Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KGSP 210237
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1037 PM EDT WED MAY 20 2015

.SYNOPSIS...
UNSETTLED WEATHER WILL CROSS THE AREA LATE TONIGHT INTO THURSDAY
WITH THE PASSING OF A COLD FRONT. DRIER CANADIAN HIGH PRESSURE WILL
BUILD OVER THE CAROLINAS AND NORTHEAST GEORGIA FRIDAY AND REMAIN
THROUGH THE WEEKEND. SOUTHERLY FLOW MOISTURE AROUND BERMUDA HIGH
PRESSURE WILL GRADUALLY RETURN EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 1030 PM...KGSP RADAR INDICATED ONLY A FEW WEAK RETURNS ACROSS
THE FORECAST AREA. REGIONAL RADAR CONTINUED TO SHOW A BAND OF
SHRA/TSRA ACROSS NRN GA INTO EASTERN TN...SLIDING EAST. THE UPSTREAM
CONVECTION HAS DEVELOPED WITHIN AN AREA OF WEAK INSTABILITY...WHICH
HAS INCREASED SINCE SUNSET. WARMING CLOUD TOPS AND REDUCED LIGHTNING
COUNTS INDICATE THAT THE CONVECTION HAS RECENTLY WEAKEN.
HOWEVER...THE RAP SHOWS LINGERING LOW VALUES OF CAPE REMAINING PAST
MIDNIGHT. I WILL CONTINUE TO FORECAST 20-30 POPS ACROSS THE FORECAST
AREA THROUGH TONIGHT...WITH VALUES RISING DURING THE PRE DAWN HOURS.
THE FORECAST UPDATE WILL ALSO FEATURE ADJUSTMENT TO SKY
GRIDS...TEMPERATURES...AND DEWPOINTS.

AS OF 750 PM...LATEST RADAR TRENDS INDICATED THAT A CLUSTER OF WEAK
SHOWERS WERE MOVING EAST FROM THE GSP AREA...SOUTH OF THE STATE
LINE. THESE SHRA WERE TRIGGER NEAR A WEST TO EAST WARM FROM ACROSS
THE REGION. RECENT SPC ANALYSIS INDICATED THAT THE REGION THE SHRA
EXISTED WAS BECOMING INCREASINGLY LESS UNSTABLE...WITH CIN VALUES
AROUND 50 J/KG AND CAPE AROUND 250 J/KG. IT APPEARS THAT BASED ON
THE STABILITY PATTERN AND HISTORY OF OUTFLOW BOUNDARIES...NEW
CONVECTION WILL LIKELY FAVOR AREAS SOUTH OF THE RECENT ACTIVITY. I
WILL UPDATE THE FORECAST TO REFLECT THE LATEST THINKING.

LATE TONIGHT...A MID LEVEL SHORT WAVE WILL RIPPLE OVER THE SOUTHERN
APPALACHIANS...AS A SFC LOW DEVELOPS ACROSS THE WESTERN CAROLINAS.
CIRCULATION AROUND THE LOW SHOULD RESULT IN A INCREASE IN CAPE
ACROSS THE PIEDMONT. I WILL ADJUST POPS AND TSRA MENTION FOR LATE
TONIGHT INTO THURSDAY MORNING.

AS OF 550 PM...LATEST RADAR IMAGES INDICATED A FEW SHOWERS ACROSS
THE ESCARPMENT...PRIMARILY FROM POLK COUNTY WEST INTO NE GA. THESE
SHOWERS HAVE DEVELOPED IN THE VICINITY OF A WARM FRONT. NORTH OF THE
FRONT...ACROSS THE I-40 CORRIDOR DEWPOINTS RANGED IN THE U30S...WITH
DEWPOINTS IND THE MID TO U60S ACROSS THE UPPER SAVANNAH RIVER
VALLEY. LATEST SPC MESOSCALE ANALYSIS INDICATED CAPES ABOVE 500 J`KG
ACROSS THE UPSTATE...WITH NEAR ZERO ACROSS I-40. I WILL EXPAND CHC
POPS ACROSS THE HIGH TERRAIN ALONG THE CAROLINA BORDER AND NE GA
THROUGH EARLY THIS EVENING. IN ADDITION...I WILL INCREASE CHC POPS
ACROSS THE WESTERN NC MTNS A LITTLE EARLIER...BASED ON RADAR TRENDS
OVER MIDDLE TN. IN ADDITION...OBSERVED TEMPERATURES RANGE A LITTLE
WARMER THAN FORECAST...I HAVE ADJUSTED HRLY TEMPS AND DEWPOINTS.


