Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 270552
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
152 AM EDT Tue Sep 27 2016

.SYNOPSIS...
A cold front will cross our area tonight and be near the Carolina
coast by Tuesday evening.  An upper level low will drop south into
the Ohio Valley by Wednesday and linger over the Central
Appalachians through the end of the week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1030 PM, band of heavy rain showers and storms has pushed east
of I-85 late this evening, although a fairly large area of moderate
rain has developed upshear of the leading convective line. Thus,
likely to cat pops will be maintained in these areas through the
next 2-4 hours. Fortunately, the heavier rates have pushed south of
the part of Charlotte metro that experienced flooding this morning
with little additional fanfare. There still could be some problems
on the south side of the metro area, where FFGs are closer to 2
inches, but rainfall rates are expected to continue gradually
diminishing within the band. Overall, mainly just a chance for the
parched Piedmont to receive some beneficial rainfall.

The cold front remains draped from East TN into the central
Appalachians this evening, and is only expected to make minimal
progress into the forecast area over the next 24 hours. There isn`t
a whole lot of support for additional development along the front
overnight, as instability is minimal and there is little synoptic or
mesoscale forcing. Mesoscale models are not at all excited about
additional development, although the HRRR develops some widely
scattered activity near the TN border by 06Z. Small chances pops
will be maintained in those areas through the overnight, with slight
chances at best elsewhere.

Otherwise, over the next 24 hours, big-picture-wise a large
mid/upper low is expected to slowly drop down from western Ontario
to the upper Great Lakes, which will bring mid/upper troffing down
across the western Carolinas. This should drive a surface cold front
from the TN valley eastward across the Srn Appalachians tonight and
Tuesday morning. The front will probably get hung up across the mtns
thru most of the day on Tuesday. Weak upper divergence will get
strung out across the region tonight and Tuesday as the right
entrance region of the upper jet moves overhead, but mid-level
forcing is not that impressive. Most of what the front does will be
the result of deep convection firing along and ahead of the feature
this afternoon and evening, and then the weak forcing overnight. The
guidance suggests holding onto a likely precip prob mainly out
across the NC foothills and wrn Piedmont into the overnight hours.
Min temps tonight should be mild. On Tuesday, with the front in our
midst, precip chances should ramp up especially over the eastern
zones where a likely was included. Temps will be at or above normal
again.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
As of 245 PM Tuesday: Showers and thunderstorms will be scattered
along and southeast of Interstate 85 Tuesday evening as the front
slowly drops south. This activity will slowly diminish but may
linger into Wednesday morning. Most of Wednesday should be dry as
cooler air moves into the region.

A fairly potent upper level low pressure system will drop southeast
across the Ohio Valley and central Appalachians impacting the area
Wednesday night and Thursday. Several disturbances will swing around
the parent low bringing rainfall to the area. The highest chance of
rain will be in the upslope areas of western North Carolina while
the lowest chance will be in northeast Georgia and upstate South
Carolina where downsloping low level flow will exist. All locations
will be cooler as the impacts of the low translate across the area.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 315 PM EDT Monday...An upper low is expected to be over
Bristol TN Thursday evening then lift north to eastern OH Friday
evening.  The GFS forecast has been accepted as the better
performing operational model. The ECMWF is better today but still
slower in its evolution of the cut off closed low lifting out and
departing New England.  With the lower atmospheric thickness values
associated with this upper low and more cloud cover Thursday night
into Friday, this will keep temperatures several degrees below
normal. Very light rain amounts are possible across the NC Mtns and
north of I-40 Thursday evening then becoming increasingly limited to
the TN border areas until Friday evening when it goes away to the
north of our forecast area.

The closed and cut off upper low will begin to open to the westerly
flow at the north end of the Great Lakes on Saturday. The low will
fill and become absorbed near Montreal Sunday night. We will be at
the southern end of a large area of surface high pressure Sunday
into Monday. The GFS has the high centered over north central Quebec
at 12Z Tuesday ridging down across our area. The orientation of the
low level wind flow with this high may produce upslope wind by
Monday night into Tuesday which may result in light rain in the Lake
Jocassee to Tryon to Lenoir areas.

Temperatures will certainly be several degrees below normal Friday
then slowly rise to near normal as the low moves away from our
region over the weekend. By Monday, temps may even be a little above
normal since the high may not be strong enough and far enough away
to have minimum influence toward wedge conditions.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
At KCLT: Convection has almost completely moved out of the area with
just some lingering -SHRA. This will continue to wane over the next
hour, after that the concern will be development of restrictions.
Expect at least MVFR to develop shortly, lowering to IFR and
possibly LIFR. Should see slow improvement after sunrise, but with
the approach of the front expect to see another round of TSRA this
afternoon. Best chances look to be between 22-00z tonight and ended
up with short prevailing TSRA but will continue to reevaluate that
with new data. Winds remain generally S but with the front
approaching may see brief backing ahead of it, and then just beyond
the end of the period winds will begin shifting W.

Elsewhere: Convection has moved out of the areas, though another
line is developing along the mountains with the front that may
impact KAVL overnight. Bigger concern will be widespread IFR
conditions, with confidence not quite as high across the Upstate
TAFs as for KAVL/KHKY. Improvement after sunrise and with the front
moving into the area should see another round of SHRA/TSRA, and
handled this with a combination of PROB30/VCTS/prevailing TSRA.
Mainly S winds slowly veering SW, and for KAVL/KHKY should see winds
shift NW toward the end of the period.

Outlook: Cold front will slowly cross the region today. Dry high
pressure builds in slowly behind the front on Wednesday, which
should bring VFR conditions in most places through the end of the
week.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       Med   75%     High  80%     High 100%     High  96%
KGSP       Low   57%     High  84%     High 100%     High  96%
KAVL       Med   67%     Med   77%     High  97%     Med   69%
KHKY       Low   56%     Med   75%     High 100%     High  98%
KGMU       Low   55%     High  82%     High 100%     High 100%
KAND       High  91%     High  89%     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...JDL/PM
SHORT TERM...SW
LONG TERM...DEO
AVIATION...TDP



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