Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 231811

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
211 PM EDT SAT JUL 23 2016

Broad deep layered high pressure will remain across the region
through early next week, with a general weakness developing over the
east coast on Monday. Moisture levels will gradually increase across
the western Carolinas and northeast Georgia by the middle of next
week as a weak cold front settles south into the area.


As of 155 PM EDT, A dominant upper ridge will remain stretched
across the southern tier of the CONUS through Sunday. Under the
eastern periphery of the ridge, a surface lee trough will remain
parked over the foothills/western piedmont. Convective initiation
this afternoon thus far been best in and near the southern mountains
in weak terrain flow and also in the higher dewpoint air over the
southern piedmont where SBCAPE values are 2500+ J/kg. Less coverage
is expected in the NC foothills where dewpoints have mixed very
slightly. Still expect isolated severe potential, mainly
microbursts, with any 55 dBZ cores to 26 kft or so given the very
weak shear profiles. A localized heavy rain threat will continue as
well with steering winds less than 10 kt up the column. The
convection should diminish quickly mid to late evening, but with
isolated shower PoPs overnight in the SW mountains where activity
will end last. Expect mountain valley fog and stratus again with
very mild mins 4 to 8 degrees above climo.

A weak upper low will slide westward under the ridge into northern
FL on Sunday, but with very little attendant moisture affecting the
southeast. Thus expect a similar pattern of mainly diurnal southern
mountain thunderstorm coverage, with more isolated PM activity east
of the mountains across southern and eastern piedmont sections where
dewpoints will be highest. 850 mb temps should be at least another
degree C warmer on Sunday - along with good insolation under the
ridge. This will push heat index values to 100 to 102 everywhere
east of mountains with some 103/104 along the piedmont fringe. Will
keep the HWO mention going but hold off on any heat advisories at
this point.


At 130 PM Saturday: On Sunday night a flat upper ridge will be over
the southern Appalachians. The models vary on the strength and speed
of a coast vort lobe moving inland of the north of a FL surface low
on Sunday night or Monday. The ridge will sift off the coast by
Monday, while heights fall over the OH River Valley. This low
amplitude upper troughing reaches the southern Appalachians by
Thursday, with northern stream vorticity crossing the central
Appalachians late in the day.

At the surface, although better moisture will initially be over the
Gulf States, enough will be present over our area to support
precipitation production. Model time heights show moderate
instability persisting both nights, but shear appears to be rather
weak, limiting the chance of organized convection. Weak
steering flow may support locally heavy rainfall. Temperatures will
run four to six degrees above normal, with daytime apparent
temperatures running around 100 degrees east of the mountains both


As of 1255 PM Saturday...No major changes were made to the going fcst.
The models continue to agree well with the broad upper pattern and
subtrop ridging persisting across the srn states. A sfc front will
stall to the north of llvl ridge Wed and the area will remain in a
warm moist environment. The normally conservative GFS soundings show
decent SBCAPE values easily reached each afternoon in a weakly
sheared atmos. With warm and dry mid levels...this will set the
stage for continued afternoon convec with a handful of pulse severe
microbursts being the main higher end threat. Pop/Sky will continue
with a diurnal trend and above climo values favoring the higher
terrain. Max and min temps will hover around or a bit above normal
through the period.


At KCLT, all eyes will be on developing isolated convection east of
I-77 this afternoon given the northeasterly steering flow. Very
little coverage has developed so far and the latest HRRR is not
bullish for late afternoon around KCLT so only a VCSH will be
maintained. Otherwise, expect mainly scattered VFR cumulus with
bases 050 to 060 this afternoon and again late Sunday morning with
heating and thin debris cirrus from any nearby decaying showers.
Winds will remain mostly light S to SW unless a rogue outflow can
make it to the airfield.

Elsewhere, good coverage of convection has developed from the
eastern escarpment of the mountains to the southern piedmont in weak
convergence and along the axis of 70 to 75 degree dewpoints. This is
occurring mainly south of the TAF sites, with KAVL seeing the best
chance of SHRA/TSRA for the next couple of hours, and then KAND
through early evening. KGSP/KGMU will feature VCTS but will keep
KHKY dry. Otherwise, late day cumulus will dissipate to thin debris
cirrus overnight. Another round of mountain valley fog and stratus
is expected, with associated IFR restrictions at KAVL 09Z to 13Z.
Cumulus will start to build again from mid to late Sunday morning
but with no precip mention through 18Z at the moment.

Outlook: Isolated to scattered afternoon/evening showers and
thunderstorms will continue across the mountains/piedmont through
early next week, with coverage increasing Tuesday into Wednesday.
Morning fog and low stratus will be possible each day in the
mountain valleys and also in locations that receive heavy rainfall
the preceding afternoon/evening.

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  97%     High 100%
KAVL       High 100%     High 100%     High  94%     High  87%
KHKY       High 100%     High 100%     High  97%     High  97%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  97%     High  97%

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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      96 1983     68 1985     71 1934     52 1966
   KCLT     100 1983     73 1938     78 2010     59 1947
                1952                    1883
   KGSP     101 1952     70 1985     79 2010     59 1904


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      92 2010     68 2000     70 2012     51 1895
                2005                    2011
                1987                    2010
   KCLT     101 2010     69 2000     79 2010     62 1947
   KGSP     100 1995     72 2000     77 2010     57 1911




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