Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 232024

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
424 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 420 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. Northward moving outflow
boundaries from the initial convection over the Lakelands is helping
initiate convection along the I-85 corridor. Expect these boundaries
to help initiate convection over the NC SRN Foothills as well.
Convection will remain across the mountains as well. Despite the
moderate instability and dry mid levels, DCAPE values are much
lower, in the 600 to 800 J/kg range, than the previous several days.
Although a severe microburst from the strongest storms cannot be
ruled out, chance is much lower and will be isolated at best. 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 over the Atlantic 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 just about everywhere east of mountains with
some 103/104 along the southeast piedmont fringe. Will keep the HWO
mention for heat going but hold off on any heat advisories at this


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, outflow boundary has moved north across the airfield and
will keep gusty S winds in place until 22z or so. Showers surround
the airfield as well, so expect at least a few rumbles of thunder to
develop until then as well. 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 from the northeast.

Elsewhere, good coverage of convection has developed across the
mountains and I-85 corridor. A series of outflow boundaries have
moved north of the SC sites bringing gusty S to SW winds and
convective development. Have amended to keep the gusts and TSRA in
until 22z. 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...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High  95%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High  95%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  95%     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:



  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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