Severe Thunderstorm Warning 179, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
446 PM EDT Thu Jul 13 2017

.SYNOPSIS...
Hot and humid conditions will persist into the weekend, with
scattered to numerous afternoon and evening thunderstorms each
day. A cold front will move into the region from the northwest
on Saturday and stall in or near the area through Sunday.
Another cold front will approach on Monday and move southeast
of the area on Tuesday, with drier conditions arriving by the
middle of next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 445 PM EDT: Made some minor tweaks to the PoPs and T/Td trends
for the next few hours to line up with latest obs/sat/radar. Like
yesterday, convection is generally remaining sub-severe. But gusty
winds, frequent cg-lightning, and locally heavy rain threats exist.
Temps are running a deg or two warmer than yesterday in most spots,
also resulting in heat index values in the 95 to 100 deg range late
this afternoon.

As of 200 PM EDT Thursday: Upper ridge continues over the Carolina
coast, with a weakness lifting out of the Gulf into the Lower MS
Valley. Meanwhile a shortwave is working its way across the eastern
Great Lakes around the Canadian longwave trough, while a cutoff
upper low is pushing into the western Great Lakes. Associated
surface low over MI at AFD time has trailing cold front extending
WSW toward the OK Panhandle. Southerly surface flow around the
western periphery of the Atlantic high will continue to bring low-
level WAA toward the Southern Appalachians, enhanced in part by the
Lower MS Valley weakness. Lee troughing and orographic lift plus the
approaching front will continue to be players this afternoon, with
best convective chances remaining across the mountains and adjacent
foothills. Weak steering flow may lead to localized heavy rainfall
concerns. Though sbCAPEs >2000 J/kg and low-level lapse rates are
certainly supportive of Piedmont convection, weak mid-level lapse
rates and lower 850mb RH will continue to inhibit widespread
convection, though with dCAPEs >1000J/kg over the Piedmont,
anything that does develop could contain some gusty winds.

As we move through the near-term, the western cutoff and upper
trough will work east toward Quebec, pushing the front through the
OH Valley. The Southeast upper ridge will break down somewhat and by
the end of the period the front will be working its way across the
area, weak though it may be. Should see increased convective chances
by Friday afternoon (though still with the max over the mountains)
and with the elongated area of upper vorticity approaching as well,
the Day2 Marginal Risk for the northern tier seems warranted as mid-
level lapse rates should improve leading to a low-end wind threat.

Besides the convective activity, above-normal temperatures remain
the concern. Really we're only talking a couple of degrees above
seasonal normals, though with dewpoints hovering around 70 across
the Piedmont, but pooling into the mid 70s toward the foothills,
heat indices will continue to flirt with the century mark, with a
few locations sneaking above it. Still a few degrees below heat
advisory criteria but worth taking standard heat safety precautions
nonetheless.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 210 PM EDT Thursday: Heights fall slowly but steadily through
the weekend as a trough builds over the eastern CONUS. A weak short
wave drops into the trough and crosses the area Saturday while a
stronger, but still relatively weak, short wave does the same on
Sunday. A weak cold front moves in from the NW Friday night and
stalls across the area on Sunday. The front weakens Sunday as it
slowly moves into the southern portions of the CWFA. Upper level
divergence increases as the right entrance region of the an upper
jet slides south into the area. These features will provide more
forcing for convection than the previous few days. Instability
remains moderate to very high both days but will be on the downward
trend. Shear increases with the short waves but remains below 30
kts. There will be less mid level dry air as well with an increase
in deep layer moisture and PW values near 2 inches. Although, DCAPE
values remain relatively high. Therefore, expect better coverage of
convection CWFA wide Saturday with a focus across the southern CWFA
for Sunday. Severe storm chances will be similar with a marginal
threat CWFA wide Saturday and the threat shifting to the southern
CWFA on Sunday. The heat begins to abate with falling thicknesses
for the weekend. The highs Saturday will be closer to normal but
high humidity will put heat index values near 100 along and south of
the I-85 corridor. Temps fall below normal for Sunday but heat index
values linger in the 90s. Lows remain above normal but with a
cooling trend.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 205 PM EDT Thursday: the extended fcst picks up at 00z on Monday
with a positively tilted upper trof digging down across the Great
Lakes and broad upper ridging persisting across the western 2/3 of
the CONUS. Over the next couple of days, the upper trof axis will
move over the fcst area as the ridge gradually expands eastward.
Beyond this point, the long range models diverge wrt the trof. The
GFS tries to cutoff the trof over the CWFA on Wed and keep the ridge
from advancing into the fcst area. The ECMWF, on the other hand,
moves the trof offshore and spreads the ridge over the area on Wed
and Thurs. At the sfc, a reinforcing cold front will move over the
fcst area on Monday and stall just to our south before dissipating
on Tuesday. As we go into mid-week, high pressure strengthens to our
NW and moves over the region to end the period. As for the sensible
fcst, no significant changes were made with solid chances for
widespread diurnal convection over the CWFA on Monday and slight to
solid chances for Tues. Wed should be quieter with the center of
the sfc high just to our north. Temps are also expected to start out
right around normal and slowly climb thru the period, yet they are
not fcst to reach heat advisory criteria at this time.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: Convection will increase this afternoon
mainly across the mountains, and have continued VCTS for KAVL and
KHKY. For all other sites, chances too low to include at this time,
but will continue to monitor in case something needs to be added.
Cannot rule out mountain valley restrictions overnight, including at
KAVL, and though the KAVL TAF only includes MVFR conditions, could
easily drop to LIFR again. As the front approaches tomorrow,
convection will increase again but mainly after 18z, so PROB30 only
introduced at KHKY and KAVL.

