Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201749
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
149 PM EDT SAT SEP 20 2014

.SYNOPSIS...
A WEAK RIDGE OF HIGH PRESSURE WILL LINGER ATOP THE REGION THROUGH
TONIGHT. TEMPERATURES WILL MODERATE OVER THE WEEKEND BEFORE A COLD
FRONT CROSSES THE CAROLINAS SUNDAY NIGHT. COOL AND DRY HIGH PRESSURE
WILL SPREAD ACROSS THE REGION THROUGH MID WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 145 PM...RIDGE TOP CU DEVELOPING AS CIRRUS MOVES IN FROM THE
SOUTH ASSOCIATED WITH THE COASTAL LOW. TEMPS ARE RUNNING A LITTLE
HIGHER THAN EXPECTED...SO BUMPED UP HIGHS SLIGHTLY. OTHERWISE...
GOING FCST ON TRACK SO ONLY MINOR CHANGES FOR CURRENT CONDITIONS.

AS OF 1035 AM...SKIES ARE MOSTLY CLEAR THIS MORNING AS DRIER AIR
WORKED IN EARLIER THAN EXPECTED. THAT SAID...THERE IS LINGERING LOW
LEVEL MOISTURE THAT WILL PRODUCE CONVECTIVE CU WITH HEATING...
ESPECIALLY ACROSS THE MTNS. LATEST CONVECTIVE ALLOWING GUIDANCE
SUGGESTS ANY CONVECTION THAT DEVELOPS WILL BE ACROSS THE SWRN MTNS.
THE 12Z NAM AGREES. HOWEVER...KEPT THE FCST DRY GIVEN THE CAPPED
ATMOS. OTHERWISE...GOING FCST IS GENERALLY ON TRACK...SO ONLY MINOR
CHANGES NEEDED.

1030 UTC UPDATE...SKY COVER HAS BEEN UPDATED FROM THE LATEST
INFRARED SATELLITE IMAGERY. POPS HAVE BEEN FURTHER REDUCED ALONG THE
BLUE RIDGE PER RADAR TRENDS.

AT 230 AM EDT SATURDAY...AN UPPER TROUGH WILL AMPLIFY OVER THE UPPER
MS RIVER VALLEY TODAY...WHILE AN UPPER LOW PERSISTS OFF THE GA
COAST. THE UPPER TROUGH REACHES THE LOWER GREAT LAKES TONIGHT...
WHILE THE UPPER LOW WEAKENS AND MOVES UP THE CAROLINA COAST.

A RIDGE OF HIGH PRESSURE ASSOCIATED WITH A HIGH OFF THE COAST OF
NOVA SCOTIA WILL REMAIN BANKED UP AGAINST THE SOUTHERN APPALACHIANS.
THE MODELS SHOW DRIER AIR MOVING INTO OUR AREA FROM THE NE TODAY...
LIMITING THE CHANCE OF PRECIPIATION....DESPITE A LIGHT UPSLOPE FLOW
FROM THE SE. BY TONIGHT SURFACE WINDS BACK FROM NE TO N...
INTRODUCING A DOWNSLOPE COMPONENT...AS A SURFACE WAVE MOVES UP THE
CAROLINA COAST. TEMPERATURES WILL RUN NEAR NORMAL.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
AS OF 145 PM EDT SATURDAY...THE SHORT TERM FORECAST PERIOD
INITIALIZES SUNDAY EVENING AMIDST AN UPPER TROF EJECTING TO THE EAST
ACROSS THE GREAT LAKES REGION WITH A WEAK SURFACE LOW SLIDING
THROUGH SOUTHERN ONTARIO.  A COLD FRONT WILL BE DRAPED FROM THIS
PARENT SURFACE LOW SOUTHWEST ALONG THE APPALACHIAN MOUNTAINS.
CLOSER TO HOME...A WEAK UPPER/SURFACE LOW OFF THE CAROLINA COASTLINE
WILL MIGRATE NORTHWARD WITH NO SIGNIFICANT IMPACTS EXPECTED.  THERE
REMAINS SOME UNCERTAINTY REGARDING THE AMOUNT OF ONGOING CONVECTION
AT FORECAST INITIALIZATION.  THE USUALLY MORE AGGRESSIVE/UNSTABLE
NAM INDICATES NEARLY 1000J/KG SBCAPE ACROSS THE WARM SECTOR WITH
CONVECTION SPREAD OUT ACROSS THE HIGH TERRAIN AND NC
PIEDMONT...LIKELY TIED TO THE PREFRONTAL SURFACE TROF AS A FOCUSING
MECHANISM.  THE GFS/ECMWF FAVOR A MORE STABLE SOLUTION WITH LITTLE
TO NO PREFRONTAL TROF FOCUSED ACTIVITY.  ALTHOUGH SHEAR WILL BE
INCREASING...THE BEST UPPER JET DYNAMICS WILL PASS BY TO THE
NORTH...THEREFORE DECIDED TO LEAN TOWARD THE MORE SUBTLE SOLUTIONS
OF THE GFS/ECMWF.  THE FRONT WILL SWEEP THROUGH THE REGION DURING
THE OVERNIGHT HOURS WITH OVERALL CONVECTIVE COVERAGE EXPECTED TO
DISSIPATE WITH LOSS OF HEATING.  THE FRONT LOOKS TO CLEAR THE
FORECAST AREA BY NLT NOON ON MONDAY BEFORE ANY DIURNAL HEATING
INDUCED INSTABILITY CAN PLAY A FACTOR.

