Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220729
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
329 AM EDT Thu Sep 22 2016

.SYNOPSIS...
A weak area of low pressure lingering along the coast of the
Carolinas today will drift east on Friday. A broad upper ridge and
surface high pressure will build over the region during the weekend
as temperatures rise well above normal again.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 250 AM Thu: Still dealing with the effects of easterly flow
around sfc/upper low over the Carolina coast. Pockets of light
showers continue to move WSW from the Triangle to the Piedmont
Triad, and while they thin out as they move into the drier air
over our CWFA, they are beginning to make inroads. HRRR expects
they will reach the Hwy 321 corridor before fizzling out around
daybreak. A chance-range PoP is retained over the ern zones thru
the morning. Thicker and lower cloud deck will also move in this
morning, and guidance consensus indicates that will hang around
well into the afternoon. Max temps are impacted, being just a
couple degrees above normal across most of the area--the upper
Savannah valley is expected to remain sunnier and still reach the
upper 80s in spots.

While some pockets of light stratiform rain will move through the
Piedmont at times today, convection is expected to be a bit more
widespread than yesterday, on account of slightly improved lapse
rates. Meso models depict isolated convection over the Blue Ridge
and parts of the lower Piedmont, similar to what verified yesterday,
though with a little more QPF. Thunder is still too unlikely to
mention. The low wobbles slightly northeast along the coast tonight,
keeping the low level pattern pretty much the same. High pressure
strengthens a bit over the Mid-Atlantic and down the southern Apps;
this holds back the advance of clouds and precip, chances of which
taper off overnight. Min temps across the area will be around 10
degrees above normal.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
As of 230 AM EDT Thursday...still expecting the weekend to be
relatively benign weather-wise...although quite warm. The model
guidance continues to show the old upper low opening up and filling
along the Carolina coast on Friday, although at least some remnant
of the upper system appears to be left to drift westward along the
Gulf Coast, underneath the upper ridge, on Saturday. Whether or not
this feature is the actual upper low should be immaterial, as the
western Carolinas come under the influence of the amplifying upper
ridge from Friday thru Saturday. The plume of wrap-around moisture
might be sufficient to maintain a few showers over the eastern zones
early in the day on Friday, but this will get pushed off to the east
in the afternoon. Some instability over the SW mountains of NC might
allow for a few showers over the higher terrain in the afternoon.
Otherwise, expect most locations to remain dry with high temps
climbing five degrees or so warmer than Thursday, back to almost
Summer-like heat. That trend will continue into Saturday with only a
few ridge-top showers able to break through a strong cap. High temps
should be well above normal...and very much like summer. Uncertainty
begins to creep in from the east on Sunday with some indication that
surface high pressure moving across the Gt Lakes will impose an
easterly flow that will bring some Atlantic moisture over the
region. Fcst soundings from the GFS show the low level moisture
allowing for more sfc-based buoyancy...enough to warrant a chance of
precip over the mtns and foothills by afternoon. This seems
reasonable enough to keep a small chance in the fcst. Temps may be
held in check by increased cloud cover Sunday afternoon, at least
over the NC part of the fcst area.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
As of 315 AM Thursday...you would find it difficult to remember a
time in your recent memory when the operational runs of the medium
range models had less run-to-run continuity and less agreement with
the upper pattern as you see by the middle of next week. Whether the
pattern will remain progressive or amplified or become blocked is
difficult to determine right now, leading to much greater
uncertainty than usual for this time of year. There is at least some
agreement that at some point a frontal boundary will get strung out
close to the fcst area in the middle or late part of the week, so
there is hope of getting some much-needed rain. Details are very
sketchy though. At this point, prefer to not make any changes in the
medium range and will look toward hopefully seeing some consistency
and/or trend in the next model cycle.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
At KCLT: Low pressure over the eastern Carolinas will sustain
northeasterly flow over the field thru the period. MVFR to IFR
stratus will expand westward thru central NC early this AM, along
with bands of light showers. MOS guidance generally progs KCLT
seeing IFR by daybreak, whereas raw models (including hi-res runs)
generally favor low MVFR. The best performing guidance in this
pattern has been raw, but with IFR under 100 SM away, I can`t deny
the possibility. Hence TEMPO IFR for now; will refine this at 09z
per latest guid/obs. The moist layer is deep enough that daytime
improvement will be much slower than usual. Lapse rates are a tad
more favorable than those Wed, so SCT SHRA are expected this aftn.

Elsewhere: MVFR cigs are expected to advect over KHKY/KGSP/KGMU
around dawn or a little later. KHKY has a small chance at IFR,
with same reasoning as outlined for KCLT above. Some sprinkles
are possible in the morning as bands of better forcing round the
low. Also, once cigs finally lift and/or scatter a bit, there
should be more coverage of aftn SHRA than the past couple days,
though still too isolated to mention in TAFs. Winds mainly NE thru
the period, with no restrictions anticipated tonight prior to 06z.

Outlook: Meandering low pressure along the Carolina coast will
persist thru Friday. This will allow isolated to scattered diurnal
convection to continue especially east of I-77, and periodic
chances for restrictive cigs. Meanwhile, a new cold front will be
approaching from the northeast Sunday, but with sparse precipitation
expected at this point.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  91%     High  97%     High  97%     High 100%
KGSP       High  99%     High  88%     High 100%     High 100%
KAVL       High  84%     High  94%     High 100%     High 100%
KHKY       High  98%     High  89%     High 100%     High 100%
KGMU       High 100%     High  88%     High 100%     High 100%
KAND       High 100%     High  90%     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...PM
NEAR TERM...Wimberley
SHORT TERM...PM
LONG TERM...PM
AVIATION...Wimberley



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