Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 190725

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
325 AM EDT FRI AUG 19 2016

Warm and humid conditions will continue into this weekend within
lingering subtropical high pressure. A cold front will push in from
the northwest late Sunday bringing cooler and drier air to the
region for the first half of next week.


As of 315 AM EDT...A flat split upper-level flow will exist across
the eastern CONUS today through tonight. The "southern stream" is a
weak relative maximum of flow extending from the TX Panhandle to the
Mid-Atlantic, generally 40-50 kts at 300 MB. However, channeled
vorticity and some upper divergence will persist within the flow
atop the CWFA this afternoon and evening. Very moist atmosphere in
place with PWATS over 2" should combine with the subtle forcing to
produce another round of scattered convection with daytime heating.
With that said, the moist mid-levels and perhaps more clouds
limiting insolation will keep instability modest. DCAPE will also be
low, so overall severe threat should be low today. Locally heavy
rainfall will probably be the greater threat, but storms should
generally move enough to prevent flash flooding. Highs will be about
2-4 degrees above normal, with low 90s across most of the Piedmont.

Tonight...Convection should gradually wane this evening, leaving
another muggy night under plenty of mid and high cloudiness and some
patchy fog, especially in the mountain valleys. Lows will continue
to be a few degrees above normal.


As of 3:15 AM EDT Friday: The short term part of the forecast on
Saturday features a rather zonal looking H5 flow during the day,
with both the GFS and NAM showing ripples of energy riding along
this H5 wave train. Meanwhile the surface pattern has some flavor of
an old front or boundary in the area which will also help focus
thunderstorms. PW`s by both the NAM and GFS rise to near or over 2.0
inches. As a result we would expect another round or two of storms,
with likely POPS in the mountains and solid chances elsewhere.

The H5 trough digging into the middle part of the country Saturday
night will begin to back the mean flow. Isentropic upglide on
Saturday night, combined with deep moisture, will signal
precipitation hanging on a bit longer than the usual diurnal cycle.

As the deep upper trough swings through the Ohio/Tennessee Valleys
and the Great Lakes, a fairly decent cold front will sweep across
our forecast area Sunday and Sunday evening. We would expect more
thunderstorms, perhaps somewhat organized, considering a slight
uptick in shear, and instability still in place. We will have to
keep an eye out during this time particularly.

Perhaps less of a diurnal temperature cycle as well during this
period with high temperatures tempered by clouds and precipitation
both during the day and at night.


As of 3:15 AM Friday: It appears high pressure, both at the surface
and aloft, will settle across the southeast early in the work week.
Longer range models, at least at the onset, suggest cooler
temperatures and dry conditions.

Later in the week, high pressure slipping off the eastern seaboard,
may tend to drive some moisture into the Upper Savannah Valley, and
parts of the western Carolinas - from the Atlantic and eastern Gulf
of Mexico.

We start to notice POPS edging back toward climatology, as a result
we will run some lower POPS probably on Thursday in parts of our
western forecast area.

Meanwhile, we are in the ballpark with current guide temperatures,
which seem to be clustered around each other.


At KCLT...Despite plenty of upper-level debris cloudiness from
earlier convection, there is some patchy stratus developing due to
the wet ground across the Piedmont. The flow is light out of the NW
and I expect the low CIGS to mainly be around over the next couple
hours. Some of the guidance hints on the stratus still expanding
across much of the Upstate and Midlands, but staying south of CLT
during the pre-dawn hours. Later today, another round of scattered
SHRA and TSRA is expected to develop across the area. So a PROB30
for TSRA will be retained from 19-24z. Winds will be light, but
favor the NW through daybreak, then switch out of the SW, increasing
slightly during the afternoon.

Elsewhere: An area of SHRA continue to linger around KHKY, while the
rest of the area is quiet. With numerous SHRA earlier this evening
across the lower Piedmont, some guidance is starting to hint at some
low stratus development (with some already developing around KCLT).
However, with NWLY low-level flow and plenty of upper-level debris
cloudiness, I think it should remain patchy and whatever does develop
generally SE of the Upstate sites. KHKY may be in and out of stratus
and fog due to the recent late evening rain. KAVL is tricky, as
there were showers around earlier that wet the ground and flow is
light. However, the debris cloudiness and still 4-degree dewpoint
depressions should limit valley fog/stratus. I kept the 4-hour tempo
for IFR there. Otherwise, another round of scattered SHRA and TSRA
warrants PROB30 at all sites for this afternoon.

Outlook: Scattered to numerous showers and thunderstorms are
expected across the region again on Saturday. A cold front will push
in from the northwest on Sunday, enhancing the chance for
convection. Much drier air will filter in behind the front Monday,
resulting in fair weather through midweek.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       Med   79%     High  93%     High  98%     High  86%
KHKY       High  85%     High 100%     High 100%     High 100%
KGMU       High  99%     High 100%     High 100%     High 100%
KAND       High  90%     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:




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