Area Forecast Discussion
Issued by NWS Greer, SC

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779
FXUS62 KGSP 250540
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
140 AM EDT Thu May 25 2017

.SYNOPSIS...
A cold front will push east of the area overnight, leading to
gradual drying. An upper level low pressure system will cross the
region through Thursday, with stronger drying developing from the
west Thursday night through Saturday behind the passing system.
Moisture and instability will then slowly build over the southeast
from Sunday through early next week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1030 PM EDT: All watches are off the board late this evening
as any residual convective threat over the I-77 corridor is limited
to a few cloud to ground strikes and briefly gusty winds, while the
hydro threat continues to diminish as the heavier precip rates move
east.

Still expect the deep upper trough west of the mountain chain to
push in from the west overnight and cross the region on Thursday.
The convection allowing models do a decent job at depicting the
current activity under the trough axis across Alabama, and they have
this dissipating as it moves east across GA overnight. Isolated
showers could survive into the western mountains in moist westerly
upslope flow and possibly into the upper Savannah river valley -
where PoP will be featured. Otherwise, the bulk of any activity
under the coldest part of the passing trough will be daytime
Thursday, where high end chances will be featured along the I-40
corridor. Max temps will remain below normal on Thursday.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
As of 230 PM EDT Wednesday: The sharp trough, and associated upper
level low pressure system, we have been dealing with will shift to
the east of our forecast area (FA) Thursday evening. The last of the
convection should be ending Thursday evening in the NC mountains.

As the upper low lifts northeast into New England we will remain in
a broad northwest flow aloft. Meanwhile high pressure from the Gulf
of Mexico will build north into the Tennessee Valley. Moisture will
be on a downward swing, and with the high pressure system close
enough, we should have a dry Friday.

The upper flow will deamplify Friday night and Saturday, with
ripples of energy riding east/southeast from the Mississippi Valley
into parts of the southeast. At the same time, a weak frontal
boundary will try to drop south (from Kentucky and Virginia), but
will encounter the southern end of the westerlies and halt.

Nevertheless there appears to be a boundary of sorts (depending on
model preference) which allows some moisture to pool and
precipitation to develop. The GFS is the fastest, with the NAM and
European Models slower. Since the Gulf of Mexico is cutoff from this
scenario, we have sided with the slower precipitation guide Friday
night, limited late in the NC mountains. We will have chance, or
small chance, pops Saturday, perhaps reaching down to near the SC/NC
state line and NE Georgia.

Interestingly the SB Capes from both the GFS and NAM are hefty for
Saturday. However, a stout cap is in place. Therefore without a
strong trigger it might be difficult to realize the instability.

In the temperature department our thermal profile signals a warming
trend into Saturday, which we will follow.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 215 pm EDT Wednesday: the extended fcst picks up at 00z on
Sunday with flattening upper ridging over the southeast and another
broad upper trof digging down over the Western Great Lakes. The long
range models still have some lobes of mid to upper lvl shortwave
energy passing just to our north on Sunday, however the main trof
will be slow to progress eastward and isn`t expected to move over
the fcst area until late Tues into early Wed. At the sfc, a cold
front will approach the CWFA early Sunday but is not expected to
move thru the CWFA until Monday. It appears to become stationary
just to our SE by early Tues and lingers over the area until another,
more robust cold front pushes thru the CWFA on Wed into early Thurs.
As for the sensible fcst, no significant changes were made. We still
have solid chances for convection on Sunday and Monday, and slight
to solid chances on Tuesday and Wednesday with the highest POPs
generally over the higher terrain. Temps will remain above climatology
thru the period with a slight cooling trend towards the end of the
period.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Front is working its way across the area at
TAF time, with some lingering convection/SHRA toward KCLT. Drying
moving in from the west, but should see some TEMPO MVFR/IFR for all
but KAND for the next hour or so, but with rapid improvement
thereafter. Upper low moves across the area this afternoon and
should see redevelopment of -SHRA mainly to affect NC TAFs; chance
of TSRA too low to mention at this time. Any -SHRA should move out
by mid-late afternoon. SW winds today due to lee troughing for all
but KAVL where NW winds will prevail. Winds will pick up to 10-15kt
with gusts 20+kt especially for Upstate TAFs as gradient tightens
while the upper low moves over. Winds subside overnight with VFR
conditions.

Outlook: The drying trend that starts this afternoon/evening will
continue through Saturday. Moisture will return ahead of the next
front starting Sunday.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       Med   69%     Med   75%     High 100%     High 100%
KGSP       High  87%     High  95%     High 100%     High 100%
KAVL       High 100%     Med   75%     High 100%     High 100%
KHKY       High  87%     High  95%     High 100%     High 100%
KGMU       High  87%     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...JPT
NEAR TERM...HG
SHORT TERM...TS
LONG TERM...JPT
AVIATION...TDP



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