AS OF 245 PM EDT WEDNESDAY...A WEAK UPPER SHORTWAVE CONTINUES TO
SLIDE THROUGH THE OH/TN VALLEYS AT THIS TIME AMIDST NEARLY ZONAL H5
FLOW.  AT THE SURFACE...A COLD FRONT ASSOCIATED WITH SAID UPPER WAVE
IS SLIDING EAST THROUGH CENTRAL ARKANSAS.  CLOSER TO HOME...REMNANT
COLD FRONTAL PASSAGE FROM TUESDAY HAS BEGUN TO LIFT NORTHWARD AS A
WARM FRONT WITH DEWPOINTS GRADUALLY INCREASING.  RECENT OBS AROUND
THE REGION INDICATE DEWPOINTS IN THE UPPER 40S ALONG AND NORTH OF
I40...WITH DEWPOINTS INCREASING FURTHER SOUTH TOWARD THE I85
CORRIDOR.  IN RESPONSE...THE 18Z MESOANALYSIS INDICATES MINIMALLY
INCREASING CAPE OVER THESE AREAS.  THUS...CONTINUED WITH AN ISOLATED
POP MENTION OVER THE CLIMO FAVORED REGIONS OF THE UPPER FRENCH BROAD
VALLEY...AND ALSO PORTIONS OF THE I85 CORRIDOR.

BEYOND THAT THE FOCUS SHIFTS TO THE ABOVE MENTIONED UPPER WAVE AS IT
APPROACHES FROM THE WEST.  MODELS CONTINUE TO PROG A DYING BAND OF
CONVECTION SLIDING INTO THE NC HIGH TERRAIN OVERNIGHT...BEFORE
PUSHING THROUGH THE REMAINDER OF WESTERN NC THROUGH MID/LATE
MORNING.  EXPECTING CONVECTION TO REINITIATE OVER THE NC PIEDMONT AS
THE PRIMARY UPPER VORT MAX SLIDES BY TO THE NORTH BY AROUND DAYBREAK
THURSDAY...WITH ENOUGH INSTABILITY IN/AROUND THE REGION TO PROMOTE A
FEW THUNDERSTORMS.  ALL IN ALL IT LOOKS RATHER UNEVENTFUL AS THE
FRONT ADVECTS THROUGH THE AREA BY 14Z-15Z WITH SURFACE FLOW VEERING
SHARPLY WEST/NORTHWEST AS HIGH PRESSURE SLIDES IN.  INCREASED
PRESSURE GRADIENT ALONG WITH MIXING OF ENHANCED LOW LEVEL WINDS WILL
LIKELY PROMOTE SOME GUSTS EARLY ON IN THE DAY...AMONGST CLEARING
SKIES.  TEMPERATURES THROUGH THE PERIOD WILL COOL SLIGHTLY BEHIND
THE COLD FRONTAL PASSAGE...HOWEVER SHOULD REMAIN ABOVE NORMAL.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 215 PM WED...THE SHORT RANGE SHAPES UP TO BE FAIRLY QUIET. A
SHORT WAVE WILL PASS BY WELL TO THE N ON THURSDAY EVENING...WHICH
SHOULD PUSH THE UPPER TROF AXIS ACROSS THE WESTERN CAROLINAS/NE
GEORGIA OVERNIGHT. SOME RESIDUAL MOISTURE MAY GET FORCED UP THE W
SIDE OF THE MTNS BY THE NW FLOW...BUT THAT SHOULD NOT AMOUNT TO MUCH
MORE THAN A SMALL CHANCE OF SHOWERS THAT WOULD TAPER OFF BY
MIDNIGHT. FROM THAT POINT ONWARD...THE UPPER PATTERN EVOLVES SLOWLY
WITH A RIDGE AXIS TO THE WEST THROUGH THE END OF SATURDAY. THAT
SHOULD TAKE SURFACE HIGH PRESSURE SLOWLY PAST TO THE NORTH ON FRIDAY
AND SATURDAY...PERHAPS REACHING THE MID ATLANTIC COAST BY SUNSET
SATURDAY. MOISTURE RETURN IS NOT EXPECTED AS THE UPPER RIDGE AXIS
REMAINS WELL TO THE WEST. THUS...EXPECT DRY WEATHER AND NORMAL TEMPS
FOR BOTH FRIDAY AND SATURDAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 205 PM EDT WED...A STRONG ULVL RIDGE WILL CONTINUE TO BUILD
ACROSS THE ERN CONUS SAT NIGHT WITH THE AXIS MOVING OF THE EAST
COAST BY LATE MONDAY. THE GFS H5 Z ENS MEAN AGREES WELL WITH THE OP
MODEL PROGRESSIONS AND VERY LITTLE MEMBER SPREAD IS SEEN ACROSS THE
SE/RN STATES THROUGH MOST OF THE PERIOD. IN THE LOWER LEVELS...A
STRENGTHENING BERMUDA HIGH WILL MAINTAIN A RIDGE ACROSS THE
CAROLINAS SUN/MON BEFORE BREAKING DOWN TUE/WED AS A UPPER S/W AND
COLD FRONT APPROACHES FROM THE WEST.

