Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 281842
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
242 PM EDT Fri Apr 28 2017

.SYNOPSIS...
A Bermuda high will bring almost summer like weather to the western
Carolinas and northeast Georgia for most of the weekend, until a
strong cold front approaches from the west Sunday night. The cold
front will move across our region on Monday. After the front passes,
weak high pressure will move across the southeast for Tuesday and
Wednesday. However, the atmosphere will reload with another slow
moving system that may bring wet weather for late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 225 PM EDT: skies have scattered out over most of the CWFA
during the past few hours with mostly clear skies over the higher
terrain. Chances for convection to develop over the next several
hours are still looking pretty slim with the mid-lvl cap in place.
Temps are on track to top out well above normal this afternoon
with even warmer values expected tomorrow that will approach 90
degrees over the lower elevations. Otherwise, upper-lvl ridging
will continue to build over the region thru the near-term period.
At the sfc, sub-tropical high pressure will remain in place to our
east with warm southerly low-lvl flow persisting thru the period.
Chances for diurnally driven convection look slightly better tomorrow
afternoon/evening, especially over the higher terrain as the mid-lvl
cap looks weaker over that region and ample instability should exist.
Elsewhere, I only included a slight chance POP for TSRA on Saturday.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
As of 2pm Friday:  Main short-term event will be passage of major
frontal system with precipitation/thunder on Monday.  With 500mb
ridge off the southeast US Saturday evening, little more than a few
upslope showers in the Southern Appalachians are expected with the
southerly low-level anticyclonic flow Sunday through Monday
morning.  SSW flow will maintain low to mid-60s dewpoints and give
warm lows 10 to 15 degrees above normal Sunday and Monday with highs
Sunday and Monday being held-back by extensive cloud cover.
Precip. chances advance with approach of frontal system. Current
timing places surface front over the mountains Monday morning,
exiting the area to the southeast by Monday evening. Dewpoints
drop 10 degrees behind the front, and the threat of any
precip./thunder will end with its passage, with Tuesday morning
dry and clear and returning to seasonally normal low
temperatures.

Continuous SSW surface flow ahead of front will maintain CAPE
through FROPA on Monday.  CAPE on Sunday is forecast to 2000 j/kg
with weak capping.  However, forcing is nonexistent and deep layer
shear is weak.  While any terrain-related showers on Sunday would be
thunderstorms, extent and severity is expected to be limited.  On
Monday afternoon, significant dynamical factors with surface front
and upper vorticity advection will lead to wide-spread thunder.
However, extensive cloud-cover will hold back temperatures, which
will reduce the afternoon CAPE to 500 j/kg.  However much better
effective shear and more general coverage would make severe storms
more likely on Sunday.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
As of 200 PM EDT Friday: The medium range fcst period kicks off
Tuesday morning amidst longwave H5 troffing atop the east/central
CONUS, while at the surface a cold front moves off the east coast as
weak high pressure slides in from the west across the deep south.
A brief period of cooler/drier air advection is plausible behind
the front on Tuesday before the aforementioned surface ridge
shifts eastward over the western Atlantic, and another upper wave
deepens over the southern Plains leading to surface cyclogenesis
atop the lower/mid MS River Valley for Wednesday.  From that point
forward the fcst will get increasingly wet across the the southeast
states, to include northeast Georgia and the western Carolinas
as upglide/upslope showers will move in Wednesday night into
Thursday morning, while a surface wave and associated warm front
move through the region on Thursday leading to increased chances
for deeper convection and thus tsra.  Meanwhile, the upper pattern
will become increasingly amplified leading to development of a
closed and slow moving upper low atop the Arklatex region on Friday.
With that, llv GOM/ATL moisture fluxes will increase into Saturday
across the southeast leading to higher chances for shra/tsra,
possibly heavy rainfall and flooding as well given the pattern.
Temperatures through the medium range will be a bit variable,
however should hover in the vicinity of normal, leaning mostly
above normal.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: expect predominately VFR conditions for the
18z taf period with some brief MVFR visby and IFR cigs at KCLT from
roughly 9 to 12z and similar restrictions at the other sites. Confidence
is not very high wrt the IFR cigs as cloud cover may remain sct during
that period and a ceiling does not actually develop. Otherwise, the
synoptic pattern will change little over the next 24 hrs with warm,
sly low-lvl flow persisting over the region and wind speeds picking
up this afternoon and tomorrow afternoon as we mix out. TSRA development
remains unlikely today/tonight as we should remain capped, however
increased daytime heating tomorrow could erode the cap and allow sct
convection to develop. This scenario will be most likely over the
higher terrain tomorrow afternoon.

Outlook: Areas of fog will be possible each morning as the near
surface layer remains moist through the weekend. Diurnally-based
showers and thunderstorms will be possible on Sunday, with more
organized thunderstorms possible on Monday.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High  95%     High 100%     Med   70%     Med   77%
KGSP       High  95%     High 100%     Med   74%     Med   78%
KAVL       High 100%     High 100%     High  83%     High  93%
KHKY       High  92%     High 100%     High  81%     Med   75%
KGMU       High  92%     High  97%     High  89%     High  81%
KAND       High  91%     High 100%     High  94%     High  85%

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...JPT
SHORT TERM...WJM
LONG TERM...CDG
AVIATION...JPT



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