Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 251802 AAC

Area Forecast Discussion...UPDATED
National Weather Service Greenville-Spartanburg SC
202 PM EDT MON JUL 25 2016

Broad high pressure will linger over the Southeast through the
remainder of the week, supporting plenty of heat and humidity. A
front is expected to remain more or less stationary from the mid
Atlantic through the Ohio Valley.


As of 145 PM...Convective temps have been reached per visible and
radar trends. However, showers have struggled to become deep enough
for thunder so far. It seems the upper ridge is in a position to
keep things somewhat suppressed. The latest SPC mesoanalysis shows
SBCAPE around 2000 J/kg, with some higher amounts along a lee trough
in western NC. This instability may be enough for at least a few
TSTMS to develop. And with DCAPE between 1000-1400 J/kg, any storms
that can get an icy core may produce wet microbursts. Another
concern this afternoon is heat indices, which are running a little
higher than this time yesterday. Dew points are remaining in the
lower 70s across much of the Piedmont, as temps reach the mid 90s.
So far heat indices are generally between 96-104 across the Piedmont.

Tonight...convection should wane with loss of heating this evening,
leaving some debris cloudiness around. Patchy fog will likely
develop again in the mountain valleys. Lows will remain a couple
categories above normal (upper 60s mountains to mid 70s piedmont).

Tuesday...little change in the overall set up and air mass from
Monday. Model guidance has slightly higher PoPs, perhaps due to a
frontal boundary approaching from the north. In fact, most of the
guidance keeps dew points more elevated across the area, with
widespread lower to mid 70s even during peak heating. This should
result in a little more CAPE. Temps are forecast to be a degree or
two cooler, but with the increased humidity, heat indices will again
range in the upper 90s to 104.


As of 310 AM Monday, the subtropical ridge will remain the dominant
synoptic scale feature across the Southeast during the short term.
Surface reflection/Bermuda high will support plenty of heat and
humidity across our area for the foreseeable future. A lee trough and
the usual terrain effects will provide the primary source of lift
for initiating deep convection Tue afternoon. Buoyancy profiles are
quite impressive across the mountains during this time, and 50-60
pops appear warranted. There are some hints that surface dewpoints
could mix out outside the mtns in response to westerly flow, but at
least scattered activity should push off the high terrain by as
dewpoints begin to recover by evening.

Instability profiles continues to improve over a larger area on Wed,
while a surface boundary associated with Midwest height falls will
approach the area from the NW. Thus, while more convection is likely
to initiate across the forecast area Wed afternoon, there will also
be an increasing chance for frontal activity to push into the
mountains during the late afternoon/evening. Another round of 50-60
pops will be forecast for the mtns, with 30-40 percent chances
across much of the foothills and Piedmont. Wind shear profiles will
remain weak through the period, thus chances for organized
convection will be small. However, increasing coverage of
convection, along with healthy downdraft CAPE forecasts will likely
result in increasing chances for microbursts into mid-week. Temps
will remain a good 5 degrees above climo through the period.


As of 210 PM Sunday...Little to no change in the pattern or sensible
weather is anticipated late week into the weekend, as Bermuda high
pressure continues to support at least seasonal levels of heat/
humidity/instability, while weak synoptic scale boundary is expected
to remain draped in the vicinity of the Ohio Valley. The only
potential break in the monotony would be a weak disturbance that
global model guidance is trying to develop within a weakness in the
subtropical ridge across the northwest Gulf of Mexico later this
week. Moisture associated with this feature could get advected north
toward the end of the week, as a weak mid-level wave moves out of
the Plains. However, even the more aggressive guidance keeps the
deeper moisture west of our forecast area through Day 7. Overall,
near to slightly above climo pops and near to slightly above climo
temps look to be the most likely scenario for Days 4-7.


At KCLT and elsewhere...Convection beginning to become a little
deeper around the mountains and along a piedmont trough, but still
limited to SHRA at time of 18z TAF issuance. Expect a few of these
cells to become TSRA, but mainly in the mountains. Only KAVL will
mention TS, but will keep VCSH at KAND as it is surrounded by small
SHRA. Confidence is too low elsewhere, but timely amendments will be
made, if any TS manage to develop near the other sites. Otherwise,
expect VFR conditions with cumulus bases around 6000 ft and a light
SW wind, becoming somewhat VRB tonight. The one exception being
possible fog and/or stratus at KAVL late tonight due to valley fog
potential. Tuesday looks similar to today, with isolated convection
in the Piedmont and scattered to numerous in the mountains.

Outlook: Isolated/scattered afternoon/evening showers and
thunderstorms will continue across the mountains/piedmont through
much of the week, with coverage increasing a bit each day. Morning
fog and low stratus will continue in the mountain valleys around
daybreak each day, and also be possible 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%     Med   72%     High  91%
KHKY       High 100%     High  99%     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      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


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      94 1949     72 1911     71 2012     49 1911
                1940                    2010
   KCLT     100 2005     74 1920     76 1992     60 1904
                1940                    1940
                1914                    1936
   KGSP      99 2010     76 1920     76 2005     53 1911
                1995                    1940




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