Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211752

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
152 PM EDT THU JUL 21 2016

Bermuda high pressure and upper level ridging will remain in control
of the weather over the next few days. This will result in well
above normal temperatures...before a weak cold front pushes in from
the north early next week.


As of 125 PM EDT: A broad upper ridge will remain centered over the
southern plains through Friday while a trough axis lingers just off
the Atlantic coast. Weak upper forcing sliding southward over the
southern Appalachians this afternoon is aiding convective
development. Recent HRRR runs produce some robust development over
the southern mountains through mid afternoon. Foothill/piedmont
instability should rise to 2000 to 3000 J/kg of SBCAPE, with
continued 55 dBZ thresholds at 26 kft for severe, except lower from
CLT east in higher DCAPE air. Expect an early peak to the convection
with the passage of the upper jetlet and weak dpva this afternoon,
and then a quick dissipation through the evening hours. Patchy fog
development is possible wherever rain falls and also the lower
mountain river valleys - particularly from the French Broad Valley
and valleys farther southwest.

A little less in the way of upper energy moving southward east of
the ridge into the Carolinas is expected on Friday. Convection will
develop later in the day and primarily over the higher ridges mid
afternoon - with some survival into the adjacent foothills or
perhaps piedmont toward evening. Better insolation, weak downsloping
flow, and less moisture in profiles should lead to higher temps
Friday afternoon than Thursday. More dewpoint mixout is possible as
well, so heat index values should be capped around 100 in the
hottest areas.


At 130 PM Thursday: On Friday night and upper ridge will build east
front the plains across the southern Appalachians, completely
covering our area by late Sunday. Before this ridge overspreads the
area, weak lobes of vorticity may move southeast over the mountains
on the west side of a coastal trough. The models show modest
instability and weak shear each day, supportive of convection, but
not organized storms. Weak steering flow may support locally heavy
rainfall however, especially if cell can train over the same areas.
Temperatures will warm from around 3 degrees above normal to around
6 degrees above normal. Lingering moisture will allow apparent
temperatures to approach 102 degrees in the upper Savannah River
Valley on Friday, and 100 to 105 degrees from the foothills to the
Piedmont on Saturday.


As of 115 PM Thursday...Not much change needed to the going fcst.
Strong ulvl ridging will continue into Mon then slowly break down as
a couple H5 s/w trofs swing across the Glakes region. This will
bring a sfc front into the fcst area late Mon or early Tue. With
little flow aloft this front will become stationary and reinforced
somewhat on Thu as another weak bndry settles in from the north. As
far as the sensible wx goes...sct to num afternoon showers and
thunderstorms will be the norm...esp across the higher
enhanced llvl lift provides broad focusing in a moderately unstable
yet low sheared environment. Max temps were brought down a degree or
two most locale Mon with increasing cloud cover possible...however
heat index values shud still reach adv levels across the srn half of
the CWFA. With weakening in the upper heights and lessening deep
layered subs...max temps will return closer to normal levels Tue
through the period.


At KCLT: The forecast begins will a few cells already on the radar
scope just west of the airfield, but slowly building east while
drifting south. Will include a narrow window of TEMPO TSRA but
mention VCSH otherwise. Will hold onto continued light southerly
flow but with tempo gusts. VFR conditions will then continue
overnight through Friday with light SE to SW surface winds. Profiles
will be a bit drier on Friday and no convection will be mentioned
through 18Z.

Elsewhere: Scattered thunderstorms will threaten the mountain and
foothill airfields through the afternoon hours, with chances best
around KAVL. Will hold onto VCTS at all sites going forward through
at least 22Z. Expect light southerly winds throughout, except
turning NW at KAVL overnight. Fog will be possible overnight at any
location where rain falls late today, but with chances best in the
mountain river valleys. The MOS is hitting KAVL especially hard, but
it has not performed well of late. Will still feature IFR fog after
09Z but not hit dense fog hard yet. Will keep locations dry through
18Z Friday with a later start to convection expected. Surface winds
will become more S to SW but remain less than 10 kt throughout, with
persistent NW flow at KAVL.

Outlook: Expect typical midsummer weather with scattered afternoon
and evening showers and thunderstorms through the weekend. 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 100%     High 100%
KAVL       High 100%     High 100%     High  88%     High  91%
KHKY       High 100%     High 100%     High  84%     High  91%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  89%     High  94%

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      95 1983     69 1974     71 2015     50 1966
                1952        1938        1999
                1934                    1983
   KCLT     101 1987     73 1880     78 1991     56 2007
   KGSP     102 1952     74 1974     79 1934     59 1966


  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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