Area Forecast Discussion
Issued by NWS Greer, SC

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258
FXUS62 KGSP 260603
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
203 AM EDT Mon Jun 26 2017

.SYNOPSIS...
Dry and cool air will continue to spread in from the northwest over
the forecast area through much of the week as Canadian high pressure
remains to our north. As the high moves offshore, moist southerly
flow will return toward the end of the week through the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
As of 145 AM EDT: the overnight should remain quiet with only a few
high clouds streaming overhead and some lingering stratus moving
over the far SE zones from the SW as the weak frontal bndy remains
just to our SE. Otherwise, a broad upper trough currently covers the
eastern two thirds of the CONUS with very steep upper ridging over
the west. Upper level RH trends indicate some drying as the jetlet
shifts slightly east, so these clouds are expected to gradually
become more patchy with time. Patchy fog near rivers, lakes, and
bodies of water will remain possible but should be fairly shallow.
A weakly reinforcing cold front, with little to no moisture, will
move through the region on Monday to bring in slightly cooler and
drier air. Maxes will be about a category below climo Monday
afternoon.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
As of 230 PM EDT Sunday:  The short term fcst period kicks off
on Monday evening amidst broad H5 troffing across much of the
east/central CONUS, while a series of shortwave impulses pass
through the mean flow aloft.  At the surface,  a weak/dry cold front
will be making its way into/through the high terrain of western NC
as high pressure slides east across the TN Valley.  Given the drier
nature of this fropa as well as a lack of any sig shortwave energy,
will keep the fcst dry through the overnight hours.  However,
by early/mid Tuesday afternoon a slightly more potent shortwave
will accompany another reinforcing cold front, which will dive
through the OH valley into east TN/KY then western VA/WVA by
Tuesday evening.  Given improved convergence along the front as
well as weak upper forcing thanks to the shortwave, think convection
will be possible across the aforementioned areas, eventually moving
at/into western NC by late day Tuesday.  Therefore the fcst will
feature slight/chance pops across portions of western NC with the
highest pops being across the mtns along/north of I40.  Beyond that,
broad surface high pressure will consume the fcst area for Wednesday
leading to pleasant conditions.  Temperatures/dewpoints will be the
primary highlight of this fcst period as highs top out each day
nearly 6-8 degrees below normal, with dewpoints in the lower/mid
50s yielding low RH values.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 155 PM EDT Sunday: No sigfnt changes needed to the going fcst.
The models continue to show the transition from a unseasonal trof /
Canadian sfc high config into more of a normal summertime pattern.
There shud be enuf llvl moisture adv for mtn top convg shrs/tstms
Thu afternoon but coverage will be limited as upper heights rise and
a subtrop ridge noses in from the east. Things become more
interesting Fri thru the period as sfc-based instability increases
and easily breaks a weak cap each afternoon allowing for stronger
diurnal convection with better coverage...mainly across the higher
terrain Fri. Mid level LRs increase to arnd 6.5 C/km on Sat associated
with an incoming h5 s/w which will develop stg/svr activity over the
mtns/fthills spreading east across the piedmont regions thru the
late afternoon and evening. A cold front approaches the FA late Sat
and there is decent agreement in the guidance to suspect the front
will push into the FA and become quasi-stationary Sun. Thus...above
normal coverage will be had with thunder activity developing within
a continued unstable atmos. Max temp will begin the period a little
lower than normal and increase to near or just above normal by the
weekend. Mins will also rebound to normal levels in an increasingly
moist environ.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: expect VFR conditions to persist over the
fcst area thru the taf period. A persistent area of enhanced upper-
level divergence to our north will continue to bring a few high
clouds over the region thru the overnight and into the morning. In
addition, some sct stratus in the 4 to 6kft range continues to
stream across our southern zones as deeper lyr moisture and a weak
frontal bndy linger to our southeast. Most of this cloud cover
should dissipate over the next 4 to 6 hrs as the deeper moisture
gets pushed farther south. Winds will remain light and NLY through
most of the period. More of the guidance is now backing winds to
more of a WLY direction by the late afternoon at all sites except
KAVL in response to a weak lee trof developing briefly. I included
this wind shift in the TAFs, however confidence is not very high.

Outlook: Light winds and VFR conditions should continue through mid
week. Moist, SLY return flow will return around the offshore ridge
by Thursday.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
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...SBK
NEAR TERM...JPT/Wimberley
SHORT TERM...CDG
LONG TERM...SBK
AVIATION...JPT



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