Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201945
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
245 PM EST Mon Feb 20 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 TUESDAY/...
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 /TUESDAY NIGHT 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 /20Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: High pressure will slide east, allowing
surface and low-level flow to turn out of the SE thru the
period. This flow will tap into some Atlantic moisture, but guidance
is mixed on how much low cloud development there will be late
tonight thru midday Tuesday. I used a compromise for the grids,
which has plenty of MVFR and spotty IFR cigs develping around
daybreak, mainly near the Blue Ridge escarpment. At KCLT...given
it`s further away from the mountains, I only have SCT IFR clouds
Tuesday morning for now. Winds will be light and rather variable
this afternoon and evening, but will generally range from ENE to
ESE.

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 in
mainly stratus each day thru at least Thursday.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High 100%     High  92%     Med   79%
KGSP       High 100%     High 100%     High 100%     High  80%
KAVL       High 100%     High 100%     High 100%     High  94%
KHKY       High 100%     High 100%     High  90%     Med   72%
KGMU       High 100%     High 100%     High 100%     High  82%
KAND       High 100%     High 100%     High 100%     Med   69%

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...Wimberley
NEAR TERM...ARK
SHORT TERM...RWH
LONG TERM...Wimberley
AVIATION...ARK


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