National Weather Service Weather Forecast Office

Area Forecast Discussion

217
FXUS62 KGSP 182042
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
442 PM EDT TUE JUN 18 2013

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL CONTINUE TO MOVE EAST ACROSS THE AREA
THROUGH THIS EVENING...DRIVING SCATTERED SHOWERS AND THUNDERSTORMS.
ANOTHER UPPER LEVEL DISTURBANCE WILL CROSS THE REGION ON
WEDNESDAY...BUT WITH SOME DRYING OF THE ATMOSPHERE. HIGH PRESSURE
WILL BUILD OVER THE AREA FOR THE WEEKEND...MAINTAINING A WARM AND
MOIST AIRMASS WITH A CHANCE OF SHOWERS AND THUNDERSTORMS EACH
AFTERNOON.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
400 PM UPDATE...CATEGORICAL POPS SEEM APPROPRIATE FOR THE
MTNS/FOOTHILLS OVER THE NEXT HOUR OR SO...BUT LOWERED THEM A TAD TO
ACCOUNT FOR SOME GAPS IN COVERAGE. ACTIVITY WILL MOVE INTO THE
CLEARER AND MORE UNSTABLE PIEDMONT BEFORE INSTABILITY STARTS TO DROP
OFF WITH THE SETTING SUN...SO EXPANDED LOW CAT POPS INTO THE
PIEDMONT BRIEFLY AS POPS DIMINISH IN THE WEST. ADJUSTED TEMPS
SLIGHTLY GOING INTO EVENING BASED ON 4 PM OBS. TRIED TO ACCOUNT FOR
CLOUD COVER HOLDING TEMPS NEARLY STEADY IN SOME PLACES...AS WELL AS
OUTFLOW POTENTIALLY COOLING THINGS OFF IN THE WARMER AREAS IN THE
LOWER FOOTHILLS AND PIEDMONT.

AS OF 230 PM EDT TUESDAY...A BIT OF A TRICKY FCST THIS AFTERNOON AND
EARLY EVENING. THE OVERALL PATTERN IS WELL AGREED UPON BY THE
MODELS...HOWEVER CONFIDENCE IN THE EVOLUTION OF S/W ENERGY ACROSS
THE CWFA IS NOT VERY HIGH DUE TO MODEL DIFFERENCES. THE LATEST RADAR
SHOWS AN UNSTABLE AIRMASS TO THE WEST BECOMING INCREASINGLY UNSTABLE
INTO THE WRN ZONES. VSBY SAY SHOW GOOD CLEARING AND HEATING TAKING
PLACE...BUT IN A DEEPLY MOIST ATMOS SBCAPE VALUES WILL LIKELY REACH
ONLY MOD LEVELS. THIS IS A LITTLE EVIDENT IN THE LOW TOP CONV SEEN
TO THE WEST. IN ANY REGARD...WILL ANTICIPATE TSTMS DEVELOPING AHEAD
OF THE WEAK COLD FRONT AND DEPENDING ON THE STRENGTH OF THE CROSS
S/W ENERGY...SOME OF THESE COULD BECOME STRONG TO SEVERE THIS
AFTERNOON. THE MAIN THREAT WOULD BE LARGE HAIL AND PERHAPS DAMAGING
WINDS AS DRIER AIR WORKS INTO THE MLVLS. EXPECT A WIND SHIFT ACROSS
THE MTNS AROUND 00Z AND INTO THE UPSTATE NEAR 05Z. THIS WILL
SUPPRESS ANY ACTIVITY TO THE SOUTH WITH A LOWER THETA/E AIRMASS
MIXING IN. SOME PATCHY DENSE FG IS POSSIBLE AROUND DAYBREAK IN THE
MTN VALLEYS AS THE PGRAD IS NOT REAL TIGHT BEHIND THE FRONT AND
BROADENS THROUGH 12Z.

