Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 272338
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
738 PM EDT Sat May 27 2017

.SYNOPSIS...
Warm and humid air will remain over our region through at least
Monday, as high pressure settles east of the Florida coast. A cold
front will slowly approach from the northwest, but will struggle to
push through the area during the middle of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 725 PM EDT: A severe thunderstorm watch has been posted for
most of western North Carolina as upstream convection is drawing a
bead on western NC and additional discrete convection will likely
form over the higher terrain and quickly advect out over the
piedmont through late evening. Corfidi vector steering flow appears
to mainly impact western NC and convective inhibition remains fairly
decent farther south and east. Damaging straight line winds and
large hail due to the steep lapse rates will be the main threats
with this first round.

A second round is possible with an MCS developing over central and
western TN later this evening that should run across the far
southwest mountains and northeast GA overnight/upper Savannah river
area overnight. The forecast has been updated accordingly for higher
northern tier PoPs, with a severe thunderstorm mention this evening,
and then higher southwest sections PoPs for the overnight hours.

The forecast area will remain solidly in the MCS tracks on Sunday
from convection developing from the west in the unstable elevated
mixed layer. Shear will remain more than adequate for
organized/severe convection, with perhaps a better potential for
rotating cells in areas of enhanced low level helicity near the
boundary. Thus, all manner of severe weather is possible on Sunday.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 230 PM EDT...This portion of the forecast becomes very fuzzy
with multiple embedded ripples of vorticity (some convective feed-
back) moving through our region. Although the models offer various
output in this section of the forecast, we will play one outgoing
shot of convection Sunday evening, then lower POPS, with another
shot of energy perhaps reaching our western forecast area (FA)
Monday morning with another uptick in POPS western sections.

The evolution of additional thunderstorms Monday will be somewhat
dependent on whether the early morning convection (if it happens),
tempers the atmosphere. On the other hand we still have a broad
southwesterly flow aloft in place, due to the large upper low north
of the Great Lakes, and spokes of energy rotating through. Also a
weak surface wind shift dropping south into the area, helping to
provide a focus. Considering the unstable nature of the atmosphere
we will continue with medium range chances, and future forecasts may
be able to focus in on additional details.

For Monday night and Tuesday, with the flow aloft southwesterly it
is hard to imagine the front/boundary pushing through our FA, unless
cold pool driven. Therefore we will bring POPS down Monday night,
and then run lower chances on Tuesday, especially south of I40.
There actually may be a series of wind shift lines to cross the area
through Tuesday.

Since we note a downward nudge in the thermal profile Tuesday, we
will back readings off a few degrees compared to Monday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 210 PM Saturday: A closed upper low located just north of the
Great Lakes will rotate east but then return to just north of the
Great Lakes next weekend from Hudson Bay. This broad feature creates
a big trough over the east.  Meanwhile, at the surface, a stalled
frontal boundary stretches from Texas to the Carolinas through the
second half of the week except for Thursday when high pressure
coming down from near the Great Lakes pushes the front south of our
area but only for about a day. Shortwave energy and waves of low
pressure will pass across the deep south increasing the chance of
showers and storms Friday and Saturday.  Severe threat should be
quite low.

Expect temperatures to be near normal through the medium range
period.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
At KCLT: Timing of the convection developing from the west still
looks good for 02Z to 06Z, with TEMPO thunder and associated W to NW
flow gusts. There may well be a lull overnight and then the region
will remain in the tracks of upstream MCSs through Sunday afternoon.
Will time the second round with a PROB30 18Z to 24Z. Expect mainly
southwest flow with low end gusts during mixing away from
thunderstorms, and then robust WNW gusts during thunder.

Elsewhere: Several rounds of thunderstorms will be possible at the
mountain and foothills TAF sites as upstream convection rolls
through this evening, overnight, and likely again on Sunday
afternoon. Will handle the first round with TEMPO TSRA at KAVL and
KHKY, with mainly just VCTS at the Upstate TAF sites. The second
round moving across the SW NC mountains and NE GA overnight will
probably miss the Upstate sites just to the southwest. Will feature
a PROB30 for mainly Sunday afternoon for round three of MCS
activity. Expect mostly SW flow with low end gusts during mixing,
except more robust NW gusts with thunderstorms.

Outlook: Thunderstorms and associated restrictions, mainly of the
afternoon/evening variety, as well as the potential for areas of
morning fog and/or low stratus will continue through at least the
middle of next week.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
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:

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...DEO
NEAR TERM...HG
SHORT TERM...TS
LONG TERM...DEO
AVIATION...HG


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