Outlook: Scattered to numerous afternoon and evening convection is
expected each day through Monday across the area, with higher
coverage in the mountains. Morning fog development can be expected
in mountain valleys and areas that receive rainfall in the previous
afternoon.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  93%     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...JPT
NEAR TERM...ARK/TDP
SHORT TERM...RWH
LONG TERM...JPT
AVIATION...TDP

Hazardous Weather Outlook...CORRECTED
National Weather Service Greenville-Spartanburg SC
514 AM EDT Thu Jul 13 2017

GAZ010-NCZ033-048>053-058-059-062>065-501-503-505-507-509-140915-
Rabun-Avery-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Graham-
Northern Jackson-Macon-Southern Jackson-Transylvania-Henderson-
Caldwell Mountains-Burke Mountains-McDowell Mountains-
Rutherford Mountains-Polk Mountains-
514 AM EDT Thu Jul 13 2017

This Hazardous Weather Outlook is for Rabun County in northeast
Georgia and the mountains of western North Carolina.

.DAY ONE...Today and Tonight.

Scattered to numerous thunderstorms will develop across the region
this afternoon and evening. Any of these thunderstorms may produce
locally heavy rainfall, cloud-to-ground lightning strikes, and
briefly gusty winds. A few of the thunderstorms may produce
damaging wind gusts of 60 mph or greater. Isolated flooding could
also occur under slowly moving thunderstorms or in areas impacted
by repeated thunderstorms.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

..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.
..Tuesday...No hazardous weather is expected at this time.
..Wednesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

GAZ017-018-026-028-029-NCZ035>037-056-057-068>072-082-502-504-506-
508-510-SCZ001>014-019-140915-
Habersham-Stephens-Franklin-Hart-Elbert-Alexander-Iredell-Davie-
Catawba-Rowan-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-
Greater Caldwell-Greater Burke-Eastern McDowell-Greater Rutherford-
Eastern Polk-Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Chester-Greenwood-
514 AM EDT Thu Jul 13 2017

This Hazardous Weather Outlook is for northeast Georgia, the
foothills and piedmont of western North Carolina and Upstate South
Carolina.

.DAY ONE...Today and Tonight.

Isolated to scattered thunderstorms will develop across the region
this afternoon and evening. Any of these thunderstorms may produce
locally heavy rainfall, cloud-to-ground lightning strikes, and
briefly gusty winds. A few of the thunderstorms may produce
damaging wind gusts of 60 mph or greater. Isolated flooding could
also occur under slowly moving thunderstorms or in areas impacted
by repeated thunderstorms.

In addition, high temperatures of 90 to 95 degrees this afternoon
will combine with humid conditions to produce Heat Index values of
100 to 104 degrees in many foothill and piedmont locations.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

..Friday...Excessive heat possible. Afternoon Heat Index values
between 100 and 105 are 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.
..Tuesday...No hazardous weather is expected at this time.
..Wednesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

HG

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