Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181843
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
243 PM EDT Mon Jun 18 2018

.SYNOPSIS...
Hot high pressure will build over the region through the middle of
the week. Scattered afternoon and evening thunderstorms are expected
each day, focusing over the mountains. Moisture will increase toward
the end of the week as a weak frontal boundary sags south into the
area.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 235 pm: Seeing some enhanced cu mainly across the ridgetops
as of mid-afternoon...and a few strong storms developing over the
higher terrain. No real changes in thought for the rest of the
afternoon. Still feel that in spite of relatively poor mid-level
lapse rates and the suppressive affects of the upper ridge, we
will still get one or two strong/severe thunderstorms. Steering
flow within the axis of the upper ridge will be extremely weak,
in fact close to zero according to mean LCL-to-EL winds from
forecast soundings. Individual cells will therefore make little
headway into the valleys or the foothills.

Over the next 24 hours...very little change is expected. The upper
anticyclone center will drift a bit to the south and we should see
the start of the breakdown of the ridge, but with no real air mass
change the weather should be persistent. Expect showers/storms to
weaken this evening and dissipate before midnight or so. Valley
fog will develop across the NC mountains once again early Tuesday
morning. For Tuesday afternoon, once again there appears to be no
meaningful mid/upper support. Fcst soundings remain uncapped, but
lapse rates should remain relatively poor and the CAPE profile
is tall and skinny. As we start to feel the weakening ridge,
the flow should start to increase from the west later in the day,
so there is a better shot for storms to develop an easterly drift,
which justifies keeping a slight chance of precip across the area
east of the Blue Ridge. Highs will be well into the 90s again, but
think dewpt stands to mix out just enough once again to keep Heat
Index from getting above about 102F, so no Heat Advy is anticipated.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 145 PM Monday: No sigfnt changes were made to the short range
fcst. The models continue to show good continuity with the ulvl
high breaking down and shifting south over the period. The lowering h5
heights will bring a llvl bndry closer to the FA by Thu while flow
thru the column increases into the 15-20 kt range. This will still
be a very warm pattern and maxes will top out in the mid to upper
90s over the non/mtns. Soundings show sfc td/s will mix-out a bit
each afternoon similar the past few days...or generally lower by a
few degrees. This relative dryness will be enuf to offset a heat adv
concern...however over the srn Upstate and the NC Piedmont the heat
index will come close to criteria or be met in isol locales. Will
thus keep the high heat mention in the HWO. Convection will remain
diurnally driven with no sigfnt triggers and weak mlvl lapse rates.
Expect mtn-top convg to begin the process with more sct tstm
development outside the mtns each afternoon due to the increasing
flow thru the column.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
As of 220 PM EDT Monday: The extended fcst picks up at 00z on Friday
with broad upper trofing moving off the New England Coast and weak
upper ridging over the Southeast. To the west, a closed upper low is
moving east over the Central Plains. As we move into the weekend,
the model guidance has the upper low open up and lift northward and
towards the Great Lakes as upper ridging builds to our east offshore.
By early Sunday, as the upper low lifts northward, it deamplifies
and gets absorbed into the mean northerly flow. For the rest of the
period, we will remain under relatively flat upper ridging as
another upper trof begins to dig down over Eastern Canada and New
England. At the sfc, a rather complex pattern will be in place to
begin the period. High pressure to our north will be situated
between low pressure well to our NE and NW. Thru the day on Friday,
the eastern low will move well offshore while the low to our west
deepens and tracks NE towards the Great Lakes. At the same time, the
high begins to move offshore and we lose its influence on the sfc
pattern. On Sat, the low lifts farther NE and brings a cold front to
our doorstep. The guidance has the front moving thru the fcst area
by early Sunday with SLY flow re-establishing itself across the
region the front`s wake. As for the sensible fcst, both Friday and
Sat will have the best chances for widespread convection with ample
instability and deep moisture over the area. PoPs decrease to around
climatology for Sunday and Monday and we return to a more typical
summer-time pattern. As for temps, Friday and Saturday will see
values near normal if not a few degrees above, and Sunday and Monday
will see values a few degrees warmer than Fri and Sat.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR conditions are expected to persist
through the period at most sites. A few cu should develop thru
the afternoon with cloud bases generally above 050. The chance
of precip at any site looks too low to mention. Cloud cover
should largely dissipate with sunset.  Will not rule out a brief
restriction at KAVL again late tonight or early Tuesday morning,
as the air mass will not change. Tuesday looks very similar to
today, starting out mostly clear with a light northeast wind.

Outlook: Typical summertime pattern will continue through at least
mid-week, with diurnally-driven showers and thunderstorms favoring
the high terrain, and some morning fog possible in the mountain
valleys and over lakes each day. Chances for precip look greater
late in the week as upper ridge begins to break down.

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 100%     High 100%
KAVL       High 100%     High 100%     High  98%     High  97%
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...JPT
NEAR TERM...PM
SHORT TERM...SBK
LONG TERM...JPT
AVIATION...PM


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