Severe Thunderstorm Warning 115, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
228 PM EDT Tue Jun 13 2017

.SYNOPSIS...
Subtropical high pressure centered to our east will weaken through
mid week, allowing deep moisture to spread over the forecast area
from the south. Chances for showers and thunderstorms will increase
each day through the work week and remain elevated through the
weekend. A more well-defined cold front is expected to approach the
area early next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 220 PM: The southeastern states remain under a broad upper
ridge, but a weakness exists in the form of a shallow sfc/upper
trough extending down the East Coast from a low over the Canadian
Maritimes. A small vort max is present over VA/NC as well. Despite
the enhancing effect of the trough, convection so far today has
been mainly associated with the high terrain. Steering flow is
weakly from the NW in this area, so it is logical that the model
consensus is for some of the activity to move off the ridges and
gradually into the Piedmont with time. Fairly high LCLs and DCAPEs
exist, and in light of weak shear these are marginally supportive
of severe downbursts, but so far no cells have had a sufficiently
strong updraft for such. Nonetheless, over the course of the aftn
outflow boundaries should focus new development. The suite of meso
models shows a couple hours' variation in how quickly things fizzle
out after the loss of heating. The NAMNest is on the faster side,
and its depicted coverage is verifying fairly well so far. However,
I am reluctant to trend PoPs down very quickly given the expectation
of lingering outflows. Some fog is likely to develop tonight in the
mountain valleys and where heavy rain falls this aftn...too early
to say with certainty exactly where. Profiles certainly are not
supportive of widespread fog so it should remain rather localized.

Heights continue to fall over the Mid-Atlantic as the aforementioned
shortwave/vort max shifts east, but rise a bit over us. The
low-level flow backs to NW as ridging tries to build in. Overnight
this NW flow could fire a few showers/storms near the Tenn
border, so a small PoP returns in the early morning up there. That
shortwave, in conjunction with continued westerly flow across the
Appalachians, appears to keep the trough in place for Wednesday.
Lapse rates will be modest and similar to those today. Hence
convective potential is similar as are PoPs. Modeled DCAPE values
however are notably larger which implies greater downburst risk
under still weak shear. SPC Day 2 outlook covers most of the CWFA,
excluding our southwest and far south, in a Marginal Risk area.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 115 PM EDT Tuesday: Moisture, instability, forcing, and the
resulting convective coverage, will gradually increase Thursday
through Friday. As the upper ridge over the southeast starts to
break down on Thursday, upstream shortwave energy will stand a
better chance of reaching the southern Appalachians by peak heating
Thursday afternoon. Better upper-level troughiness will then develop
between the Mississippi River Valley and the Appalachians by Friday.
The pattern of mainly diurnal convection will continue during this
late week period, with a steady uptick in convective coverage and
intensity as lapse rates steepen a bit and surface-based CAPE values
reach 2000 to 2500 J/kg across more of the area. Flow up the column
will remain light through the period, but the boundary layer flow
will become more southerly with time. This will increase moisture a
bit as precipitable water values exceed 1.5 inches in the mountains
and approach 2 inches in southeast sections. This will increase the
localized heavy rain threat as well. Coverage should also become
more expansive outside of the mountains on Thursday and Friday
afternoons as west to southwest flow increases slightly aloft.
Expect overnight min temps at least two categories above climo, with
afternoon maxes at least a category above climo eacy day.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 200 PM EDT Tuesday: The work week will end with a fairly weak
pressure pattern over the southeast as a wave rounding an upper low
centered over southern Ontario provides some weak upper level
forcing close to the spine of the Appalachians. This will aid the
development of mainly diurnally-driven showers and thunderstorms
Friday night. Deep, moist southerly flow with a decent Gulf fetch
will continue through the weekend as heights begin to fall aloft. PWs
will remain 1 to 2 standard deviations above normal through early
next week...and storms should have good coverage each afternoon over
the weekend and be relatively efficient rain-producers considering
the moisture profiles and deep warm cloud layers. Though the showers
and thunderstorms will be convective...there could be an isolated
flash flood concern by the end of the week if showers and storms can
train over the same areas over multiple days. Pops will remain above
climo both Saturday and Sunday.

By Monday, a more substantial shortwave will be rounding the
longwave trough deepening over the east coast...and a more defined
front may be able to push through the area Monday night and Tuesday.
The falling heights and resulting QG forcing for ascent over much of
the area should lead to good coverage of showers and thunderstorms
Monday afternoon and evening...and pops were increased even more
above climo, though they were capped in the likely range. Whether or
not this frontal passage is clean remains to be seen, as there are
some model disagreements over the depth of the east coast trough and
just how progressive the pattern will be. Temperatures will be
remain about 5 degrees above average through Monday before dropping
to near climo on Tuesday as the upper level trough sits over the
eastern half of the CONUS.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
At KCLT this aftn: Chances for convection this aftn appear no
greater than previously anticipated. Consensus of guidance is for
a cluster of activity to form along outflow boundary over the NC
Foothills and NW Piedmont, which will peak in intensity before
it reaches the field. Nonetheless the outflow may bring brisk NW
gusts and some new TS will continue to fire along the boundary
until early evening.

Otherwise: TEMPO TSRA at all terminals except KAND this aftn;
KAND is a bit more removed from the high terrain where the most
widespread convective initiation will occur. Any TSRA will be
capable of gusts above 20KT and brief vsby restrictions. Though sfc
dewpoint depressions will be small tonight, and crossover temps
fairly high, models mostly exhibit dry boundary layers above the
sfc. Given unfavorable profiles and patchy midlevel cloudiness I
only have the confidence to fcst fog at KAVL tonight, given its
valley location. Patchy fog will develop wherever heavy rain falls
from this aftn's storms but it is too early to tell which (if any)
terminals will experience a direct hit. Winds will mainly be SW,
but lee troughing should begin to back those to SW in the Piedmont
(incl KCLT) by midday.

Outlook: Improving boundary layer moisture combined with a weakening
upper ridge will lead to increasing chances for SHRA/TSRA each
day this week. Morning visibility restriction chances will also
increase, mainly in the mountain valleys, but also is possible
outside of the mtns where any precipitation has recently occurred.

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  90%     Med   79%
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...Carroll
NEAR TERM...Wimberley
SHORT TERM...HG
LONG TERM...Carroll
AVIATION...Wimberley

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
449 AM EDT Tue Jun 13 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-140900-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Rowan-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Chester-Greenwood-
449 AM EDT Tue Jun 13 2017

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

.DAY ONE...Today and Tonight.

Isolated to scattered thunderstorms are expected to develop across
the area this afternoon into the evening. While the main threats will
be from cloud to ground lightning and locally heavy rainfall, a few
of the storms could produce brief severe weather in the form of
damaging wind gusts and hail to the size of quarters.

.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...

None.

LANE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
409 PM EDT TUE JUN 13 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0400 PM     HAIL             4 SE HICKORY            35.70N 81.27W
06/13/2017  E1.00 INCH       CATAWBA            NC   BROADCAST MEDIA

            QUARTER SIZE HAIL REPORTED ALONG HIGHWAY 70 NEAR HICKORY
            MOTOR SPEEDWAY.

&&

HG

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