Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 282247

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

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.


As of 6 PM EDT: Overall, the Cu field will continue to steadily
diminish this evening although clouds could linger near the upslope
areas thanks to the ongoing llvl waa flow. Weak vort rippling
northward from the gulf coast may aid in spreading some cirrus our
way as well.  Within the weak and very moist blyr flow areas of fog
and stratus is expected to redevelop overnight. Upper-lvl ridging
will continue to build/linger atop the region thru Saturday. At the
sfc, sub-tropical high pressure will remain in place to our east
with warm southerly low-lvl flow persisting. 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.


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.


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.


At KCLT and elsewhere: VFR conditions will continue this evening
with the chances for developing flight restrictions, in the form of
low stratus and fog, steadily increasing overnight.  At this point,
a period of MVFR vsby and/or IFR stratus will be fcst for KCLT
during the pre-dawn hours before quickly mixing out before 14z. As
Saturday wears on, southerly winds will increase to abt 10 kts as Cu
field steadily rises and expands. Best chances for afternoon
thunderstorms will be over the mountains.

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...

            22-04Z        04-10Z        10-16Z        16-18Z
KCLT       High 100%     High 100%     Low   55%     High 100%
KGSP       High 100%     High 100%     Med   63%     High 100%
KAVL       High 100%     High 100%     Med   61%     High 100%
KHKY       High 100%     High 100%     Low   59%     Med   78%
KGMU       High 100%     High  91%     High  80%     High 100%
KAND       High 100%     High 100%     High  87%     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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