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Area Forecast Discussion

FXUS62 KGSP 281713

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
113 PM EDT SUN AUG 28 2016

Surface high pressure will remain over the region early this week. A
frontal boundary will push through by the end of the next work week,
though a lack of moisture will keep rain chances near or below
normal for most of the week. The tropics remain active as we near
the peak of the season...though no systems appear to be a threat to
our area at the current time.


1715 UTC Update: Winds were updated with a blend of the latest NAM
and ADJMAV guidance. Pops and QPF were updated based on radar trends
favoring the southern NC mountains. Sky cover was updated based on
satellite data.

1430 UTC Update: Pops were updated to account for activity in the NC

1230 UTC Update: Sky cover was updated form the latest infrared
satellite imagery. Pops and QPF were adjusted based on sky cover and
radar trends.

As of 650 AM: I will update the forecast to increase coverage of mid
and high clouds across the nrn NC mtns and foothills. Otherwise, the
current forecast appears on track.

As of 325 AM: IR satellite images indicated that a large area of mid
to high clouds will push SW across the region early this morning. MOS and
latest near term guidance indicates fog and low clouds will develop
across the region over the next several hours. However, it appears
that the mid and high clouds will linger over the region longer than
guidance indicates. I will limit mention of restrictive fog and
ceilings to dawn. Drier air under a deep H5 ridge should build SW
across the western Carolinas, as a ridge of sfc high pressure slowly
increases from the mid-Atlantic states. Based on the position and
timing of the drier air, the potential for deep convection across
the foothills and Piedmont appears very low. Lingering moisture
across the mtns and extreme NE GA may support iso to sct
thunderstorms late this afternoon into the early evening. Winds
through today and tonight should remain light from the ENE. Using a
blend of MOS, I will forecast mid 80s within the mtn valleys to low
90s across the Piedmont.

Tonight, the low located between the Carolina coast and Bermuda will
track slow west overnight. GFS and ECMWF indicate that dry air
should remain over the middle of the forecast area. However,
moisture associated with the low should begin to build west across
the eastern Carolinas. I will forecast cloud cover to increase from
the west after midnight. The combination of the dry environment and
little to no forcing should favor dry conditions tonight. Low
temperatures are forecast to range from the mid 60s across the mtns
to low 70s across the Piedmont.


As of 315 AM Sunday, The subtropical ridge will continue to dominate
much of the southern 2/3 of the Conus through the short term. Weak
surface ridging is expected to maintain low level NE flow and a
relatively low theta-E air mass across the forecast area through the
period. Therefore, the diurnal convective cycle looks to be a bit
less active than typical of late summer. The best chances will exist
over the mtns, and across the southeast/southern areas, as moisture
and showers circulating around a weak tropical wave stalled near the
NC coast may make a run for our Piedmont zones, especially late
Monday into Tue. However, chances even in those areas will not be
high, 20-30 percent at best through the period. Temps will generally
be near climo.


As of 320 AM Sunday, the tropics remain quite the challenge for
human and computer forecasters during the medium range. The headline
du jour is that the 00Z ECMWF now carries the disturbance currently
centered north of Cuba into the warm waters of the Gulf by Tue,
where it promptly develops it into a major tropical cyclone just off
the west coast of Florida by the end of the week. Interestingly
enough, the latest GFS is similar to the ECMWF in terms of the track
and timing of this feature. In fact, between about 18Z Thu and 18Z
Friday, both models are virtually identical with surface low
placement. It`s just that the ECMWF is 15-20 mb stronger. Meanwhile,
the Canadian model remains the most consistent model in landfalling
a major cyclone along the Gulf Coast later this week, although the
timing of this has been erratic and the 12Z/27th run appeared to
back away from this scenario.

However, as all this is occurring, heights are falling along the
eastern seaboard, allowing a somewhat modest frontal boundary to
drop toward the Southeast coast by the end of the week. The effect
of this should be to keep any impacts associated with the tropical
cyclone along the coast (the Canadian solution notwithstanding). In
fact, a perfect prog of the ECMWF (ha!), which depicts a hurricane
moving northeast just off the Carolina coast next weekend would
likely result in a subsidence-induced pleasant/breezy late week
across our forecast area. Nevertheless, with such rampant
uncertainty, we opted to make minimal changes to that part of the
forecast attm, allowing the chance pops for convection associated
with the frontal zone to stand. Temps will begin the period a bit
above climo, falling back to near or even below climo in the
vicinity of the frontal zone by the end of the week.


At KCLT and elsewhere: IFR cigs are persisting across much of the
area, but are expected to lift this afternoon. Drier air moving in
from the northwest will not be very supportive of afternoon
convection today or Monday. Winds are expected to favor the
northeast at foothills sites, and the north at KAVL. A guidance
blend only favors a daybreak vsby restrictions at KAVl, with IFR
there. Gudiane does favor a daybreak cig restriction at KCLT.

Outlook: Ridging will persist across the region into early next
week. Convective chances may be limited by sinking air to the west
of a tropical system at the coast. Patchy fog will be most favored
in mountain valleys.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High  94%     High 100%     High 100%     High 100%
KGSP       High  87%     High 100%     High 100%     High 100%
KAVL       High 100%     Low   55%     High 100%     Low   31%
KHKY       High 100%     High 100%     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:






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