Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 221036

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
636 AM EDT FRI JUL 22 2016

Broad high pressure will remain across the region through early next
week. The high is expected to weaken on Monday, shifting west and
east of the region. Moisture is forecast to gradually increase
across the western Carolinas and northeast Georgia early next week
as a cold front becomes stationary across the mid Atlantic states.


As of 630 AM, updated the forecast to back off the fog mention quite
a bit, as some high level cloud cover along with light mixing in
some areas is resulting in patchy-at-best coverage of reduced visby.
Otherwise, temps have settled to right around normal for this time
of year, but a very quick warm up should commence after sunrise.

Otherwise, a massive upper ridge centered over western Kansas will
continue to compete with a trough along the East Coast for synoptic
supremacy across the forecast area through the period. Progged
thickness values today would support max temps a couple of degrees
higher than on Thursday, somewhat augmented in the foothills and far
western Piedmont by more of a westerly low level flow. Warming temps
aloft and deeper mixing are yielding some rather uninspiring
forecast soundings in terms of the deep convective potential today.
In fact, there`s a rather decent consensus among short term guidance
that dewpoints will mix out so strongly west of a lee trough this
afternoon that forecast sbCAPE falls to less than 500 J/kg at some
foothills sites. This would certainly argue for less coverage of
convection today. Nevertheless, there still appears to be plenty of
buoyancy available across the high terrain, and scattered cells
should generate in the usual spots near the Blue Ridge during
mid-afternoon. Mean cloud-bearing winds and buoyancy gradient would
tend to take any activity almost due south into the western half of
the Upstate and northeast GA Piedmont, so 30 pops will be carried in
those areas. Elsewhere, pops will be slight chance at best. A
well-mixed boundary layer and dry air aloft is resulting in some
healthy dCAPE values in forecast soundings in a weakly sheared
environment. Would therefore expect a handful of microbursts from
pulse storms this afternoon and evening.

Expect diurnal convection to gradually wind down mid-to-late
evening. Will need to keep an eye on the goings on upstream, as the
possibility remains that the remnants of organized convection could
make a run at the CWA, or mid-level vorticies originating from this
activity could initiate new convection in our area. This doesn`t
appear to be all that likely attm, and pops will taper off to less
than slight chance by daybreak Saturday. Min temps will be a
category or so above climo in most areas.


As of 2 AM Friday: On Saturday, h5 ridge will remain across the CWA,
heights around 592DM. NAM forecast soundings indicates the mixing
will deepen to around H8 during the heat of the afternoon. The llvl
thermal and dewpoint profile resembles an inverted V. Using a blend
of MOS guidance, I will indicate sfc dewpoints starting the day
around 70 degrees, then mixing into the upper 60s during the
afternoon. Convective inhibition may linger through the afternoon,
with values ranging as little as 5 to 10 J/kg around 21Z. Convection
appears favored across the mtn ridges and adjacent foothills.
However, weak steering flow and lingering capping may yield at most
isolated coverage. The main headline for Saturday will be the heat.
A blend of model guidance supports highs ranging from the upper 80s
within the mtn valleys to mid 90s across the Piedmont. The high
temperatures combined with afternoon RH around 40 percent should
result in Heat Index values to peak between 100 to 105.

Sunday, models begin to show differences within the mid level ridge.
The 0z GFS shows the ridge centered over the Four Corners with a 587
DM low over northern FL. The 12z ECMWF shows the center of a 594 DM
ridge shifting over the southern Appalachians. The 0z NAM appears to
be the compromise solution and I will favor it through the rest of
the short term. Overall, Sunday appear around one degree hotter than
high temperature and Heat Index values forecast for Saturday. In
addition, capping appears a little weaker for Sunday. I will
continue to favor the mtn ridge for high chc PoPs, spreading schc
PoPs east during the heat of the afternoon.


As of 215 AM Friday: I will favor the ECMWF through the extended
period, Monday through Thursday. Overall the pattern change little
through the period, with gradual lowering of H5 heights as rights
splits and develops a Bermuda ridge and desert SW ridge. Weak cold
fronts are expected to drop and stall across the mid Atlantic
states. This pattern should favor slightly elevated PWs across the
forecast area with slight to moderate instability each afternoon. I
will continue to feature likely PoPs across the ridges and chc PoPs
east Monday through Thursday. Hot conditions will remain across the
region on Monday, very close to Sat and Sun. However, lowering
heights and increase in moisture should favor highs around normal
through the remainder of the period.


At KCLT and elsewhere: Fog has failed to expand beyond very patchy
coverage, and the window of opportunity for anything more widespread
to develop is quickly closing. Will therefore feature a VFR forecast
through the period. That leaves afternoon/evening convection as the
prime concern. Convection is expected to develop across the high
terrain once again this afternoon, and to move almost due south.
PROB30s for TSRA are therefore carried first at KAVL (where VCTS is
also advertised after 18Z), then at the Upstate SC terminals during
the evening. Convection will continue to be omitted from the
forecast at KCLT/KHKY. Otherwise, light S/SW winds will persist
through the period at KCLT, but are expected to turn toward the W/NW
at other terminals to the west of a lee trough.

Outlook: Expect typical midsummer weather with scattered afternoon
and evening showers and thunderstorms through the early next
week. 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...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       Low   38%     High 100%     High 100%     High 100%
KHKY       High  83%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       Low   57%     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:




  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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