BEHIND THE FRONT ON MONDAY AFTERNOON...UPPER TROF AXIS AND
ASSOCIATED VORTICITY MAXIMA WILL SLIDE THROUGH THE SOUTHERN/CENTRAL
APPS.  MODERATE TO STRONG NORTHWEST FLOW THROUGH THE PROFILE WILL
LEAD TO THE POSSIBILITY OF A FEW UPSLOPE INDUCED SHOWERS ALONG THE
SPINE OF THE APPS.  THUS THE FORECAST WILL FEATURE CHANCE LEVEL POPS
ACROSS THE HIGH TERRAIN SUNDAY NIGHT TAPERING TO SLIGHT CHANCE POPS
ACROSS THE REMAINDER OF THE FORECAST AREA THROUGH MONDAY MORNING TO
ACCOUNT FOR PASSAGE OF THE FRONT AND WEAK NORTHWEST UPSLOPE FLOW
SHOWERS ALONG THE TN LINE.  THE ABOVE MENTIONED UPPER FEATURES WILL
SLIDE EAST LATE IN THE DAY MAKING WAY FOR RISING HEIGHTS AND
CANADIAN HIGH PRESSURE AT THE SURFACE THAT WILL LAST THROUGH THE
PERIOD.  THIS WILL YIELD MORE FALL LIKE CONDITIONS WITH TEMPERATURES
GENERALLY 8-10 DEGREES BELOW NORMAL AMONGST DRIER NORTHERLY FLOW.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
AS OF 220 AM SATURDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z
TUESDAY WITH THE LONGWAVE UPPER TROF ALREADY LIFTED NE OF THE REGION
ON THE GFS AND THE LAST FRAME OF THE NAM SHOWING AXIS OF THE TROUGH
ALIGNED ACROSS THE EAST COAST STATES.  HEIGHTS WILL BE RISING FROM
THE WEST. THE CENTER OF THE HIGH WILL MOVE FROM INDIANA 12Z TUES TO
NEW ENGLAND 12Z WED. THIS HIGH WILL REMAIN NEAR NEW ENGLAND CREATING
A COOL WEDGE DOWN THE EASTERN SEABOARD FOR OUR REGION WED THROUGH
FRI. ANOTHER HIGH WILL CROSS CENTRAL CANADA IN MID WEEK AND MERGE
WITH THIS FIRST HIGH. 925MB WIND WILL BE FROM THE NE TUES AND BECOME
MORE EASTERLY WED AND THURS WITH A GOOD FETCH OFF THE ATLANTIC.
CLOUDINESS WILL SLOWLY INCREASE. THE UPPER PATTERN IN MID WEEK WILL
BE A BROAD RIDGE ACROSS THE CONTINENTAL 48 STATES. A TROUGH ENTERS
THE WESTERN STATES AT THE END OF THE WEEK. IN THE LATER HALF OF THE
WEEK THERE WILL BE DEEPER MOISTURE TO THE SOUTH OF OUR REGION AND
THE SEMI UPSLOPE WITH A GENERAL EAST WIND AT TIMES DEPENDING ON THE
ORIENTATION OF THE HIGH. WILL CONTINUE TO SLIGHT POPS FOR THE SOUTH
AND EAST ZONES LATE IN THE WEEK. TEMPS WILL BE A FEW DEGREES BELOW
NORMAL WITH PERHAPS THE COOLER OF THESE DAYS BEING ON THURSDAY.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ALL BUT KAVL...VFR. FEW CONVECTIVE CU WITH JET STREAM
CIRRUS THIS AFTERNOON. CU DIMINISHES THIS EVENING BUT CIRRUS
REMAINS. CONVECTIVE CU RETURNS WITH HEATING SUNDAY. NELY WIND
BECOMES LIGHT NLY OVERNIGHT THEN INCREASES FROM THE WNW WITH MIXING
SUNDAY.

KAVL...RIDGE TOP CU THIS AFTERNOON DISSIPATES THIS EVENING LEAVING
SOME CIRRUS IN PLACE. ALL PARAMETERS SHOW A GOOD NIGHT FOR VALLEY
FOG. HAVE GONE LIFR AROUND DAYBREAK TO INDICATE THIS...BUT VLIFR
QUITE POSSIBLE. FOG SHUD BURN OFF QUICKLY AFTER DAYBREAK WITH CU
DEVELOPING AGAIN WITH HEATING. SLY WIND THIS AFTERNOON BECOMES CALM
OVERNIGHT THEN PICKS UP FROM THE NORTH WITH MIXING SUNDAY.

OUTLOOK..A COLD FRONT WILL BRING A CHANCE FOR RESTRICTIONS MAINLY
OVER THE MTNS SUNDAY NIGHT AND MONDAY MORNING. HIGH PRESSURE BUILDS
BACK IN EARLY NEXT WEEK.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-17Z
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 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...DEO
NEAR TERM...JAT/RWH
SHORT TERM...CDG
LONG TERM...DEO
AVIATION...RWH






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