Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 280724
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
324 AM EDT THU APR 28 2016

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA FROM THE WEST THIS EVENING...WITH
HIGH PRESSURE BRIEFLY RETURNING FOR FRIDAY INTO SATURDAY. A LOW
PRESSURE SYSTEM WILL APPROACH FROM THE WEST LATE SATURDAY THROUGH
SUNDAY NIGHT. THE LOW WILL LIFT NORTHEAST ALONG THE COAST EARLY NEXT
WEEK...BUT LEAVE A TRAILING COLD FRONT NEAR THE CAROLINA COAST.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM EDT...THE EARLY MORNING REGIONAL RADAR LOOP SHOWS A
CLUSTER OF SHOWERS AND THUNDERSTORMS CROSSING THE NORTHERN
MOUNTAINS...A WEAK BAND OF SHOWERS CROSSING THE SOUTHERN
PIEDMONT...AND SPOTTY RETURNS IN BETWEEN. THIS ACTIVITY APPEARS TO
LINE UP WELL WITH THE LEADING EDGE OF A PASSING UPPER VORTICITY LOBE
WHICH WILL PULL NORTHEAST OF THE FORECAST AREA THROUGH 12Z. AFTER A
MID MORNING LULL...COVERAGE IS EXPECTED TO EXPAND ACROSS THE
NORTHERN TIER AGAIN TODAY AS UPPER LEVEL JETLET DIVERGENCE MOVES
OVER THE MOUNTAINS AND COMBINES WITH LOW LEVEL WIND FIELD
CONVERGENCE TO TRIGGER THUNDERSTORMS NEAR THE BLUE RIDGE. THESE
STORMS WILL ADVECT OUT OVER THE FOOTHILLS AND LIKELY STRENGTHEN IN
THE PIEDMONT AS MID LEVEL WINDS INCREASE AND MLCAPE VALUES RISE TO
2000 TO 2500 J/KG ALONG WITH STEEPENING LAPSE RATES. 0 TO 6 KM BULK
SHEAR VALUES COULD REACH 40 KT ACROSS THE I-40 CORRIDOR LATER TODAY.
THIS COMBINATION OF FORCING...INSTABILITY...AND SHEAR WILL FOCUS THE
GREATEST THREAT OF SEVERE THUNDERSTORMS IN THE NW NC PIEDMONT LATE
IN THE DAY. THE SURFACE FRONT DRAPED TO THE NORTH WILL HAVE TO BE
MONITORED CLOSELY FOR ANY SOUTHWARD MOVEMENT THIS AFTERNOON. THIS
BOUNDARY COULD PROVIDE A SOURCE OF STRONGER LOW LEVEL HELICITY NEAR
ANY THUNDERSTORMS...HOWEVER...LARGE HAIL AND DAMAGING WINDS APPEAR
TO BE THE BIGGEST THREATS. EXPECT WARM MAXES SOME 10 DEGREES ABOVE
CLIMO AGAIN.

THE DEEP LAYER WESTERLY FLOW WILL PROMOTE RAPID DOWNSLOPE DRYING
OVERNIGHT. MILD MIN TEMPS WILL REMAIN ABOUT 10 DEGREES ABOVE CLIMO
AS WELL.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 250 AM THURSDAY...AN UPPER RIDGE WILL BUILD BACK OVER THE
SOUTHEAST STATES FRIDAY AND SATURDAY...AS A DEEP TROUGH EJECTS OUT
OF THE ROCKIES INTO THE CENTRAL/SOUTHERN PLAINS. FRIDAY WILL SEE A
BRIEF PERIOD OF DRY NWLY LLVL FLOW...RESULTING IN A DRY DAY WITH
ABOVE NORMAL TEMPS. TEMPS WILL PUSH THE UPPER 80S EAST OF THE
MTNS...ONLY A CATEGORY OR TWO AWAY FROM RECORD HIGHS FOR KGSP AND
KCLT.

