Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 281847

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
247 PM EDT Sun May 28 2017

Warm and humid air will remain over our region through at least
Monday, as high pressure settles east of the Florida coast. A cold
front will slowly approach from the northwest, but will struggle to
push through the area in mid week. This front is forecast to
lift north as a warm front late in the week.


The forecast area continues to slowly destabilize this afternoon,
but per the SPC Mesoanalysis, sbCAPE remains at less than 1000, if
not 500 J/kg across much of the area. Meanwhile, cirrus debris
persists over the area, and probably isn`t going to dissipate
anytime soon, so the destabilization process should remain gradual.
This area of cirrus may be associated with a mid-level short wave
trough/MCV depicted in short term guidance. There is a line of
weak/elevated radar returns aligned roughly along the Blue Ridge and
connected to a recently developed shower near the NC/VA border,
which may be a reflection of this wave. Thus, still think we`ll see
at least isolated convection develop over the next couple of hours
near the Blue Ridge and move east late this afternoon/this evening.
However, considering the degree of instability, finding it a tad
difficult to put too much stock in the latest runs of the HRRR,
which evolves Blue Ridge activity into a broken line of pretty
angry-looking convection over the Piedmont this evening.
Nevertheless, the I-77 corridor and SC Piedmont are the most likely
areas to see significant additional destabilization, and with bulk
shear more than adequate for organized convection, a couple of
severe storms capable of producing damaging winds and large hail
still appear possible, mainly this evening. Convection should taper
off by late evening with mainly isolated convection across the
mountains overnight.

Weak baroclinic zone will remain in place across the region through
the end of the period. Guidance indicates large scale height falls
associated with migration of the central Conus trough should
activate this baroclinic zone by Monday afternoon, as indicated by
increasing deep-layer moisture across the Southeast. Scattered to
numerous convection should therefore initiate across our area,
particularly along the Blue Ridge Monday afternoon. Moderate
instability combined with moderate shear will yield another
marginal threat of severe storms producing large hail and damaging
winds again on Monday. Temperatures will remain above normal through
the period.


As of 230 PM EDT Sunday: The short term begins Monday evening with
large upper high over the western Atlantic, with a deep low over
the Great Lakes and southern Ontario. Southwest flow aloft over the
Southeast and Southern Appalachians will continue bringing a deep
moisture fetch from the western Gulf over the area. Any convection
lingering at the start of the period will slowly sag south overnight
as the trough axis continues to push the wavetrain east. NAM keeps a
minimum of instability across the area with high pressure centered
over the Southeast ridging into the Piedmont, but the GFS is a
little faster with the approaching surface trough, allowing some
minimal instability across the Blue Ridge by midday, traversing into
the Piedmont during the afternoon. Very little shear to work with so
expect generally diurnal convective chances and as is typical cannot
rule out an isolated strong to marginally severe pulse storm, but
not particularly exciting. The upper trough axis pushes closer to
the area Tuesday night into Wednesday, but by Wednesday afternoon
the surface trough axis will have generally pushed through the
forecast area, leaving us in a minimum of instability. Shear will be
increased due to the proximity of the upper trough, but again
convective chances look diurnal at best, and more likely a little
less than. Temperatures through the period pretty close to seasonal
normals, perhaps only a degree or two off.


As of 210 PM Sunday: A broad upper trough remains over the East as a
closed upper low will remain located just north of the Great Lakes
Thursday.  The surface cold front is expected to pass south of our
area early Thursday with transit weak high pressure reaching the
mid Atlantic coast late Thursday. With this high moving offshore and
low level moisture increasing across the Gulf states with SW wind
behind the high, the front moves north as a warm front. This warm
front should reach the Virginias by Sunday and by that time we will
be deep in moist subtropical air. A series of shortwaves will be
advancing across the Plains States to the SE States in combination
with the persistent low level flow from the Gulf will keep a good
chance of convection in the forecast each day. The extensive
cloud cover will result in Max Temps bring held down a bit and Min
Temps being a few degrees above normal. Instability will be rather
low Thursday and then models bring CAPE values up to near 2000 in
the Piedmont over the weekend. As the general broad trough continues
over the East, the upper ridge will remain over the West.


At KCLT and Elsewhere: The first couple of hours or so of the
forecast period should be quiet. After that, confidence regarding
convective trends is not very high. Nevertheless, at least scattered
convection should develop across the area by late afternoon, and all
terminals get a VCSH at some point during the afternoon/evening. We
opted for VCSH because instability has been slow to recover, but
could have just as easily gone with VCTS. Tempo/s for TSRA may need
to be added with just a couple of hours notice, with KCLT being the
most likely site to see convection (which is reflected in some of
our newest high resolution model guidance), but again confidence
wasn`t high enough to go that route as of yet.

Otherwise, VFR is forecast through the period, other than perhaps
some mtn valley fog/low stratus possible Monday morning. Winds will
remain W/SW at generally 8-12 kts this afternoon, with some gusts
possible, esp across Upstate SC. Winds should then diminish to
4-8kts this evening.

Outlook: Thunderstorms and associated restrictions, mainly of the
afternoon/evening variety, as well as the potential for areas of
morning fog and/or low stratus will continue through at least the
end of the new work week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  98%     High  96%
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:




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