THERE ISN/T MUCH CHANGE IN THE SENSIBLE WX FCST FROM THE PREVIOUS
PACKAGE. THE BEST GOM MOISTURE FLUX WILL BE MAXIMIZED WEST OF THE
CWFA INTO MON...BEFORE ADDED ATL MOISTURE BEGINS TO ADVECT FROM THE
SE. MODEL SOUNDINGS SHOW A PERSISTENT MLVL SUBS INVERSION INTO MON
AS WELL...SO ANY CONVEC ACTIVITY SHOULD REMAIN RELEGATED ACROSS THE
HIGHER TERRAIN AND SHUNTED WITH DEEPER SHOWERS DEVELOPING MON
AFTERNOON IN LOCALIZED MECH LIFT...POSSIBLY PRODUCING A FEW TSTMS.
POPS REMAIN SLIGHT TO LOW END CHANCE THROUGH MON...WITH AN INCREASE
TO MID RANGE MTN POPS TUE/WED AS THE SUBS PATTERN WEAKENS IN A
DIURNALLY DESTABILIZING ATMOS. TEMPS WEREN/T CHANGED MUCH...STILL
EXPECT A MODEST INCREASE EACH AFTERNOON WITH MAXES ARND 10 DEGREES
ABOVE NORMAL BY WED.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
AT KCLT...LATEST RADAR TRENDS INDICATED THAT A CLUSTER OF WEAK
SHOWERS WERE MOVING EAST FROM THE GSP AREA...SOUTH OF THE STATE
LINE. THESE SHRA WERE TRIGGER NEAR A WEST TO EAST WARM FROM ACROSS
THE REGION. RECENT SPC ANALYSIS INDICATED THAT THE REGION THE SHRA
EXISTED WAS BECOMING INCREASINGLY LESS UNSTABLE...WITH CIN VALUES
AROUND 50 J/KG AND CAPE AROUND 250 J/KG. IT APPEARS THAT BASED ON
THE STABILITY PATTERN AND HISTORY OF OUTFLOW BOUNDARIES...NEW
CONVECTION WILL LIKELY FAVOR AREAS SOUTH OF THE RECENT ACTIVITY. I
WILL KEEP THE EARLY PORTION OF THE CLT TAF DRY AND VFR...WITH LIGHT
SOUTH WINDS. LATE TONIGHT...A MID LEVEL SHORT WAVE WILL RIPPLE OVER
THE SOUTHERN APPALACHIANS...AS A SFC LOW DEVELOPS ACROSS THE WESTERN
CAROLINAS. CIRCULATION AROUND THE LOW SHOULD RESULT IN A INCREASE IN
CAPE ACROSS THE PIEDMONT. I WILL CONTINUE TO INDICATE A PROB30
BETWEEN 9Z-12Z. THE SFC LOW SHOULD TRACK EAST THROUGH THE REST OF
THE DAY...RESULTING IN VEERING WEST TO NORTHWEST WINDS...WITH
MARGINAL GUSTS DURING THE LATE MORNING AND AFTERNOON.

ELSEWHERE...SHOWERS WILL REMAIN IN THE VICINITY OF GSP AND GMU
THROUGH 1Z. VFR WITH LIGHT SOUTH WINDS WILL REMAIN THROUGH TONIGHT.
BY SUNRISE...SFC LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE REGION
AND WILL TRACK EAST THROUGH THE DAY...I WILL INDICATED VCSH AROUND
SUNRISE FOR MOST OF THE TAFS. IN THE WAKE OF THE LOW...CLOUD BASES
WILL RISE AND WINDS SHOULD VEER FROM THE NORTHWEST...WITH GUSTY
CONDITIONS FROM LATE MORNING THROUGH THE AFTERNOON.

OUTLOOK...DEEP HIGH PRESSURE WILL SETTLE OVER THE SOUTHEAST LATE
THIS WEEK AND REMAIN THROUGH TUESDAY. CONDITIONS SHOULD REMAIN
GENERALLY FAIR THROUGH THE PERIOD.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH  88%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH  90%     HIGH  97%     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...SBK
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...SBK
AVIATION...NED



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.