Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 230600

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
100 AM EST Thu Feb 23 2017

Brief drying develops today into early Friday before a significant
cold front brings chances for rain and thunderstorms Friday night
and Saturday. Overall, daytime temperatures will remain well above
normal through Saturday, with a return to normal for Sunday. Above
normal temperatures and chances for rain return for early next week.


100 AM EST Update...Keeping an eye on the dense fg potential
overnight. The suspect areas look to be the NC mtn valleys...fthills
and piedmont per sfc layered cdp/s and recent obs. Tdd/s are running
a little high across the Upstate...however this is the area that
received better precip yesterday.

0230 UTC Update: Minor changes were made to overnight temperatures
based on the latest model guidance.

As of 230 PM EST...An upper low will continue to drift SEWD over FL
tonight thru thursday, while an upper ridge builds back in across
the Southeast states. At 850 mb, the circulation around the upper
low will keep a persistent SELY Atlantic fetch into the CWFA. This
will keep plenty of low clouds and fog for the overnight thru
Thursday morning. Forcing remains weak, so only spotty light showers
and patchy sprinkles/drizzle is expected, and mainly favoring the
SELY upslope areas of the Blue Ridge. That`s where PoPs will be
highest (in the chance range, slight chance or less elsewhere).
Temps will only cool slightly under the clouds, into the upper 40s
to mid-50s.

During the day on Thursday, expect the low clouds and fog to
eventually lift and scatter out, revealing some sunshine, especially
in the southern Piedmont. Lingering surface high pressure will nose
in from the east, but temps should be able to warm into the 70s
across the entire Piedmont with nothing to lock in any remaining
cold pool.


As of 240 PM EST Wednesday: Short wave ridging builds over the area
Friday before an upper low developing over the Northern Plains moves
east across the Great Lakes on Saturday dragging a trailing trough
across our area. Southerly low level flow remains over our area
Friday as high pressure moves east and a strengthening cold front
moves into the MS valley. There will be enough low level moisture to
combine with the flow for some isolated showers along the Blue Ridge
Thursday night/Friday morning and scattered showers and isolated
thunderstorms on Friday afternoon. Lows will be 15 to 20 degrees
above normal with highs around 20 degrees above normal but still a
couple of degrees below record levels.

Winds pick up and moisture increases Friday night as the cold front
to our west moves into the mountains toward daybreak. However, deep
moisture is shunted off to the north. The best forcing is also to
our north where the best short wave energy moves through the trough.
Despite the guidance showing some elevated instability ahead of the
front, the NAM and GFS forecast soundings show quite a cap in place
for all but maybe the NC Mountains and I-40 corridor. The best
SBCAPE develops during the afternoon east of our area as the front
quickly moves across the area. There will be quite a bit of bulk
shear and helicity ahead of the front. However, the best instability
and shear do not overlap over our CWFA. Therefore, the chance of any
severe storms is very low, but we will need to keep an eye on this
system as it approaches. There will be some NW flow snow showers
along the TN border in the lingering moisture and developing NW flow
behind the departing front. However, any accums look to be below
advisory level for now. Finally, winds will increase and become
quite gusty across the high elevations ahead of the front Friday
night then all areas on Saturday behind the front. Winds linger
across the high elevations Saturday night. Lows Friday night around
20 degrees above normal fall to near normal Saturday night. Highs
Saturday will be around 10 degrees above normal across the
mountains, and could be earlier in the day than normal, and 15 to 20
degrees above normal elsewhere.


As of 2 PM EST Wednesday...starting to wonder if winter is really
over. The upper pattern looks like it should remain progressive
through the medium range with all the colder air kept well to our
north. In the wake of the Saturday system, expect Sunday will be the
only seasonal day in the first half of next week. We should be under
a flat ridge that supports high pressure at the surface, which
should keep temps merely five degrees above normal. After the
surface high moves off the coast Sunday night, our weather should
get more active through the rest of the period. A short wave moving
over the Srn Plains Sunday night will organize surface low pressure
that moves up the OH valley on Monday. Model guidance is not in very
good agreement as to how organized or deep the low will be, but
there is some agreement that a surface front will lay down across
the area Monday and Monday night. Precip prob slowly ramps up into
the chance range over the mtns and a slight chance east of the mtns.
The models suggest a lull in the action Tuesday morning, so will try
to indicate a break in the low-end precip chance at that time. There
is also some agreement that the old boundary will reactivate Tuesday
night as another low organizes over the Plains. Altho this low will
track over the Midwest/Gt Lakes, it should push a cold front toward
the region on Wednesday. That should bring a chance of precip across
the whole fcst area. Will hold back with including any likely precip
prob due to lack of confidence out on day 7. Temps will gradually
rise through mid-week, getting back up into the well above normal
range for Wednesday.


At KCLT...Expect lowering of cigs overnight as back end of cloud
shield works east. Vsby will also lower as hires cpd/s show max
saturation in the sfc layer around daybreak. A drop to IFR conds by
10z and possible LiFR vsby by 12z. A lifting and scattering out will
occur quickly aft 15z with drier air mixing in underneath a building
mlvl ridge allowing for good sfc heating.

Elsewhere: KHKY will be the trouble spot wrt to IFR/LIFR conds thru
daybreak. Previous rainfall and calm conds under a sfc ridge will
enable a highly moist sfc layer to persist thru mid morning. KAVL
will also be under the gun for IFR vsby/cigs a few hrs before
daybreak. Across the Upstate...VFR dropping to MFVR conds with
perhaps IFR vsby...esp at KGSP/KGMU where tdd/s are running lower
and cpd/s drop the most. A quick return to VFR conds will occur arnd
14z with relatively drier air mixing in and sfc heating commencing.

Outlook: Moist southerly to easterly low-level flow will persist
across the area until a cold front pushes thru on Saturday. This
will keep high chances of morning stratus and possibly fog each day
thru Saturday morning. Drier conditions set up on Sunday.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High  90%     Med   76%     High 100%     High 100%
KGSP       High  80%     High  92%     High 100%     High 100%
KAVL       Med   66%     Med   79%     High 100%     High  97%
KHKY       Med   66%     Med   77%     High  99%     High  97%
KGMU       Med   79%     Med   77%     High 100%     High 100%
KAND       Med   79%     Med   77%     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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