FROM FRIDAY NIGHT THRU SATURDAY NIGHT...A LOW PRESSURE SYSTEM WILL
ORGANIZE OVER THE SOUTHERN PLAINS...ACTIVATING A WARM FRONT
EXTENDING FROM KS/MO TO THE CAROLINAS. TO AID IN THE LLVL...THERE
WILL BE A DRY ONSET WEDGE EAST OF THE MTNS...AS SFC HIGH PRESSURE
BUILDS INTO THE GREAT LAKES. THE MODELS AGREE IN GRADUAL MOISTENING
PROFILES AND INCREASING POPS FROM WEST TO EAST...ESP SATURDAY AFTN
THRU SUNDAY MORNING. TEMPS WILL BE NOTICEABLY COOLER ON SATURDAY...AS
CLOUDS INCREASE AND FLOW TURNS OUT OF THE NE. MIN TEMPS WILL REMAIN
WELL ABOVE NORMAL.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 300 AM THURSDAY...MODELS DIVERGE ON THE PATTERN SIGNIFICANTLY
IN THE MEDIUM RANGE. THE GFS IS MORE AMPLIFIED WITH THE FIRST IN A
SERIES OF SHORT WAVE TROFS DIGGING THRU THE GREAT LAKE TO THE EAST
COAST. IT TRACKS A WEAKENING LOW PRESSURE SYSTEM EAST ACRS THE MID
ATLANTIC SUNDAY...THEN BRINGS IN WEAK DRY HIGH PRESSURE BEHIND THE
DEPARTING LOW MONDAY AND TUESDAY. THE LAST TWO RUNS OF THE ECWMF
SHOW A WEAKER FIRST UPPER TROUGH...BUT THEN DIG A DEEPER SECOND
TROUGH FOR TUESDAY AND WEDNESDAY. THE RESULT IS FOR A TRAILING FRONT
TO STALL ATOP THE CWFA...WITH ANOTHER SFC WAVE RIDING NE ALONG THE
BOUNDARY AND PRODUCING MUCH MORE UNSETTLED WX THAN THE GFS. THE
LATEST WPC PREFERENCE SEEMS MORE IN LINE WITH THE ECMWF. BUT FOR NOW
I WILL KEEP POPS MORE IN THE SLGT CHC TO LOW-END CHC RANGE THAN THE
MID TO HIGH-CHC OF THE SUPERBLEND. TEMPS SHOULD RETURN TO NEAR
NORMAL FOR HIGH TEMPS...BUT REMAIN A COUPLE CATEGORIES ABOVE NORMAL
FOR OVERNIGHT LOWS.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...LINGERING EARLY MORNING CONVECTION REMAINS
GENERALLY NORTHWEST OF KAVL...BUT SPOTTY SHOWERS COULD FILL IN
ACROSS THE VICINITY OF ANY TAF SITE AS AN UPPER LEVEL VORTICY LOBE
CROSSES THE REGION THROUGH 12Z. EXPECT MAINLY SCATTERED LOWER VFR
CLOUDS WITH HIGHER AC/CIRRUS CIGS ALOFT FOR THE BULK OF THE DAY.
THUNDERSTORM COVERAGE SHOULD INCREASE THIS AFTERNOON AS UPPER JETLET
SUPPORT ARRIVES...BUT WITH COVERAGE BEST FROM THE NORTHERN BLUE
RIDGE TO PRIMARILY NORTH OF KCLT. MOST SITES WILL GET VCSH WITH A
PROB30 FOR THUNDERSTORMS DURING THE LATE AFTERNOON HOURS...EXCEPT A
BIT EARLIER AT KAVL. DEEP MIXING TODAY SHOULD SUPPORT PLENTY OF
GUSTS INTO THE LOWER 20S. WINDS WILL TOGGLE WESTERLY TOWARD EVENING
AND NW IN THE FRENCH BROAD VALLEY AT KAVL. MOISTURE WILL DIMINISH
RAPIDLY FROM THE WEST TONIGHT IN THE WESTERLY DOWNSLOPE FLOW.

OUTLOOK...ADDITIONAL DRYING IS EXPECTED ON FRIDAY...WITH BRIEF VFR
CONDITIONS...BEFORE UNSETTLED WEATHER AND POSSIBLE RESTRICTIONS
RETURN FROM THE WEST OVER THE WEEKEND.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-06Z
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  93%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  99%     HIGH  97%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.CLIMATE...
RECORDS FOR 04-28

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      86 1986     45 1913     63 1956     29 1928
                1957
   KCLT      90 1943     51 1928     66 1954     36 2005
                                                    2004
                                                    1967
   KGSP      90 1943     54 2013     65 1954     36 1898
                1915
                1914



RECORDS FOR 04-29

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      89 1970     46 1999     63 1956     28 1967
   KCLT      91 1888     48 1999     65 1994     33 1973
                                        1991
                                        1914
   KGSP      91 1917     47 1999     67 1975     32 1992

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...ARK
NEAR TERM...HG
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...HG
CLIMATE...



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