Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 260248

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1048 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 1040 PM EDT: Water vapor satellite imagery shows the axis of
the upper trough moving past the Mid-Atlantic region late this
evening, with deeper layer dry air in place over the western
Carolinas and ridging developing from the west. Regional radars show
just isolated to scattered light rain showers in the increasing
upslope flow over the mountains, with the best coverage over the
northern mountains near the Tennessee line. PoPs will steadily
diminish overnight.

There is some concern for strong wind gusts across the higher
terrain as the guidance shows 40 to 50 kt flow at 850 mb coming down
the back side of the upper trough. However, the boundary layer
remains shallow, and then decouples and keeps that stronger flow
from reaching the surface in model forecast soundings. Any advisory
level gusts should be limited to elevations above about 5000 feet.
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. Other than cirrus,
sunny skies should prevail and 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 conditions will continue through the
period in all but the northwest upslope flow sections of the
northern mountains where lower clouds will linger near the TN border
for a while overnight. Lingering SCT to BKN stratocumulus will
quickly dissipate tonight and leave mainly cirrus the rest of the
period. Gusty winds may persist at KAVL for a part of the overnight,
but largely decouple at the foothill and piedmont TAF sites. Even
the mountain valleys should gradually settle down in the weakening
gradient by daybreak. Occasional gusts may develop again throughout
with mixing on Friday. Expect dry conditions to continue.

Outlook: Continued VFR Friday 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...

            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 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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