Area Forecast Discussion
Issued by NWS Greer, SC

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574
FXUS62 KGSP 210537
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1237 AM EST Tue Feb 21 2017

.SYNOPSIS...
Warm and dry conditions will continue through Tuesday afternoon. A
frontal zone pushing across the area late Tuesday and Wednesday
will bring a chance for some modest rainfall. This will be followed
by brief drying, before another frontal system at the end of the
week brings additional rain and thunder chances.

&&

.NEAR TERM /THROUGH TODAY/...
1230 AM EDT Update...no major changes needed to the grids. Upper
level Ci continues to stream across the fcst area...however some
areas are running below the projected diurnal curve. MinT will be
adj slightly.

As of 1025 PM EST Monday:  Light/calm winds beneath sct/bkn high
cirrus highlights the weather across Northeast GA and the Western
Carolinas this evening.  Latest IRSat imagery favors banding of
cirrus streaming aloft from upstream convection in association
with the highly amplified MS River Valley trough.  Meanwhile, high
pressure anchored over the northeast continues to gradually sag
southward in the Lee of the Southern Appalachians, with a back door
front looking to intrude into the Carolinas overnight.  With that,
still expecting saturation of llv moisture trapped beneath a
strong mlvl inversion which will lead to increasing low stratus
toward dawn.  As a result of the aforementioned cirrus/cirrostratus
and the potential low stratus, opted to blend in latest consshort
temps through the night which effectively raised min temps around
a degree for most locales.  Otherwise, tweaked t/td/sky and wind
trends to reflect latest obs/sat and left the remainder of the
immediate near term as it was for this update.  Lastly, latest
NAM indicates hints of a slower precip onset tomorrow afternoon,
however given the already low chances currently in the fcst,
opted for no changes at this time.

As of 200 PM EST...A highly amplified upper ridge will shift slowly
east across the CWFA tonight, while an upstream trough will split
and close off a low over eastern TX. At the surface, high pressure
sets up along the East coast, keeping a light easterly flow across
the Carolinas. As the high pressure system slides east, low-level
flow will turn out of the SE, and advect some Atlantic moisture into
the southern Blue Ridge escarpment by daybreak Tuesday. This should
result in some stratus developing across the SELY upslope areas and
adjacent foothills. This in combination with thickening cirrus will
result in a mostly cloudy night for the area. Temps will be held
well above normal, mainly in the 40s to around 50 degrees for lows.

On Tuesday, the surface high will remain along the coast, while
moisture gradually deepens within the southerly flow aloft. Under
mostly cloudy skies, temps will be not as warm as last couple days,
but still well above normal. Highs mainly in the 60s to lower 70s
in the southern tier. The moist layer in the profiles in the SW
mountains will get deep enough for slight CHC to low-end CHC pops
ramping up by the end of the day. But otherwise, it should be dry.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
As of 230 PM EST Monday: An upper low over the MS/LA border slowly
slides SE to near Tampa Bay on Wednesday as weak northern stream
short wave energy passes by to our north. The low crosses FL on
Thursday as additional weak short wave energy passes by to our
north. The associated surface low pressure system takes a similar
track as the upper system. This results in SE to S H85 flow into our
area with deep moisture moving in. PoPs will increase into the
likely range across the mountains with good chance elsewhere Tuesday
night then slowly diminish through the day Tuesday as the low moves
south and the low level flow weakens. There is some decent upper
divergence developing over the area as well with an upper jet
couplet moving through. QPF should remain in the light to moderate
range with the relatively quick movement and moderate flow. Highs
Wednesday will be much cooler with the precip, clouds and weak high
pressure nosing in from the east in weak cold air damming or cool
pooling pattern. However, they will still be 5 to 10 degrees above
normal. Lows will be around 15 degrees above normal.

The low level flow continues to weaken Wednesday night and Thursday
as the upper and surface low remain to our south over FL. However,
there will be enough lingering moisture to interact with the
southerly flow for slight chance PoP across the mountains Wednesday
night and chance PoP on Thursday. Slight chc values expected across
the rest of the area Thursday. There may even be some weak
instability developing for isolated TSRA to develop during the
afternoon as the surface ridge weakens. Highs and lows Thursday
rebound to 15 to 20 degrees above normal with fewer clouds and more
showery precip developing.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 225 PM Monday, the upper flow pattern over the eastern Conus
will amplify briefly at week`s end, as a major short wave trough
ejects from the southern Great Plains. Ahead of this feature and
attendant frontal zone, SW flow will support plenty of warmth and
improving low level moisture profiles on Friday, with some weak
surface-based instability depicted in global model forecast
soundings by Fri afternoon. Nevertheless, the soundings appear
generally hostile to convection, mainly owing to an inversion
between H7 and H8. With guidance pointing strongly to the idea that
the front will not cross our area until Friday night/early Sat, the
inherited pop forecast for Fri afternoon appears to be much too
generous, and pops have been lowered to 20 percent across much of
the forecast area (even that may prove to be too high).

As far as precip chances associated with the front itself, a
consensus of global model guidance would suggest the deep layer
forcing associated with the short wave will lift west and north of
the southern Appalachians, albeit a bit closer to home than what was
depicted in yesterday`s guidance. That being the case, and with
little instability and only a weak frontal circulation, both the
ECMWF and GFS indicate a substantially weakening band of frontal
precip moving into the forecast area Fri night. Pops will range from
40 percent across southern areas to 50-60 percent across the
remainder of the area. If anything, chances for strong to severe
convection appear lower than in yesterday`s guidance (when they
didn`t look that great to begin with).

Condition dry out substantially and cool a bit by the end of the
weekend, with temps expected to be about 10 degrees above climo next
Sunday and Monday. Precip chances may ramp up again by the end of
the period, as a fast moving system approaches the East Coast.
However, global model guidance is currently not in good agreement
regarding the timing of precip chances in our area.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: BKN/OVC Ci will persist across all TAF sites
through most of the period. Meanwhile...an increase in llvl moisture
will adv in from the Atl this morning and generate STCU in e/ward
facing mech lift. Expect most sites limited to VFR CIGs...however
the nrn fthills including KHKY will see the best chance for MVFR/IFR
CIGs shortly after or around daybreak. Winds will remain rather
light as a sfc high remains wedged across the area with a low-end
ageo adj potential. Expect -shra to start moving in from the west
associated with a warm front...thus prob 30s will begin aft 00z west
and by 04z at KCLT.

Outlook: An area of low pressure will drift from the Southern Plains
to near FL, keeping a persistent moist southerly flow across the
area thru Wednesday. This will result in periods of restrictions
by way of stratus each day thru at least Thursday.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
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...SBK
NEAR TERM...ARK/CDG/SBK
SHORT TERM...RWH
LONG TERM...Wimberley
AVIATION...SBK



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