Severe Thunderstorm Warning 216, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
235 PM EDT Tue Jul 18 2017

.SYNOPSIS...
A stalled frontal boundary will slowly dissipate over the next
few days as a strong upper ridge gradually builds into the region.
This will bring hot temperatures and a reduction in the coverage of
diurnal showers and thunderstorms through the end of the work week.
Temperatures will begin to moderate by the weekend while enhanced
thunderstorm chances return to the forecast early next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 230 pm EDT: A closing upper-level low pressure system will
migrate slowly east across the piedmont and coastal plain of the
Carolinas tonight through Wednesday. Meanwhile, heights will
steadily recover from the west. A weak vorticity lobe is crossing
the mountains on the back side of the main trough late today and
this feature, along with weak upslope flow, is generating scattered
afternoon convection along and east of the Blue Ridge. Relatively
good surface DCAPEs and 25+ K surface to mid level theta e lapses
will provide decent gusts with any thunderstorms. After the
afternoon convection wanes, PoPs will diminish greatly later this
evening and overnight, with the main overnight issue likely being
low clouds and fog in the mountain river valleys. Low clouds east of
the mountains should be less widespread given the slightly drier
boundary layer.

On Wednesday, profiles exhibit less instability, lapse rates are
more modest, and triggering should be weaker. Scattered ridge top
coverage still seems likely as sbCAPE rebounds to 1500+ J/kg in many
areas. 850 mb flow will acquire a light downsloping component to
further limit PoPs east of the high terrain. Anticipate max temps
another 2 degrees above current day maxes, with Heat Index values
likely reaching the upper 90s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 230 PM EDT Tuesday:  The short term fcst period kicks off on
Wednesday evening amidst gradually building heights from the west
as a large upper anticyclone strengthens over the plains, while an
H5 depression/low slowly meanders along the Carolina coastline.
At the surface, high pressure anchored over the western Atlantic
will remain dominant, likely suppressing convection to some degree.
With that, the fcst will kick off to feature low end pops,
mainly along the high terrain where inhibition will be weakest.
Said pops will taper into the overnight leading into a dry fcst for
Thursday morning.  By that time the upper ridge will have shifted
over the MidSouth region with enough warming aloft to suppress
convection across much if not all of the fcst area for Thursday
therefore pops will remain below mentionable levels.

Meanwhile, the aforementioned H5 depression is progged to
retrograde westward along the SC/FL coastline, eventually moving
inland by Friday.  This feature looks to complicate fcst somewhat
as it pertains to excessive heat, especially on Friday when the
upper ridge weakens slightly as these two features interact.
As a result, fcst pops will be slightly higher on Friday as deep
subsidence is weaker across the mtns/fthills, however remaining dry
over the piedmont.  As for temperatures and heat indices, expecting
highs in the lower/mid 90s across the low terrain, with upper 80s in
the mtn valleys on Thursday.  Further warming is fcst on Friday when
maxes push into the mid/upper 90s for the low terrain, while lower
90s are favored in the mtn valleys.  Given very moist dewpoints
and minimal mixing, heat index values for Thursday and Friday will
be critical, with values approaching 100 and 105 respectively,
the highest of those indices to be observed along/south of I85.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
As of 230 PM EDT Tuesday: Large shifts in the guidance with this
medium range package. Previous forecasts hinged on the expansion of
a strong upper level ridge into the southeast as an upper level
trough axis shifted eastward into the Atlantic. For the latest
cycles though, all major models are now showing the upper trough
over the east coast pinching off an upper level disturbance that
hangs over the southeast and migrates towards the Gulf coast through
the weekend. This will prevent major height rises over the weekend,
so temperatures were trimmed down a few degrees on Saturday and
Sunday, while pops were raised to come closer to climo. Upper level
troughing will return early next week, and with it more moderate
temperatures and a surface front that will provide a focus for some
enhanced diurnal convection, especially Tuesday afternoon.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Convection has thus far has been confined to
the immediate Blue Ridge area this afternoon, but the convection
allowing models bring some of this activity east over the foothills
and into the piedmont through early evening. TSRA chances will be
best from KAVL to KHKY, but will continue to ride on TEMPO TSRA at
KCLT given the light northwest steering flow. Will maintain VCTS at
the Upstate sites. The mountain valleys will once again see the best
chance of low clouds and fog, but less difficulty is expected east
of the mountains where the boundary layer will be a bit drier. Will
keep the forecast dry through 18Z Wed with any isolated to scattered
mountain storms expected later in the day. Light winds will remain
mainly southerly, turning more westerly on Wed.

Outlook: Isolated to scattered afternoon and evening thunderstorms
are expected on Wednesday, with better coverage over the mountains.
Morning fog development can be expected in the mountain valleys and
in areas that receive rainfall the previous afternoon/evening. Drier
air will likely limit convective coverage for Thursday, with typical
mid-summer conditions returning by Saturday.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High  94%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  97%     High  91%     High  94%
KHKY       High 100%     High 100%     High  97%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  91%     High  94%

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...HG
SHORT TERM...CDG
LONG TERM...Carroll
AVIATION...HG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
651 AM EDT Tue Jul 18 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-191100-
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-
651 AM EDT Tue Jul 18 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 again
across the area this afternoon and evening. The main threats will be
from cloud to ground lightning and locally heavy rainfall. However,
a few storms could become briefly severe, with damaging winds being
the primary threat.

.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

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