Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211836

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
236 PM EDT Mon Aug 21 2017

Typical late summer conditions will persist ahead of an approaching
cold front, which will reach our area Wednesday. A large region of
surface high pressure will then gradually build into the area late
this week through the weekend, bringing unseasonably cool and dry


As of 130 PM EDT Monday:  Although deep ridging prevails this
afternoon across the region, iso/sct shra have developed as
instability peaks with heating.  Giving warm temps aloft, am not
expecting any deep convection, however enough instability is present
to warrant slight/chance pops across portions of the area, maximized
along the highest peaks and ridgetops of western NC.  Latest GOES16
visb does indicate modest cu development across much of the area,
with a minima of sky cover just north of the I85 corridor.  Am still
expecting some mixing to occur, which combined with totality could
yield localized and short term cooling and scting of low cu.
Otherwise, convection across the region will diminish after sunset
with loss of heating, leading into a dry evening.  Guidance
continues to favor abundant BL moisture across the region on Tuesday
morning, with patchy fog possible for any regions that experience
convection this afternoon, yet with the best chances in the mtn
valleys as was the case this morning.  Moving into Tuesday, the
upper ridge looks to weaken a bit as a trof approaches from the
west.  With that, guidance favors convection across the high terrain
once again based on a diurnal trend, with propagation into the
fthills/piedmont possible late in the day.  Thus widespread chance
pops were featured over the mtns, with slight chances spread across
the remainder of the fcst area.  Temperatures through the period
will remain a few degrees above normal.


As of 2:30 PM EDT Monday: The trend Tuesday night will be to allow
diurnal convection to wane early in the evening. We will draw POPS
back to the NC/TN state line toward Wednesday morning ahead of a
slow moving cold front.

The combination of a surface cold front starting to impinge on our
region Wednesday, coupled with deep moisture, instability, upper
level energy and marginal shear, should support rather widespread
convection. We have most POPS in the high chance category or likely.

Because the upper level flow does not attain deep cyclonic flow at
our latitude, the front will start to stall Wednesday night (in a
west to east fashion). This will result in better POPS Wednesday
night edging south into NE Georgia and upstate SC.

The front then moves very slow slowly south, but does not get far
enough away to still impact our region with a chance of showers or
thunderstorms. The best chances will be located across our southern
upstate piedmont.

Another hot temperature day is expected Wednesday, particularly as
the H85 thermal structure increases ahead of the front. Thursday
should be noticeably cooler with the passage of the front.


As of 145 PM Monday: An upper level trough will persist over the
eastern part of our nation through the weekend and into early next
week. Some differential heating from terrain features in the
mountains along with low level easterly to southeasterly flow
against the mountains will assist in producing a bit of convection
each afternoon. Of course, upslope flow will be better according to
the orientation of the ridge lines with wind flow. As the center of
the high slowly shifts from the Great Lakes to New England, the low
level wind flow will shift from easterly to more SE. CAPE values
will be low with under 400 for the mountains each day. The next
significant shortwave will cross the Great Lakes early next week
with moisture building ahead of it.  There may also be a tropical
contribution to this moist flow as models show a tropical system
crossing the western Gulf and getting caught up in the overall flow.
This development will make some POP necessary at the end of this

Temperatures will be around 5 degrees below normal over the weekend
then at the very least overnight lows will be a few degrees below
but with any additional moisture could be close to normal.


KCLT and Elsewhere: VFR through the period at all sites aside for
at KAVL where mtn valley fog is expected near daybreak on Tuesday.
Otherwise, deep ridging prevails across the region which should keep
convection at bay at most terminals, with sct/num shra expected over
the mtns this afternoon.  Therefore, did include vcsh at KAVL for
now, however wouldn`t be suprised if a shra/tsra amd is needed at
some point this afternoon.  All other sites are dry with llv cu and
current light/vrb flow veering southerly almost immediately.  As
stated, added fm group for IFR fog at KAVL tomorrow morning, with
all other sites remaining VFR through the period.

Outlook: Chances for diurnal convection and morning mtn valley
fog/low stratus gradually increase during through midweek, with the
best chances expected Wednesday, as a cold front pushes into the
area. Chances for restrictions and diurnal convection may diminish
again during late week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High  97%     High  94%
KAVL       High 100%     High  97%     Med   78%     High  90%
KHKY       High 100%     High 100%     High  97%     High  94%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  94%     High  91%

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:




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