Severe Thunderstorm Warning 213, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
502 PM EDT Wed Jun 27 2018

.SYNOPSIS...
Strong to severe thunderstorms will persist into this evening but
activity will dissipate overnight.  A weak cold front approaches the
area Thursday and additional showers and thunderstorms are expected.
Behind the front, precip chances decrease through Saturday but heat
and humidity will persist.  Shower and thunderstorm chances increase
Sunday through Wednesday as another front approaches the area.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 500 PM: Minor adjustments made to temperatures/winds to
coincide with latest trends as the rest of the near term forecast
remain on track.

Showers and thunderstorms continue to push across portions of the
area attm, mainly northeast GA and the Upstate - a few of these
storms do have a history of producing damaging winds and hail.  A
Severe Thunderstorm Watch remains in effect for portions of our area
through 9 PM.

Otherwise, an upper trough will move over the lower Ohio Valley
tonight and early tomorrow as a sfc cold front moves thru the area.
Max temps today should top out around normal for late June with
highs tomorrow reaching a few degrees above normal. Tomorrow should
be less active overall with drier profiles in place and more of a
downslope component to the low-lvl flow. In addition, the upper trof
axis should be east of the CWFA by tomorrow afternoon. Thus upper
lvl support will be considerably weaker over the area.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 230 PM EDT Wednesday: We are still on track to welcome
another weak frontal boundary into the region Thursday night
into early Friday as the upper level trough axis exits the East
Coast.  Surface winds will veer from westerly to northerly and
northeasterly as the front drops from north to south through our
area, clearing the region later Friday morning as high pressure
builds into the Mid-Atlantic.  The long-advertised heat ridge
enters the mid-Mississippi River Valley behind the departing
trough which will allow us to maintain min and max temperatures
about 4-8 degrees above normal; however, the northerly low-level
flow will allow slightly drier air (dewpoints in the upper 60s)
to infiltrate the region and reduce humidity.  Subsidence-induced
warm air continues to be advertised in the 600-800mb layer aloft
which will aid in suppressing convective activity across much
of the Piedmont.  Regardless, we continue to carry a chance of
convection along our southern and western counties closer to the
frontal boundary and over the mountains where typical orographic
forcing is anticipated to overcome the weak cap.

Northeasterly near-surface flow continues into Saturday as high
pressure slowly moves off the Delmarva coastline, keeping us along
the ridge axis.  Aloft, the heat ridge centers over the Mid-Atlantic
and the low to mid-level flow veers easterly, which appears to
advect some Atlantic moisture into the region, especially along
the southern and western counties, and the column moistens below
600mb in response.  Some mid-level inhibition via the subsident warm
nose remains but the "moist" easterly flow combined with respectable
MUCAPE values increases diurnal PoPs slightly on Saturday especially
south and west, furthest away from the upper-level ridge center.
There will be little change in temperatures and a slight uptick in
humidity, especially across the NC Piedmont which will keep heat
indices in the upper 90s to near 100, but below advisory criteria.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 230 PM EDT Wednesday: As the upper-level ridge center slides
off the East Coast heading into Sunday, the Deep South is in a
weakness between that center and a second height maximum over the
the Southern Plains.  One or two weak upper lows may develop in
this weakness which may enhance moisture flux and forcing Sunday
into Monday, but overall the general pattern will not change as
southeasterly low-level flow will persist around the base of the
high pressure center over the western Atlantic.  Persistent moisture
flux into the region combined with upslope flow will incrementally
increase PoP on Sunday and Monday as mid-level subsidence warming
weakens and total moisture content in the column increases.
Overall, we are expecting flow throughout the column to be very
weak which means as PWs increase to above 1.50" Sunday and Monday
the threat for locally heavy rainfall and isolated flooding will
also increase.

The most significant change in the pattern for Tuesday and
Wednesday is the approach of another weak/summertime cold front
which is associated with a weak shortwave trough.  The trough
will concurrently dampen the East Coast ridge.  Guidance is in
generally good agreement on this frontal approach and the area-wide
increase in PoPs as the associated forcing influences coverage.
As the parent low departs New England heading into Wednesday the
front may wash out before it reaches our area but the proximity
of the remnant boundary will maintain high-end chance (Piedmont,
foothills) to likely PoPs (mountains) into Wednesday afternoon.
Overnight PoPs during Tuesday and Wednesday night will remain
elevated given the moisture and weak forcing in place.  The heavy
rainfall threat also persists as the mid-level flow from Monday
weakens further in advance of the shortwave trough.

There will not be much change in above-normal temperatures or
muggy dewpoints during the period; however, the increase in cloud
cover Tuesday and Wednesday as a result of increased convective
coverage will shave 1-3 degrees off the highs both days returning
us to near-normal temperatures for early July.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: Expect mostly VFR conditions to prevail thru
18z TAF period. Exceptions include TEMPOs for TSRA this afternoon
and evening with another round of reduced visby for KAVL tomorrow
morning from roughly 10 to 13z. I have visby going down to MVFR at
KAVL, but they could see brief IFR visby and cigs as well. Otherwise,
we can expect another round of scattered to numerous showers and
thunderstorms this afternoon/evening with some organization possible
especially across the Foothills and Piedmont. Convective potential
dwindles after roughly 00z, although some activity could linger into
the late night and overnight. Tomorrow should be less active overall
with drier profiles in place and less upper-lvl support over the area.

Outlook: An upper ridge building over the Eastern CONUS is expected
to reduce diurnal convection late this week into early next week.
Patchy morning fog and/or low stratus will continue to be an issue
in mountain valleys and/or locations with wet ground.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 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 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...JMP
NEAR TERM...JPT/SGL
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...JPT

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