Severe Thunderstorm Warning 175, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
545 PM EDT Thu Aug 1 2019

.SYNOPSIS...
A persistent upper level trough will support afternoon showers and
thunderstorms into early next week. Deep-layered moisture will
increase Friday and linger...which will maintain the chance of
isolated flooding into Monday.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 540 PM EDT Thursday: Quick update to move around the
higher-than-normal precip chances through early evening based on
radar trends.  Temp/dewpt also modulated by the development and
movement of storms, so that will also be changed. Fcst looks good
overall, just has some of the details in the wrong spot.

Otherwise...same upper pattern in place with trough from the Great
Lakes into the Gulf, and ridging over the Desert Southwest and
Southern Plains as well as over the Western Atlantic. A stalled
front across the area continues to provide a bit of focus for
convective development, and little vort waves continue to ride up
out of the Gulf and over the area. Low level moisture advection
continues, and PWs will continue to climb this afternoon and
evening. Surface instability per mesoanalysis is over 2000J/kg just
about area-wide and of course convection fired first across the
mountains but seeing a blossoming of convection across the Piedmont
at AFD time. Steep low-level lapse rates and still some mid-level
dry air could lead to a few wet microbursts as was yesterday, and
have already issued a couple of SVRs. With increasing PWs and the
potential for training convection, even with steering flow allowing
for movement of storms, the heavy rain/isolated flash flood threat
will be higher today than yesterday, and WPC Marginal Risk looks
good. Convection may linger a little later tonight with another vort
lobe lifting up out of GA after 00z, and this is reflected in CAMs
with the HRRR and RAP both maintaining convection toward 06-07z.

As we move into tomorrow, a kink in the ridging expanding into the
Deep South col area will pull another vort lobe up into the area,
supporting even higher pops than today, but the trough will continue
to slide east so storm motion may adjust a little more to the E.
However, upslope low-level flow out of the SE will complicate
things as storm motion and storm propagation may work to almost
cancel each other out, so will have to reevaluate overnight as
that might lead to more flash flood potential. By tomorrow, the
profiles will be more moist so heavy rain will become an increasing
threat through the afternoon. With the increased cloud cover,
expect afternoon highs to be several degrees cooler than today,
a handful or so of degrees below seasonal normals.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 140 PM Thursday: The upper patter remains in a broad trof
config with pockets of vort energy traversing the flow. There are
sigfnt differences showing up Sun as the 12z NAM generates an upper
low across the Midwest and increases deep lift and thereby a creates
higher than normal stg/svr tstm potential across the FA thru the
day. This feature is not seen in the other op models...so little
weight will be given to this probability.

With the subTrop high remaining centered well off the Atl coast...a
high theta/e airmass will be maintained over the SE CONUS. The
latest GEFS shows increasing positive PWAT anomalies pushing toward
the SE coast Sat...however the FA will likely see moisture levels
reach just abv normal levels over the weekend. So...with the
persistent e/ly flow in the h92-h85 layer...will expect better
convec chances across the higher terrain once again. Not seeing an
issue with widespread flooding as the Balsams and srn BR will get
the brunt of the higher rainfall. A storm total QPF showed the srn
NC mtn ridges receiving just under 2.0 inches...thus isol hydro
issues look to be the main threat.

Otherwise...expect pulse stg/svr convection building on new and
existing outflow bndrys each afternoon....similar to the afternoon
pattern seen the past few days. The atmos remains conditionally
unstable thru the overnight periods with no good potential of
sfc-based inversions nor mlvl capping...so lingering isol -shra with
a few weak tstms will possible into the early morning hrs. Max and
min temps will hover right arnd normal levels each day.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 230 PM Thursday: No big changes were made to the ext range
fcst. The upper level trof will continue to dominate the pattern
while a weak pressure gradient persists at the sfc. There does look
to be some movement with the upper trof axis by Tue as the GFS is
indicating a transition to deep layered subsidence while the flow
becomes more w/ly in the low-levels. This scenario doesn/t look to
offer much more than a mix of lower theta/e air across the far nrn
zones...so still expect a modified persistence type fcst day-to-day
thru the period featuring afternoon isol/sct pulse convec. The hydro
threat will lower somewhat during this time as PoPs have been
lowered closer to climo. Max and min temps will remain close to
normal with high sfc dewpoints maintaining muggy feeling conds.

&&

.AVIATION /22Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Took some time for the fog to lift this
morning, but VFR everywhere at TAF time. TSRA popping across the
mountains and beginning to fire across the Piedmont, especially the
Upstate, so have VCTS for all but KCLT and best timing of TEMPO TSRA
starting between now and 20z. Concerned that another surge of
moisture and upper energy may result in a later max in coverage,
with some TSRA even lingering toward 03-04z, so TEMPO timing will
likely have to be adjusted depending on how the convection evolves
this afternoon and evening. More cloud cover may act to somewhat
limit some of the overnight mountain valley fog/low clouds, but have
continued previous trend at KAVL and added some MVFR fog mention to
KHKY to hint that the increasing surface moisture may result in
restrictions outside the mountains, will need to be reevaluated for
the 00z TAFs. Convective chances greater tomorrow than today and
could get an earlier start, so have already introduced PROB30s and
even prevailing TSRA in the out periods at KCLT. Winds on the S side
this aftn/eve, lgt/vrb overnight, and some question about NE or SE
winds tomorrow but have stayed on the SE side for now.

Outlook: The stalled cold front will continue to result in elevated
chances for scattered diurnal showers and storms/associated
restrictions into the weekend, as well continued potential for
morning low stratus and/or fog.

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  98%     High  96%
KAVL       High 100%     High 100%     Low   41%     High  96%
KHKY       High 100%     High 100%     High  98%     High  93%
KGMU       High 100%     High 100%     High  98%     High  96%
KAND       High 100%     High 100%     High 100%     High  96%

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...SBK
NEAR TERM...PM/TDP
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
441 AM EDT Thu Aug 1 2019

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-020845-
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-
441 AM EDT Thu Aug 1 2019

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

.DAY ONE...Today and tonight.

Scattered thunderstorms are expected across the western Carolina's
and northeast Georgia this afternoon to evening. A few of the storms
will be strong to severe with small hail and damaging wind possible.
Heavy rainfall with localized flooding will also be possible,
especially this evening into tonight.

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

Scattered to widespread showers and thunderstorms are expected Friday
afternoon into Friday night and again Saturday. A tropical airmass in
place will support periods of heavy rain with localized flooding
likely, especially from the I-77 corridor, including Charlotte,
northwest into the North Carolina foothills.

.SPOTTER INFORMATION STATEMENT...

None.

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