Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 231731
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
131 PM EDT Sun Jul 23 2017

.SYNOPSIS...
A cold front will become stationary from west to east across our
region through the middle of the week then dissipate.  This should
result in a little cooler temperature and better chances for rain
over the next few days.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 130 PM EDT Sunday: Convection developing and becoming strong
to severe across the NC mountains. This will form a line and spread
SE across the CWFA this afternoon. Strong to damaging wind gusts
expected as this line moves through.

Temperatures will be hot with humid conditions again today. However,
temps should remain in the mid 90s, so even with less dew point
mixing, heat index values should remain below 105 for the bulk of
the area.

Otherwise...events around the wrn Carolinas have occurred when we
have a few very hot days in a row with limited convection, but then
a subtle change occurs that unleashes pent up energy resulting in
storms more numerous and severe than expected.  This could be one of
those days. If that wasn`t enough, we will have some potential for
bringing an organized convective system in from the WNW later
tonight. Will keep a chance in the fcst overnight to account for
that.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday: a progressive upper trough will deamplify as it
crosses the Appalachians on Monday, then retreating to the New
England coast on Tuesday. At the surface, a cold front is progged to
be draped across the CWFA on Monday, sagging slightly south into the
lower SC Piedmont or the Midlands on Tuesday. Depending on how much
convective overturning occurs on Sunday into Sunday, Monday may end
up being a little less active than the model guidance suggests. The
00z Hires Windows and the NAMnest are now depicting most of the deep
convection off to the east of the area, with only isolated to
scattered weaker activity atop the CWFA Monday aftn. I have lowered
PoPs slightly to trend in this way. However, confidence in the
amount of instability is still low. Temps may also end up being a
tad cooler. However, the 00z MOS guidance has actually trended
warmer than previous runs. In any case, will continue to forecast
highs a category or so above normal.

On Tuesday, the latest operational models now all depict a weak
upper disturbance or possibly an MCV that develops over the lower MS
Valley. This may help enhance convection across the deep south and
to the north along the stalled front. With the overall weak flow
aloft and typical late-July heat and humidity, I expect typical
diurnal convection, expect perhaps a little greater than usual
coverage owing to the lingering front. A small pulse severe threat
can be expected both days.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 330 AM Sunday: The medium range starts out 12z Wednesday with
a weak closed 500 mb low trying to develop INVOF the Carolinas under
a building ridge. By the time the low starts to close off, a
northern stream trough will enter the Great Lakes and should kick
the energy out to the east. This trough will continue to dig along
the East Coast Friday into next weekend. At the surface, a weak low
briefly develops along the stalled frontal zone draped across the
Deep South. This wave be at its strongest during the day on
Wednesday, keeping a light easterly low-to-mid level flow across NC.
With a 1025 mb sfc high over New England and models showing plenty
of clouds and precip across the Carolinas, it almost looks like a
weak cold air damming setup. However, low-level thicknesses do not
suggest true damming. So temps will be slightly below normal, but
not as cold as would be with CAD. PoPs will feature basically a
shotgun CHC for now.

From there, with another upper trough digging in across the eastern
CONUS, expect temps to remain near normal to slightly below. PoPs
will be near climo on Thursday, then above climo for Friday with
another front pushing in from the NW. Depending on exactly where the
axis of the upper trough sets up, the unsettled weather may shift
just east of the area, resulting in a relatively dry weekend.
However, the 00z GFS and ECWMF both keep the trough just enough west
to continue at least a chance for diurnal convection.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Line of convection developing across the NC
mountains and becoming strong to severe. Have gone pessimistic with
the TAFs in response and indicate VRB winds and TSRA in a TEMPO.
Storms could linger a while in the evening outside of the mountains
so have VFR VCTS in place. Guidance not very favorable for
restrictions outside of the mountain valleys overnight, so have
limited them to KAVL. That said, they will be possible as most
locations will receive rainfall. Scattered convection expected
Monday for all but KHKY. SW wind today becomes light overnight, then
W to SW for Monday.

Outlook: Increasing chances of convection expected through the
middle of next week ahead of a series of weakening cold fronts.
Overnight restrictions will continue in the mountain valleys with
chance increasing elsewhere.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
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  94%
KHKY       High 100%     High 100%     High 100%     High  83%
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...ARK
NEAR TERM...PM/RWH
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...RWH


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