Severe Thunderstorm Warning 186, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
242 PM EDT Tue Jun 26 2018

.SYNOPSIS...
A stalled cold front will help generate another round of scattered
showers and thunderstorms this afternoon and evening. Additional
showers and thunderstorms are likely again on Wednesday and Thursday,
with hot weather returning to end the week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 2pm EDT Tuesday: Fairly general coverage of thunderstorms this
afternoon and Wednesday afternoon, with some severe gusts from storm
outflows and some possible hail in the strongest storms.  Wedge
boundary that preceded northeasterly flow this morning has largely
washed-out with northeasterly flow from wedge balanced against
southwesterly flow from broad area of low pressure to the west.
Early clouds have scattered and boundary layer has warmed enough to
give around 1000 j/kg of MLCAPE, with higher levels (to 3000j/kg
SBCAPE west of AVL). Wind shear is weak, but broad upper low
progressing across the central CONUS will help support storms
both today and tomorrow afternoon. As upper system moves
eastward, northeasterly wedge flow may resume overnight, giving
some low clouds and slightly cooler temperatures. However, wedge
should again wash-out Wednesday afternoon, and main impact of
wedge will be to reduce high temperatures today and tomorrow by
a couple degrees, down to about normal for this time of year.

Wind shear is weak this afternoon, with 15 to 20kts of deep
layer shear, improving on Wednesday to 30kts. Weakened shear
will make todays storms more pulsatile and less severe than
yesterday, though severe gusts in storm outflows are still
likely. With a little better shear on Wednesday, chances for
severe improve slightly. CAMS also have stronger updrafts
Wednesday afternoon, and forcing from progress of upper wave
also improves as primary lobe of PVA moves across.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 230 PM EDT Tuesday: Model guidance is in generally good
agreement on the placement of the upper-level trough axis, which is
directly overhead at the beginning of the period on Thursday night.
An attendant surface trough will be moving through at this time
as well.  Convection, some of which may be severe given 20-25
kts of deep-layer shear and the upper-level dynamics in place,
will be ongoing at this time and light shower activity may persist
into the overnight hours as moisture remains plentiful.

As the surface trough slowly pushes further east into central
NC during the day on Thursday, the westerly wind shift behind
the axis will introduce a modest downslope flow, which, when
combined with notable height rises aloft following the passage
of the upper trough, will result in a 3-6 degree increase in max
temperatures Thursday afternoon area wide and put us back above
normal for this time of year.  Unfortunately, dewpoints remain quite
uncomfortable (70-75 outside of the mountains) resulting in heat
indices approaching 100 along and S of the I-85 corridor.  However,
the column dries out considerably aloft as PWs drop towards 1-1.25
inches and model soundings suggest a modest warm nose or cap around
700-800mb.  Deep-layer, bulk shear values are also insignificant
at <10 kts.  Therefore, MUCAPE values may be high, but ultimately
any convection should be isolated in nature for Thursday.

The low-level pattern remains somewhat stagnant heading into
Thursday evening as the trough of lower pressure stalls over the
central Piedmont, as high pressure tries to build in upstream of the
parent low over New England.  The primary cold front which became
ill-defined over the western Appalachians, "reemerges" so-to-speak
to the lee of the mountains with winds veering northerly over the
NC mountains, foothills, and NW Piedmont overnight Thursday and NEly
into Friday morning.  Guidance is suggesting the potential for some
organized convection across central TN, N AL, and N GA possibly
extending east into our western-most counties overnight Thursday,
primarily along and to the west of the aforementioned frontal
boundary, which extends NW into the Ohio Valley as a warm front
ahead of a parent system over the northern Plains.  We shall see...

During the day on Friday, surface high pressure moves offshore while
the residual front transitions to a lee trough.  Friday convective
chances improve over the mountains and NE GA given modest increases
in PW values, less or little inhibition, and high SBCAPE combined
with typical orographic forcing, resembling a pulse-like pattern
with slow-moving convection producing a localized heavy-rain threat.
Meanwhile, the upper-level ridge axis advances east into the Ohio
Valley with a 591-594 dm center.  Therefore, given the heights
aloft and the fact that northerly flow behind the front really
isn't advecting cooler air, high temperatures on Friday remain hot.
The very faint silver lining is the northerly flow will usher in
slightly lower dewpoints/humidity for Friday, especially across
the NW Piedmont, but it will remain uncomfortable.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
As of 230 PM EDT Thursday: The upper ridge continues to slide
east heading into Friday with the center over the Mid-Atlantic
by Saturday evening as the next primary shortwave emerges from
the northern Rockies.  The area will remain within weak southerly
low-level flow both Saturday and Sunday which will allow diurnal and
pulse-like shower and thunderstorm activity to increase. Scattered
coverage is expected over the mountains, NE GA, and western SC
with lesser coverage further north and east, especially along
and E of I-77 closer to the subsidence max associated with the
upper-level ridge.

