SUGGEST CELLS WILL MOVE OFF TO THE
NORTHEAST ON MONDAY...AND MORE SLOWLY TO THE EAST ON SUNDAY...WITH A
WEAK SOUTHERLY UPSLOPE FLOW IN HTE LOWEST LEVELS. HIGH TEMPERATURES
WILL BE NEAR NORMAL...AND LOW TEMPERATURES A COUPLE OF CATEGORIES
ABOVE NORMAL.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AT 300 AM EST FRIDAY...THE ECMWF AND GFS MOVE AN UPPER RIDGE SLOWLY
ACROSS THE SOUTHERN APPALACHIANS FROM MONDAY THROUGH WEDNESDAY...
ALTHOUGH THE GFS SHOWS A WEAKNESS IN THE RIDGE OVER THE CAROLINAS
THAT LINGERS INTO THURSDAY. AN UPPER TROUGH WILL MOVE FROM THE MS
RIVER VALLEY ON WEDNESDAY TO THE OH AND TN VALLEYS BY THURSDAY.

THE SOUTHEAST WILL REMAIN IN A WARM AND MOIST AIR MASS FROM MONDAY
THROUGH THURSDAY...WITH WEAK GULF INFLOW MAINLY TO THE WEST OF THE
APPALACHIANS. DIURNALLY MODULATED POPS WILL BE CARRIED...FAVORING
THE MOUNTAINS FOR THE HIGHEST POPS WITH OROGRAPHIC EFFECTS. MAXIMUM
TEMPERATURES WILL RUN NEAR NORMAL...WITH MINIMUMS A COUPLE OF
CATEGORIES ABOVE NORMAL.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE FIRST HALF OF THE
TAF PERIOD.  SOME AFTERNOON CONVECTION IS EXPECTED OVER THE NC
MOUNTAINS...HOWEVER THIS ACTIVITY SHOULD STAY TO THE WEST OF KCLT.
WINDS FOR THE REMAINDER OF THE DAY WILL STAY LIGHT AND SOUTHERLY.
OTHERWISE...EXPECTING CLOUD COVER TO INCREASE THIS EVENING AS
EASTWARD MOVING UPPER TROUGH CONTINUE TO APPROACH.  THUS...CARRIED
LOW END VFR CIGS THROUGH THE MORNING...THEN LOWERED TO MVFR BY 13Z
AS SHOWER AND THUNDERSTORM ACTIVITY WILL BEING TO INCREASE ACROSS
THE REGION.

ELSEWHERE...EXPECTING CONDITIONS TO STAY AT VFR LEVELS THROUGH THE
EVENING WITH THE ONLY EXCEPTION BEING AT KHKY AS CIGS LOOK TO DROP
JUST AT OR BELOW 3K FEET.  BY DAYBREAK SATURDAY...EXPECTING FLIGHT
CONDITIONS TO LOWER FURTHER AT THE REMAINING SITES TO MVFR LEVELS AS
OVERALL COVERAGE OF SHOWERS AND OR THUNDERSTORMS INCREASES.

OUTLOOK...SHOWER AND THUNDERSTORM COVERAGE...AND ASSOCIATED
RESTRICTIONS...WILL GRADUALLY INCREASE SATURDAY THROUGH MONDAY. FAIR
WEATHER MAY RETURN BY TUESDAY.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  85%     MED   66%
KGSP       MED   63%     HIGH 100%     HIGH  94%     MED   78%
KAVL       LOW   56%     LOW   57%     LOW   55%     MED   65%
KHKY       HIGH 100%     HIGH 100%     HIGH  96%     LOW   46%
KGMU       MED   71%     HIGH 100%     HIGH  94%     MED   65%
KAND       HIGH  85%     HIGH 100%     HIGH  93%     LOW   46%

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...LEV
NEAR TERM...CDG/RWH
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...CDG