Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 250227

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1027 PM EDT TUE MAY 24 2016

High pressure will prevail over the Southeast most of this week. A
moist southerly flow will develop in mid week, which will
lead to warmer temperatures and mainly afternoon chances of showers
and thunderstorms each day through Friday.


As of 1030 PM EDT: Minor adjustments have been made to lower
piedmont/foothill minimum temperatures a degree or so overnight
given the good radiative cooling thus far this evening. However,
still anticipate that mid level moisture will slowly increase from
the west with an approaching upper shortwave - with additional
scattered stratocumulus possibly fanning out in narrow moisture
below a weak 800 mb inversion. The increasing mountain clouds should
keep most valley fog at bay but with the best chance of fog in the
southwest mountain valleys.

Weak southerly flow around the periphery of the western Atlantic
surface high will continue to bring moisture into the area through
Wednesday. This will help push max temps a couple of degrees warmer
on Wednesday afternoon. Enough deep-layer moisture and weak lift
will also arise over the mountains for slight to low chances of
thunder Wednesday afternoon. Given the increase in afternoon
cumulus, SBCAPE should be limited with generally less than 500 J/kg
with slightly higher amounts localized over the peaks. The main
threat would be with cloud-to-ground lightning.


As of 230 PM Tuesday:  The short term fcst period initializes
Wednesday evening amidst a broad, yet slowly weakening upper ridge
centered over the southeast states, while a large H5 trof digs over
the desert southwest.  At the surface, high pressure over the
western Atlantic will continue to promote weak southerly waa across
the southern Appalachians as cyclogenesis gets underway ahead of the
a fore mentioned H5 trof atop western KS/OK/TX.  Closer to home, a
weak shortwave impulse riding through the apex of the upper ridge
combined with ample llv destabilization will have resulted in
iso/sct shra and tsra over the NC high terrain by 00z Wednesday.
With that, profiles are indicative of pulse type convection amidst
weak flow throughout the column and ever improving deep layer
moisture.  Pwats aren`t all that impressive, generally 1.25-1.5
inches at best, however given the weak flow and modestly elevated
lcls, think the primary convective concern will be wet microbursts
as well as isolated flash flooding amidst any slow moving
heavier/deeper convection.

Moving along through the period, not much change synoptically on
Thursday and Friday as the subtropical ridge persists over the
southeast CONUS, with continued southerly waa at the surface.
Precipitation chances remain elevated over the high terrain where
any inhibition will be weakest each day allowing for more widespread
initiation with heating.  As for the remainder of northeast GA and
the western Carolinas, precipitation chances will be lower through
the period relative to the mtns given proximity to the ridge center,
however said chances do increase with time as guidance favors
generally unstable and uncapped profiles both Thursday/Friday with
improving pwats and weak flow aloft. All said, the threat for pulse
convection induced flash flooding will increase over the NC mtns
given degrading antecedent conditions each day.  Antecedent
conditions over the piedmont regions will also be degraded with
time, however relatively less than that of the mtns, yet still
presenting a non zero threat for hydro issues.  Lastly, guidance
continues to indicate, although with some discontinuity regarding
the details, that a weak tropical low is to form/strengthen over the
western Atlantic and eventually approach the southeast coast on
Friday evening.  Although any specific impacts from this feature are
beyond the scope of this fcst time frame, it should be noted that
flow over the southeast does look to back as the system approaches.
This could yield improving upslope flow conditions along the blue
ridge for Friday.


As of 2 PM Tuesday:  An upper ridge east of the Mississippi and
broad upper trough to the west on all models at 00z Saturday. The
ridge broadens over the weekend and into the first half of next week
as tropical moisture moves toward the Carolinas from the Bahamas.
Diurnal convection is expected each PM but so much depends on where
this tropical moisture ends up.  The GFS is still bringing the weak
low more to the west than the ECMWF. The GFS gives the western
Carolinas and NE GA tropical rains late Sunday into the first half
of the week while the ECMWF has us mostly dry. National guidance
remains of opinion that organized tropical development has low
chance.  7 day rain total guidance are now showing upslope
enhancement rainfall of at least 1.5 along eastern Escarpment. GFS
now takes the weak tropical low up I-26 from Sunday evening to the
NC Mtns on Tuesday.  Whenever there is a named TC, the first one
will be named ALEX and secondly BONNIE. That may take a while though.

Low level wind flow will depend greatly on the track of the
counterclockwise circulation of low pressure.  The ECMWF has mostly
light and variable on Saturday then east and NE Sunday into Tuesday
with a projected low center crossing the NC coast. ECMWF and GFS has
less than 500 CAPE Saturday PM.  Instability generally 1000 to 1500
CAPE are forecast by the models each PM.

Max temps well into the 80s on Saturday, Gradually cooling off to
70s Mtns and 80 to 84 foothills and piedmont Mon and Tuesday due to
the increased clouds and tropical saturation. MINs in the 60s.


At KCLT and elsewhere: Daytime cumulus has dissipated, but mid level
moisture is increasing slightly over the mountains ahead of a weak
approaching upper wave. Most locations may also see at least FEW to
SCT high based stratocumulus overnight as a narrow moisture zone is
trapped beneath a weak inversion layer. Some brief fog in the
southwest mountain valleys is possible toward sunrise, but mid and
high clouds should keep the fog from becoming dense. Cumulus
production and mid level moisture will increase through Wed from the
west. Isold to scattered mountain ridge top showers are expected
through late Wed, but with the confidence too low for any mention at
KAVL or the other airfields. Expect generally light SW winds through
the period, with max flow 5 to 10 kt during mixing on Wed afternoon.

Outlook: Mainly VFR conditions will prevail through the period, but
patchy morning fog chances continue at KAVL. Scattered afternoon
SHRA/TSRA coverage will increase Thursday through Friday - with more
uncertainty on Sat.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
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 schedule 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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