Our flow aloft will transition from Ely and SEly on the SW side
of the axis to NWly on the NE side of the ridge axis as the ridge
will dampen across the Northeast and Mid-Atlantic in response
to the wavetrain and retrograde south and west to expand across
the southern US heading into early next week.  A summerlike cold
front associated with the aforementioned shortwave will approach
the southern Appalachians Monday into Tuesday, increasing shower
and thunderstorm coverage area wide with likely PoPs over the
mountains and high-end chance elsewhere, peaking Tuesday as the
front arrives late Tuesday into early Wednesday.  Both high and low
temperatures remain 3-5 degrees above normal from Saturday through
Monday with humidity values persistently remaining uncomfortable
through the period.  Heat indices will stay at or below 100 during
the period but max temperatures will cool a few degrees in advance
of the cold front under increasing cloud cover on Tuesday.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Another round of thunderstorms this afternoon
and evening, with activity already beginning over the mountains, and
expected to spread over all areas over the next few hours.  Hi-res
model ensembles have showers mostly ending from the northwest to
southeast by 03Z.  This round of convection, and a similar round
Wednesday afternoon, is being assisted by the passage of an upper
wave across the north central CONUS which provides upper support.
Impact of wedge front has been minimal, as airmass has warmed to
produce typical amounts of instability for summertime afternoon
convection. Surface low associated with upper system has allowed
surface winds to become light southerly to southwesterly, against
the flow direction of wedge high pressure.  This has moved the
frontal zone northeastward, with mostly light and variable winds in
all areas.  Some northeasterly flow is expected to reassert itself
overnight with some return of wedge-like conditions with low
overcast Wednesday morning.

Outlook: A passing trough will enhance coverage of SHRA/TSRA again
Wednesday. Then another cold front will arrive from the northwest
on Thursday, although as a ridge builds over the East, hotter
but drier weather will return to end the 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...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High  84%     Med   77%     Med   78%
KGSP       High 100%     High  86%     Low   48%     High  85%
KAVL       High 100%     Med   70%     Med   71%     High  91%
KHKY       High  94%     Med   73%     Med   74%     High  82%
KGMU       High 100%     High  86%     Med   63%     High  91%
KAND       High 100%     High  80%     Low   59%     High  84%

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...JPT
NEAR TERM...WJM
SHORT TERM...JMP
LONG TERM...JPT
AVIATION...WJM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
521 AM EDT Tue Jun 26 2018

GAZ010-017-NCZ033-035>037-048>053-056>059-062>065-068-069-501>510-
270930-
Rabun-Habersham-Avery-Alexander-Iredell-Davie-Madison-Yancey-
Mitchell-Swain-Haywood-Buncombe-Catawba-Rowan-Graham-
Northern Jackson-Macon-Southern Jackson-Transylvania-Henderson-
Cleveland-Lincoln-Caldwell Mountains-Greater Caldwell-
Burke Mountains-Greater Burke-McDowell Mountains-Eastern McDowell-
Rutherford Mountains-Greater Rutherford-Polk Mountains-Eastern Polk-
521 AM EDT Tue Jun 26 2018

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina and western North Carolina.

.DAY ONE...Today and Tonight.

Scattered to numerous thunderstorms are expected to develop this
afternoon and evening. Some of these storms may become severe with
damaging winds as the main threat, but large hail cannot be ruled
out. Frequent cloud-to-ground lightning and brief heavy rain can be
expected as well.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

..Wednesday...No hazardous weather is expected at this time.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time.
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

GAZ018-026-028-029-NCZ070>072-082-SCZ001>014-019-270930-
Stephens-Franklin-Hart-Elbert-Gaston-Mecklenburg-Cabarrus-Union-
Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Chester-Greenwood-
521 AM EDT Tue Jun 26 2018

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina and upstate South Carolina.

.DAY ONE...Today and Tonight.

Scattered to numerous thunderstorms are expected to develop this
afternoon and evening. Some of these storms may become severe with
damaging winds as the main threat, but large hail cannot be ruled
out. Frequent cloud-to-ground lightning and brief heavy rain can be
expected as well.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

..Wednesday...No hazardous weather is expected at this time.
..Thursday...Excessive heat possible.
..Friday...Excessive heat possible.
..Saturday...No hazardous weather is expected at this time.
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

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