Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 252111

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
511 PM EDT Thu May 25 2017

A large low pressure system will lift northeast of the area tonight
allowing drier air to overspread the region and linger into early
Saturday. Moisture and unstable conditions will return to the region
over the weekend, ahead of a slow moving cold front.


As of 500 PM EDT Thursday: Showers under the passing upper trough
continue to impact the I-40 corridor and nearby locations, with less
forcing and moisture farther south. Cold temperatures aloft will
keep steeper lapse rates and 500+ J/kg sbCAPE going along and east
of I-77 through sundown. Some of the stronger cores could have small
hail, as we have seen earlier. Other showery elements may move down
across the nrn mtns and nrn foothills as they rotate around the
upper low, seen in the water vapor imagery moving into WV. Temps
should remain seasonally cool.

Over the next 24 hours, our weather should continue to unwind. The
upper low will move past across the Mid-Atlantic region tonight.
Additional low level moisture and some light precip will come down
across the northern part of the fcst area, with the NW flow forcing
additional showers along the TN border into the evening hours. The
model guidance shows this gradually drying up, with precip ending by
around midnight. There is some concern for strong wind gusts across
the higher terrain as the guidance shows greater than 50kt flow at
850 mb coming around the bottom of the upper trof tonight. However,
the boundary layer remains shallow, and then decouples and keeps
that stronger flow from reaching the sfc in model fcst soundings.
Low temps will be below normal tonight, but not exceptionally cold.
On Friday, the cyclonic flow aloft will gradually be replaced by a
flat upper ridge building in from the west. This ridge will support
weak high pressure moving over the Southeast. Sunny sky should
prevail that will result in a very nice and dry late Spring day with
high temps just above normal.


As of 230 PM Thu: Zonal mid level flow will be in place across the
region through this period. Low level moistening will be occurring
on Friday night and Saturday. A frontal system will move into the
Tennessee Vally on Saturday allowing some shower and thunderstorm
activity to move into the mountains Saturday afternoon and Saturday
night. Another round of storms should impact most of the forecast
area Sunday afternoon.

Instability will be rather high on both Saturday and Sunday
afternoons. Some storms could be rather strong especially if they
are able to organize in the westerly flow.


As of 235 pm EDT Thursday: the extended fcst picks up at 00z on
Monday with flat upper ridging over the southeast and another
broad upper trof digging down over the Western Great Lakes. The
trof is slow to move eastward and is not expected to move over
the fcst area until late Tues into early Wed. The long range models
have the trof axis centered to our north by Wed, however most of
the energy associated with the trof remains to our north. As we
move into Thursday, the trof lifts farther NE and heights begin
to rise a bit. At the sfc, a cold front will move thru the CWFA
on Monday and stall out just to our SE by early Tues. The front
lingers over the region until another, more robust cold front pushes
thru the fcst area on Wed into early Thurs. As for the sensible fcst,
no significant changes were necessary. We still have solid chances
for convection on Monday, and slight to solid chances on Tuesday
thru Thursday with the highest POPs generally over the higher
terrain. Temps will start out just above climatology and cool on
Tuesday to right around normal. They are expected to remain near
normal for the rest of the period.


At KCLT and elsewhere: VFR through the period. SCT/BKN clouds
continue to develop generally with bases in the 040-050 range as
colder air aloft moves overhead. Think SCT will prevail with
temporary BKN conditions possible at the NC TAF sites. A few showers
may develop, more likely over the mtns near the TN border, and over
the wrn Piedmont of NC. The clouds should diminish in coverage with
loss of heating, and any remaining showers after sunset should be
confined to the TN border area. Wind will remain WSW with occasional
gusts through sunset, then diminishing overnight as the boundary
layer decouples and weak high pressure ridges up from the S. On
Friday, only sct cirrus. Wind will be SW or WSW again outside the
mtns, with occasional gusts beginning midday as the boundary layer
deepens again with heating.

Outlook: Continued VFR Friday afternoon and night, and into the day
on Saturday. Thunderstorms and associated restrictions may develop
across NC Saturday afternoon, but will be more likely Sunday.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
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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