A CP HIGH WILL WORK SOUTH INTO THE OH VALLEY TOMORROW AND PUSH A
BACKDOOR COLD FRONT INTO THE NRN ZONES BY THE AFTERNOON. THERE IS
NOT MUCH MOISTURE AVAILABLE WITH THIS SYSTEM SO WILL EXPECT THE BEST
PRECIP CHANCES ACROSS THE MTNS...WHERE AN E/LY UPSLOPE FLOW BRINGS
IN ATL MOISTURE. POPS HAVE BEEN HELD TO SLIGHT/CHANCE ACROSS THE
MTNS AND SLIGHT ELSEWHERE...WITH MAINLY -SHRA AND PERHAPS A MODERATE
THUNDERSTORM OR TWO ACROSS THE FHILLS AND MTNS. MAX TEMPS SHOULD
STILL BE A COUPLE DEGREES BELOW NORMAL WITH THE NE/LY SFC FLOW AND
AIRMASS MIXING.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 200 PM EDT TUESDAY...THE SHORT TERM WILL BE DOMINATED BY
SURFACE HIGH PRESSURE THAT WILL SET UP CAMP OFF THE NEW ENGLAND
COAST WHICH WILL REMAIN RIDGED SWD INTO THE SOUTHERN APPALACHIANS
THROUGH FRI. THE UPPER AIR PATTERN WILL BE ALMOST INDETERMINATE IN
THE DEEP SOUTH WITH VERY WEAK FLOW. THE AREA WILL BE BETWEEN A
TROUGH WELL TO THE NE AND AN UPPER RIDGE OVER THE SOUTHERN PLAINS.
HENCE...NO SIGNIFCANT UPPER FORCING IS ANTICIPATED. MODEL TIME
HEIGHTS INDICATE THAT MOISTURE WILL REMAIN RELATIVELY HIGH IN THE
BOUNDARY LAYER WITH DRYING ESSENTAILLY ABOVE 10KFT THROUGH THU NIGHT.
HOWEVER...MOISTURE IN THE COLUMN IS FORECAST TO DECREASE ON FRI.
HENCE...THE WEATHER SHOULD BE DRIVEN BY MAINLY BY THE LOW LEVEL WIND
FLOW AND ANY MECHANICAL LIFT IT MUSTERS...PLUS DIURNAL HEATING.
THEREFORE...MAINLY DIURNAL/SCATTERED CONVECTION IS EXPECTED PRIMARILY
OVER THE MOUNTAINS...WITH PERHAPS A DOWN TICK IN COVERAGE ON FRI
AFTERNOON DUE TO THE DRYER AIR. WITH THE WEAK UPSLOPE FLOW...SOME
NOCTURNAL WIDELY SCATTERED SHOWERS WILL REMAIN POSSIBLE OVER THE
MOUNTAINS WED/THU NIGHTS. USED AN ALLBLEND APPROACH TO TEMPERATURES
WHICH PRODUCED MAX TEMPS ON THU AND FRI ABOUT A CATEGORY BELOW
AVERAGE.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 2 PM TUESDAY...THE MAIN FEATURE FOR THE EXTENDED PERIOD IS A
RIDGE OF HIGH PRESSURE THAT WILL SET UP OVER THE SOUTHEASTERN CONUS
OVER THE WEEKEND AND INTO MONDAY. THE BERMUDA HIGH WILL REMAIN
SITUATED OVER THE ATLANTIC OFF THE EAST COAST...SETTING UP A MOIST
SOUTHEASTERLY TO SOUTHWESTERLY LOW-LEVEL FLOW REGIME FOR THE REGION.
THIS WILL DRIVE MAINLY DIURNAL CONVECTION FOR THE PERIOD...WITH
GREATER CHANCE POPS FAVORING THE HIGHER ELEVATIONS EACH AFTERNOON
THROUGH THE MIDDLE OF NEXT WEEK. THE PERSISTENT RIDGE WILL ALLOW FOR
A SLIGHT WARMING TREND...WITH TEMPS NEAR TO SLIGHTLY ABOVE AVERAGE
BY THE END OF THE EXTENDED PERIOD.

&&

.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
AT KCLT...THE UPPER S/W ENERGY IS BEGINNING TO INTERACT WITH
INCREASING INSTABILITY TO THE WEST OF THE TERMINAL AND THIS SHOULD
PRODUCE SOME DEEPER CELLS AND TSTMS ACROSS THE AREA THRU SUNSET.
GIVEN ABUNDANT MOISTURE ENABLING ESPECIALLY HIGH RAINFALL
RATES...BRIEF IFR VSBY IS LIKELY TO OCCUR DURING TS IF THEY PASS
OVER THE FIELD. MOST ACTIVITY TO THE N OF THE FIELD ATTM SO GUSTS OF
OUTFLOW FROM THE N POSSIBLE TOO. EXPECT MAINLY -SHRA IN THE VICINITY
AFT 01Z. WITH THE PRECIP TODAY AND POSSIBLY THIS EVENING...WILL
INCLUDE MVFR FG FOR A FEW HRS NEAR DAYBREAK EVEN WITH A MIX OF A
LOWER T/TD AIRMASS.

ELSEWHERE...STARTING TO SEE THE CONV ACTIVITY TO THE WEST INCREASE
IN COVERAGE AND INTENSITY..WHILE A ULVL WAVE WILL PUSH ALL THIS
EAST THROUGH THE OVERNIGHT. EXPECT PERIODIC THUNDER AT ALL SITES
BEGINNING AFT 18Z OR SO AND CONTINUING THROUGH THE EARLY
EVENING...PRODUCING ISOLATED IFR VSBYS IN HVY RA. WILL COVER
REMAINING LOW END ACTIVITY BEFORE THE COLD FRONT CROSSES WITH
VCSH/S. ALL SITES SHOULD SEE RESTRICTIVE VSBY OR CIGS IN THE MVFR
RANGE AROUND DAYBREAK...WITH KAVL LIKELY EXPERIENCING IFR CONDS.

OUTLOOK...A MODERATELY UNSTABLE ATMOSPHERE COMBINED WITH EASTERLY
FLOW MAY LEAD TO SHOWER AND THUNDERSTORM DEVELOPMENT
MIDWEEK...CAUSING SPOTTY RESTRICTIONS.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-20Z
KCLT       HIGH 100%     HIGH 100%     LOW   53%     HIGH 100%
KGSP       HIGH 100%     HIGH  95%     MED   68%     HIGH  85%
KAVL       HIGH  93%     HIGH  96%     HIGH  80%     HIGH  85%
KHKY       HIGH 100%     HIGH 100%     MED   67%     HIGH  85%
KGMU       HIGH 100%     HIGH  88%     LOW   45%     HIGH  85%
KAND       HIGH 100%     HIGH  98%     MED   66%     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...VISIN
NEAR TERM...SBK/WIMBERLEY
SHORT TERM...LG
LONG TERM...VISIN
AVIATION...SBK/WIMBERLEY