Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 260247

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1047 PM EDT MON JUL 25 2016

Broad surface high pressure will linger in the southeastern CONUS
before sliding offshore as a surface low develops and moves
northeast across the Midwest and Great Lakes regions. A surface
front/boundary will remain off to our north and linger within a
region between the Ohio Valley, lower Great Lakes, and Mid-Atlantic


As of 1045 PM EDT Monday:  Latest spc mesoanalysis indicates the
effects of heating loss as well as convective overturning across
the western Upstate and portions of northeast GA where shra/tsra has
been most prevalent over the last two hours.  With that, sbcape have
now fallen into the 500-1000j/kg range with weak cin consuming the
region.  That said, enough elevated instability remains in place to
allow for persistence of current I85 corridor convection, at least
for another hour or so.  Thus, opted to slow the trend of lowering
pops thereby allowing chances to remain in place through midnight
before all pops fall off into the overnight.  Guidance continues to
favor patchy fog across the region by daybreak, especially for areas
that experienced abundant precipitation this afternoon/evening.
The most dense of which will likely occur in the usual locales
of the mtn valleys, with the Little TN and French Broad valleys
seeing the greatest impacts.  As for the remainder of the area,
think visbs will remain above DFA criteria on the whole, however
wouldn`t be suprised to see some patchy dense fog about the region.

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 230 PM EDT Monday: Subtropical ridge will remain in place
across the Southeast through the short term, with Bermuda high off
the Atlantic Coast keeping the warm and moist airmass in place
across the region (typical summertime conditions). As has been the
case the past few days, lee troughing will remain in place along the
eastern slopes of the Appalachians. A stronger upper high over the
Desert Southwest will retrograde slightly westward through the
period as a weakness moves onshore over the Lower Mississippi Valley
and connects with a low-amplitude wave traversing the northern tier
of the country, which will drag a weak front into the Ohio Valley at
the start of the period. The ridge will remain strong enough to keep
the front stalled to our northwest, but a reinforcing shortwave
coming out of the Rockies into the Plains late in the period will
make some headway in actually moving the front towards our area, to
impact us in the extended.

As for sensible weather impacts, the heat and humidity will remain,
though heat indices will continue to hover a few degrees below
advisory criteria levels. Typical summertime afternoon showers and
thunderstorms will continue, though the pattern will be slightly
enhanced on Thursday over the mountains as the front slowly sags
closer to the area and enough of a shortwave pushes through aloft to
enhance the lee troughing (the GFS actually closes off a low over
the NC Piedmont). Because of the approach of the front and
shortwave, some deep-layer shear actually pushes into northwest
zones Thursday afternoon (right around 30kt 0-6km along with sbCAPE
values on the GFS between 2000-3000 J/kg, pretty impressive given
the GFS is usually a little less robust on CAPE values), so with the
enhanced convective potential we could also see a slight uptick in
the potential strength of storms, with maybe more than just
"isolated" severe thunderstorms possible. For now, we remain in
General Thunder for the Day3 outlook but would not be surprised to
see that go to Marginal in later updates.


As of 210 PM Monday... The general consensus is that typical weather
for July will dominate the sensible weather pattern throughout this
coming weekend. Have gone with mainly to perhaps slightly above
climo POPs and temps for the period, with moderate heat and
instability remaining in place across the CWA. A surface-based
boundary/front will remain off to our north and draped across an
area between the Ohio Valley and lower Great Lakes regions. Closer
to home, a Bermuda High centered off the Atlantic coast will
continue to support the aforementioned heat and instability. A 500
mb trough axis will also be in place across the Midwest. This trough
then begins to breakdown and eject northeastward by the end of the
period. Diurnal POPs should generally favor the mountain zones as
westerly to southwesterly flow dominates with the greatest moisture
axis remaining just to the west of the CWA along and just ahead of
the previously mentioned trough. This may lead to some weak
downslope flow that may briefly suppress convective activity in the
foothills and piedmont areas during the early afternoon hours. Upper
ridging then builds across the Great Lakes region by the beginning
of next week.


At KCLT:  VFR through the period.  High pressure to prevail over
the next 24 hours leading to rather quiet and restriction free
conditions.  With that, light/moderate sw flow will calm tonight
before increasing yet again around mid/late morning Tuesday as
weak mixing commences.  At that point am expecting winds out of
the sw in the 6-10kts range with an occasional gust possible.
Skies this evening will sct out leading to only mid/high clouds
ahead of developing cu late on Tuesday morning.  As for convection,
think poor mid lvl lapse rates will once again be the primary
hindrance over the NC piedmont on Tuesday therefore kept all wx
from taf at this point aside for a token vcsh during the afternoon.
Confidence is low, even in any developing convection reaching
limits conducive of lightning.

Elsewhere:  Similar to that of KCLT above, however with visb/cig
restrictions favored at KAVL where ifr is included, east across
the fthills at KHKY where mvfr is included.  Considering the
persistence of the pattern, and shra/tsra in the vicinity
this afternoon, confidence is marginally high in occurrence.
Otherwise, no restrictions featured at any SC site aside for at
KAND where afternoon convection could promote light mvfr fog to
occur around daybreak.  Aside from the above mentioned cigs in
the mtns, expecting skies to sct through the evening leading to
mid/high cirrus before llv cu redevelops late Tuesday morning.
Did favor convection by way of prob30s at all sites on Tuesday,
generally with about the same coverage as occurred on Monday over
the low terrain, perhaps a bit better in the mtns.

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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  95%     Low   47%     High  88%     High 100%
KHKY       High 100%     High  95%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     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      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




LONG TERM...Staarmann
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