Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 200558
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
158 AM EDT Fri Apr 20 2018

.SYNOPSIS...
Dry and cool high pressure will linger atop the region into Saturday.
Ahead of developing low pressure, moisture will return to the area
on Sunday, with unsettled weather continuing into early next week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 145 AM Friday...we are settling in for a quiet overnight across
the region. With clear skies and persistent NLY flow, temps have been
falling a little faster than fcst. If winds can remain light enough thru
the mid-morning, then the Frost Advisory could work out well. The Freeze
Warning should pan out for the higher terrain.

Otherwise, no clouds are fcst except for a few high cirrus breaking thru
the ridge axis. A decent airmass mix will accompany the 1036 mb high and
with weakening flow good rad cooling conds will be had...with mins
reaching below freezing across extreme NE GA and the srn/cent NC
mtns. So...the freezing warning still looks good in this area. The
WI.Y across the nrn NC mtns will allowed to expire on time later
this afternoon as the p/grad begins to loosen and mixing is reduced.
Still, there will be gusty conds in those locales into the overnight,
yet not stg enuf for a NPW mention. Across the NC Piedmont, low temps
will reach frost levels...however winds and sfc tdd/s are too suspect
to expect much more than patchy frost and a frost adv will not be issued.
All areas outside the mtns reached fire danger criteria this afternoon
as gusty winds combined with low RH values and persisted for several
hrs. Surface winds will be lower on Fri...so not expecting fire-wx
concerns outside of NE GA where low RH is the only wx criteria needed
for a FDS. Max temps will remain a little below normal Fri as n/ly flow
reinforces a llvl thermal trof...but all in all a nice spring day is
in store.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
As of 235 PM EDT Thursday: The weekend weather looks like it is
shaping up to be a lesson in taking the good with the bad, or
vice-versa. We could have some frost across the NC moutains and
northern foothills early Saturday morning as high pressure remains
overhead. Saturday should be another sunny and dry, but cool,
day as a piece of the surface high moves slowly offshore. Most
people will probably think it a fantastic Spring day. Changes will
start taking place Saturday night, however, as an upper low moves
out over the srn Plains. An upper ridge axis will move overhead by
daybreak Sunday while the split flow pattern aloft holds the center
of a parent surface high over the Great Lakes. The stage will be
set for the development of cold air damming by Sunday afternoon
as moisture returns on a low level southeasterly warm advection
flow over the top of a drier northeasterly sfc wind, while upper
divergence/diffluence and mid/upper dpva ahead of the approaching
upper low spread overhead by the end of the day. Isentropic lift
will increase in the afternoon which should allow for light precip
to break out from SW to NE, first near the Blue Ridge Escarpment/Srn
mountains of NC, then expanding from there. The wrn Piedmont may
remain dry, as the NAM appears to be developing the precip too
fast. Temps should be held in check with the increasing cloud cover
and precip development...perhaps in the mid 60s for highs...but
if the precip develops early in the day this could be as much as
ten degrees too warm. Initial precip amounts should be light.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 250 PM EDT Thursday: Guidance remains in general agreement
through the medium range, but continued run to run inconsistencies
make the details difficult to pin down. As an example the 00Z ECMWF
was slower than the 12Z GFS but the 12Z run has sped up closer to
the GFS. Track differences are noted below. An upper low crosses the
Lower MS Valley and moves into the TN Valley on Monday. The low then
weakens and drifts north to the OH Valley on Tuesday before being
absorbed by the upper trof developing as yet another upper low dives
into the Mid-South. This low moves into the Southern Appalachians
Wednesday before moving east of the area Thursday. The surface low
associated with the first upper low moves through the Gulf Coast
states Monday bringing strong isentropic upglide and copious
moisture into the area. The upglide and moisture continue Monday
night then taper off Tuesday as the low moves to the Carolina coast.
High pressure sets up in a cold air damming pattern Monday and
lingers Tuesday making for a cold, rainy, and windy couple of days.
That said, the GFS is now farther north with the low even taking on
more of a Miller B pattern while the ECMWF keeps it more of a Miller
A. The GFS would indicate the possibility of some instability
forming along the wedge boundary as it drifts into the southern
portions of NE GA and the Upstate. The ECWMF keeps the area stable.
Have increased lows and kept highs on the cool side decreasing the
daily diurnal trend typical of cold air damming. In fact, my highs
may not be cool enough. Precip amounts from 1 to 3 inches look
likely but remain spread out over a couple of days. The GFS would
indicate some QLCS potential Monday, but the ECMWF does not.

Precip chances taper off Wednesday as the upper low weakens and the
surface low pulls northeast away from the area. Highs warm a little
as precip ends and damming high weakens. However, they remain below
normal. A cold front moves through during the Thursday time frame as
the second upper low swings across the area. Forcing and moisture
are not as great with this system but a chance of showers will
continue. Temps will warm to near normal for Thursday.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: expect VFR conditions thru the 06z taf period
with dry high pressure gradually spreading over the region from the NW.
With the dry airmass in place, cloud cover will be limited to only a
few high clouds at most. Thus, the only concern will be winds. They
should weaken a bit more thru the early morning, especially over KAVL,
and remain out of the N to NNE in the 4 to 7 kt range today. KGSP, KGMU,
KAND, and KHKY will likely become light and vrb this afternoon with KCLT
and KAVL doing so later on tonight. No significant gusts are expected
thru the period.

Outlook: Broad and dry high pressure will linger through Saturday.
Restrictions may develop late Sunday into Monday as a warm front
lifts northward over the area, bringing deeper moisture up from the
Gulf of Mexico.

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

&&

.FIRE WEATHER...
Cooler and much drier conditions will continue through the end of
the work week. Winds will decrease on Friday below critical
thresholds but will have to be monitored, since RH values will
remain very low.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Freeze Warning until 9 AM EDT this morning for GAZ010.
NC...Freeze Warning until 9 AM EDT this morning for NCZ048-051>053-
     058-059-062>065.
     Frost Advisory until 9 AM EDT this morning for NCZ035>037-056-
     057-068>070-072-502-504-506>510.
SC...None.

&&

$$
SYNOPSIS...CSH
NEAR TERM...ARK/JPT
SHORT TERM...PM
LONG TERM...RWH
AVIATION...JPT
FIRE WEATHER...PM



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