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Area Forecast Discussion

738
FXUS62 KGSP 302059
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
459 PM EDT THU JUN 30 2016

.SYNOPSIS...
An upper trough will push a cold front through the region today and
tomorrow.  The front will stall just to the south of the area by
Saturday, but then will lift slowly back north late in the weekend
into the beginning of next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 445 PM EDT...Water vapor imagery indicates a subtle
impulse shifting across the Tennessee Valley and upper Gulf Coast
States. This feature will provide a source of slightly enhanced lift
as it encroaches on our area, where SBCAPE values are analyzed at
1500-2500 J/kg, and DCAPE 800-1200 J/kg. Damaging winds and large
hail are the primary concerns with the storms that develop in this
environment, although torrential rain and frequent lightning will
be noted. Meso models depict evolution similar to that yesterday
evening, when outflows continued to initiate new convection until
a couple hours after sunset. So our revised PoPs will reflect a
peak around that time, and the fact that the models are depicting
best coverage over the ern half of the CWFA.

We will continue the activity into the night time hours, somewhat
similar to Wednesday night, before activity wanes with passage of
the upper air feature and overturning of atmosphere.

Fog and stratus are expected to develop overnight where heavy rain
falls this aftn/evening.

For Friday we have gone with warmer temperatures, per guide,
and limited our thunderstorm chances to a narrow window in the
afternoon, and especially along the less side trough.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 230 PM EDT Thursday: Upper trough axis and surface cold front
will be pushing east of the area as we start the short term. The
frontal boundary will stall to our south on Saturday as the Canadian
upper low lifts northeast and a shortwave pushes off the Central
Rockies into the Central Plains. The surface system associated with
the Plains shortwave will stretch across the Ohio/Tennessee Valleys,
merging with the stalled Southeast front, and providing focus for
convection to pick back up again through the short term as flow
aloft transitions to zonal. The boundary will slide slowly back
north as the Plains shortwave pushes east, with modest instability -
800-1200 J/kg sbCAPE - returning to the area Saturday. Should see a
diurnal trend through Saturday night, but with the Plans shortwave
moving into the mid-Mississippi Valley on Sunday, should see an
enhancement to the diurnal pops for Sunday afternoon, with likely
pops over the mountains and healthy chance elsewhere. High temps
through the short term should be a couple of degrees above seasonal
normals, with a larger departure for overnight lows where the
increasing moisture will not allow for much of a cool-down overnight.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 300 PM EDT Thursday: Zonal flow will continue across the
Ohio/Tennessee Valleys as a subtropical ridge over the western
Atlantic continues to build west toward FL as the shortwave
continues to work its way east up the Ohio Valley. Several
differences continue in models` handling of this shortwave with the
GFS a little more robust especially with the associated surface low.
Should see a fairly significant increase in convection for
Independence Day. Along with the decent instability (sbCAPEs between
1000-2000 J/kg), we have some minimal low-level shear as well which
may help to organize convection. Overall and unfortunately, it looks
like a pretty wet and occasionally stormy day/evening, so residents
of the western Carolinas and northeast Georgia may want to be
prepared for impacts to Independence Day festivities.

The wave pushes east on Tuesday, with the ECMWF keeping an open wave
and pushing it offshore early in the day, but the stronger GFS
closing it off and not pushing it through for another 24 hours.
Quite a bit of uncertainty here obviously but since the ECMWF keeps
a trailing front across our area anyway, both have similar sensible
weather impacts with enhanced diurnal convection continuing through
mid-week. As would be typical with enhanced summertime convection,
heavy rain and at least isolated severe storms will be possible.

The subtropical ridge continues to build westward, with intermittent
shortwaves riding along the northern edge of the ridge. Differences
between the operational guidance increase through the middle of next
week so have trended close to climo on pops, but with a slight
increasing trend for temperatures, rising into the mid-90s, as
thicknesses increase.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
At KCLT and the SC Sites: Judging by the various CAM models we
have retained thunderstorm chances into the CLT airfield during the
evening. This is trying to follow large scale features/development,
and small scale interactions. Since ceilings are near MVFR levels,
it is possible that tendency of bouncing in and out will continue
through the evening. We would expect greater restrictions to
ceilings and visibilites with storms near the airfield. We have
mentioned some variable gusty winds to take into account current
active situation.

Any stratus and fog should lift to low VFR ceilings Friday morning.

For the remainder of our TAF sites, the biggest difference is
in the timing of convection, arrival and/or development. We have
followed continuity with lower ceilings at sites which were not
yet mixed.  Otherwise would expect potential thunderstorms with
reduced ceilings and visibilities across the board.

Outlook: Diurnal convection expected Friday afternoon and Saturday.
Another series of fronts, and potential weak low pressure systems
riding along the fronts, appears on tap for Sunday through Tuesday.
This period may offer an enhanced thunderstorms possibilities.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High  98%     Med   74%     High 100%
KGSP       High 100%     High  96%     Med   69%     High 100%
KAVL       High  98%     High  91%     Med   76%     High 100%
KHKY       High 100%     High  98%     High  93%     High 100%
KGMU       High 100%     High  96%     High  84%     High 100%
KAND       High 100%     High  95%     Med   73%     High  87%

The percentage reflects the number of guidance members agreeing
with the schedule TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...TDP
NEAR TERM...TS/Wimberley
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...TS/Wimberley



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