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Area Forecast Discussion

FXUS62 KGSP 292025

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
425 PM EDT MON AUG 29 2016

A weak tropical system will approach the North Carolina Outer Banks
tonight and tomorrow before moving back out to sea on Wednesday.
A cold front will approach the region from the north Wednesday night
with another tropical system emerging from the Gulf of Mexico on
Thursday. This system is expected to remain just to our south and
move offshore over the weekend.


As of 425 PM: Water vapor imagery shows several tropical features in
the western Atlantic and Gulf of Mexico. The GSP forecast area
appears to sit between all of them. A break in the large ridge of
high pressure, from Missouri to Bermuda, was noted off the North
Carolina coast - via aforementioned water vapor imagery.

An easterly flow was pushing bands of mid and high level cloudiness
west/southwest, into our region, which should continue for the rest
of the afternoon and tonight. Meanwhile an upper low was spinning
off the SC/GA coast, sending moisture to the northwest. Perhaps it
is this feature which has slowed the overall drop in dewpoints,
especially in our southern areas. SB capes are running higher than
model guide, but have kept isolated convection limited to the far
southern CWFA where chance is best.

The second area of potential precipitation for the rest of the day
would be the high terrain along and near the TN border. We have
maintained continuity with isolated convection there into early
evening. DCAPE meanwhile is running on the low side, which should
keep a bit of a lid on strong convection.

Valley fog and some stratus should once again be noted in those
locations of western NC late tonight.

On Tuesday, as lower theta e air continues to advect into our
forecast area, any precipitation prospects should be minimal. We
will go ahead with below climatology POP values in the NC mountains
during the late afternoon hours.

Despite the clouds, temperatures continue to edge up. We plan to
follow the suite of temperature guide tonight, and then perhaps a
degree or two (above the coolest high temperatures Tuesday).


As of 200 pm EDT Monday:  By Tuesday evening, tropical depression 8
will be moving northeast of the Outer Banks and well outside of
having any direct impacts on the GSP CWA.  Meanwhile, tropical
depression 9 will gradually organize over the Gulf before tracking
across northern Florida late on Thursday.  9 is also not expected to
have direct impacts on the CWA, being too far south and eventually
southeast of the area; at least through Thursday.  POPs, though,
will increase Wednesday and Thursday as deep upper trough over the
northeast CONUS with a surface cold front approaches the area on
Wednesday and Thursday with a FROPA expected around 18Z on
Thursday.  FROPA will bring a significant chance for showers
Thursday afternoon through Friday morning, with some showers
possible Wednesday afternoon over higher terrain in advance of the
system.  Airmass is dryer than recent weeks and we will see CAPE
below 1000 j/kg at most Tuesday and Wednesday afternoons, and precip. amounts
are not expected to be particularly generous.  Front is followed by
significantly cooler and dryer conditions leading into the end of
the week.


As of 210 PM EDT Monday, the medium range fcst picks up at 00Z on
Friday with a positively tilted upper trof axis passing to our
north and a very steep upper ridge spreading over the central
CONUS. In addition, a tropical disturbance that is currently
located north of Western Cuba is expected to be moving across
Northern Florida by early Friday. As we move into the weekend,
the trof axis will translate offshore while the upper ridge
spreads farther east eventually encompassing the eastern half
of the CONUS.

At the sfc, a tropical low associated with the upper lvl disturbance
mentioned above is expected to be moving over North Central Florida
and then off the southeast coast on Saturday. The long range models
appear more consistent with the system overall, however the ECMWF is
still quite a bit faster moving the low off the southeast coast over
the weekend compared to the GFS. The Canadian model remains the farthest
west and slowest wrt the storm track. Regardless, by early Sunday all
the models agree that the low will be moving well offshore and Canadian
high pressure will spread back over the region and persist into early
next week. As for the sensible fcst, the guidance has been trending
drier overall with most of the precip associated with the tropical
system likely remaining to our south and east. The best chances for
widespread precip will be early Friday over the SE zones with only
scattered slight chance POPs for Saturday. The rest of the period
should be dry. Flooding should not be a concern over the CWFA with
total QPF on Friday expected to be less than 0.5 inches. Temps will
start out near or slightly below climatology on Friday and remain
in that range for the rest of the period.


At KCLT: Mid and high level cloudiness will continue to advect
west/southwest across the site right through Tuesday. This is all
tied into the tropical feature off the North Carolina coast.
Meanwhile, dewpoints have been slower to drop which has allowed a
fair amount of cumulus clouds today. They should linger through the
afternoon before dissipating this evening.

VFR conditions should persist Tuesday, with waves of clouds moving
through from time to time. NE surface winds ( on average ) should be
the rule into Tuesday.

Elsewhere: Mostly VFR conditions this afternoon and tonight with a
few exceptions. Most of the convection however should remain south
of all sites. We have beefed up the late night fog at AVL with
nearly calm winds, and will follow persistence.

Outlook: We will remain in-between many systems surrounding the
sites Wednesday, with convection tied into mostly higher terrain. A
cold front will enter the region Thursday and Thursday night, with a
potential uptick in showers and thunderstorms. Depending on the
track of any of the various tropical features, we might be favoring
a drier weekend forecast.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
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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