Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201839
AFDGSP

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

.SYNOPSIS...
A WEAK RIDGE OF HIGH PRESSURE WILL LINGER ATOP THE REGION THROUGH
TONIGHT. TEMPERATURES WILL WARM ON SUNDAY BEFORE A COLD FRONT
CROSSES THE CAROLINAS LATER THAT NIGHT. COOL AND DRY HIGH PRESSURE
WILL THEN SPREAD ACROSS THE REGION AND REMAIN IN PLACE THROUGH AT
LEAST MID WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 235 PM...DESPITE MDL OUTPUT SHOWING MTN CONVECTION...ATMOS
SHUD REMAIN CAPPED THIS AFTERNOON AND EVENING WITH ONLY RIDGE TOP CU
DEVELOPING. THERE WILL ALSO BE SOME JET STREAM CIRRUS ASSOCIATED
WITH THE LOW PRESSURE SYSTEM MOVING UP THE SERN COAST. GUIDANCE
SUGGESTS A GOOD NITE FOR AT LEAST PATCHY DENSE MTN VALLEY FOG...
WHILE MOST AREAS OUTSIDE OF THE MTNS GENERALLY TOO DRY. SKIES SHOULD
BE MOSTLY CLEAR WITH LOWS NEAR TO SLIGHTLY BELOW NORMAL.

AN UPPER TROF DIGS TOWARD THE AREA SUNDAY PUSHING A FRONT INTO THE
MTNS BY THE END OF THE PERIOD. LITTLE IN THE WAY OF PRECIP IS
EXPECTED UNTIL VERY LATE IN THE PERIOD...THEN ONLY ACROSS THE MTNS
WHERE MOISTURE...FORCING AND INSTABILITY WILL BE BETTER. LOW LEVEL
FLOW REMAINS WLY KEEPING AREAS OUTSIDE OF THE MTNS DRIER WITH A LOW
LEVEL WARM NOSE KEEPING THE ATMOS GENERALLY CAPPED WITH ONLY WEAK
ELEVATED INSTABILITY AT BEST. BRING CHC POP INTO THE TN BORDER
COUNTIES BY LATE AFTERNOON...WITH SLIGHT CHC ACROSS THE REST OF THE
MTNS...AND A DRY FCST ELSEWHERE. CANNOT RULE OUT AN ISOLATED SEVERE
WIND GUST ACROSS THE MTNS GIVEN THE INCREASING SHEAR AND DRY MID
LEVELS...BUT CHC IS LOW. HIGHS WILL BE 5 TO 10 DEGREES ABOVE NORMAL
AS THICKNESSES INCREASE SIGNIFICANTLY AHEAD OF THE FRONT ALONG WITH
THE INCREASING WLY LOW LEVEL FLOW.

&&

.SHORT TERM /SUNDAY NIGHT 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 SATURDAY/...
AS OF 2 PM SATURDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
WEDNESDAY WITH HEIGHTS STEADILY RISING AS A BROAD AND STEEP UPPER
RIDGE SPREADS ACROSS THE REGION. THIS IMPRESSIVE RIDGE IS EXPECTED
TO REMAIN IN PLACE THRU NEW DAY 7 OVER THE EASTERN HALF OF THE CONUS
WHILE ANOTHER STEEP UPPER TROF DIGS DOWN OVER THE WEST COAST BY
THE END OF THE MEDIUM RANGE.

AT THE SFC...STRONG CANADIAN HIGH PRESSURE WILL BE CENTERED TO OUR
NORTH WITH COOL AND DRY AIR OVER THE FCST AREA. OVER THE NEXT COUPLE
OF DAYS...THE LONG RANGE GUIDANCE SUGGESTS THAT THIS HIGH WILL
GRADUALLY DRIFT EASTWARD WITH SOME DEEPER LYR MOISTURE ENCROACHING
UPON THE CWFA FROM THE SOUTH AND EAST. THE MODELS DIFFER WITH
REGARDS TO HOW FAR NW THIS DEEPER MOISTURE WILL EXPAND. THE ECMWF
CONTINUES TO SHOW GREATER COVERAGE OVER THE CWFA ON FRI AND MOST OF
SAT WHILE THE NEWER RUN OF THE GFS KEEPS THE MOISTURE PLUME MORE TO
THE SOUTH ON FRI AND THEN EXPANDS IT FARTHER NORTH ON SAT.
INTERESTINGLY...THE LATEST 12Z RUN OF THE CMC MODEL KEEPS THE DEEPER
MOISTURE EVEN FARTHER SOUTH THAN THE GFS THRU ITS FCST ENDING TIME
OF 12Z FRI. BASED ON THE MIXED MODEL SPREAD TOWARDS THE END OF THE
FCST PERIOD...I DID NOT MAKE ANY MAJOR CHANGES TO THE SENSIBLE FCST.
I GRADUALLY INCREASED POPS TO SLIGHT CHANCE DURING THE LATTER PART
OF THURS AND KEEP THEM THERE FOR FRI. I DID INCLUDE AN AREA OF SOLID
CHANCE VALUES OVER THE FAR SOUTHERN ZONES FOR SAT AFTERNOON INTO SAT
EVENING...OTHERWISE MOST OTHER AREAS STILL ONLY CARRY SLIGHT CHANCE.
TEMPS WERE CHANGED LITTLE WITH VALUES REMAINING A FEW DEGREES BELOW
CLIMATOLOGY FOR LATE SEPT.

&&

.AVIATION /19Z 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...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     MED   71%     HIGH  87%
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...JPT
NEAR TERM...RWH
SHORT TERM...CDG
LONG TERM...JPT
AVIATION...RWH





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