Severe Thunderstorm Warning 145, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
454 PM EDT Sun Jun 21 2020

.SYNOPSIS...
Warm temperatures with afternoon and evening storms can be expected
through the first half of the week. An approaching front will
impact the area during the middle part of the week, enhancing
the coverage of storms. Drier air filters in from the north for
Thursday through the end of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
500 PM Update...No big changes to the grids. Showers and tstms are
having a hard time developing this afternoon due to an ulvl ridge
centered across the region. Expect continued sub-severe pulse
storms to develop mainly across the srn NC mtns thru the next
update.

As of 155 pm: A short wave ridge centered over the heart of the
forecast area appears to be doing its part in suppressing deep
convection across the forecast area this afternoon. Having said
that, because it's late June (the atmosphere has managed to
destabilize to the tune of 1500-2000 J/kg of sbCAPE) and we are
talking about the southern Appalachians here...a few isolated cells
have managed to fire across the NC mtns. As the ridge scoots east
this evening, and a dampening short wave trough...currently over the
TN Valley skirts by the Appalachians in its wake, coverage of
mountain convection is actually expected to reach its peak until
early this evening, when solid chance...if not likely pops appear
warranted. Chances also increase to 20-30% across the Piedmont this
evening, as outflow boundaries from mountain convection push
southeast off the Blue Ridge. A combination of seasonably high
levels of instability, robust downdraft CAPE, and weak shear will
pose the potential for 1 or 2 of the stronger storms to produce wet
microbursts. Convection is expected to steadily diminish from
mid-evening on, with only token 10-20 pops advertised after
midnight. Min temps will be slightly above normal, and early morning
fog and low stratus should again be primarily confined to the
mountain valleys.

Monday will see another typical early summer day, with seasonal
levels of humidity/instability in a slightly-warmer-than-normal
temperature regime. Having said that, short term guidance depicts
another short wave ridge influencing the area tomorrow, and in
general, guidance is not too excited about convective chances until
toward evening. Even at that, short term convective qpf and CAMs
simulated reflectivity generally keep convection confined to far
western areas. As such, diurnal pops will again peak more toward
Monday evening, and range from 40-50% across the western half, to
20-30% across the east.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 150 PM EDT Sunday: Tuesday thru Wednesday look like
the most active period of the week, as a deep longwave trough
persists across the Great Lakes to the TN Valley. A series of
vort maxes/MCVs will rotate around the base of the trough and
cross the FA during this period, it's difficult to time individual
waves this far out. Meanwhile, a cold front will sag SEWD across
the OH Valley Tuesday, and should push into the forecast area on
Wednesday. Increasing deep-layer WLY to WSWLY flow will result in
an uptick in bulk shear (20-30kts) and bring a plume of higher
PWATs. The deeper moisture will likely result in more cloud
cover, and the 12z NAM has really backed off the high CAPE as
a result. Models are in relatively good agreement on 1000-2000
J/kg of sbCAPE both days. So still expect above climo coverage of
convection, but severe threat is still a bit up in the air. Think
there will be a few pulse severe storms both days, but whether
anything more organized gets going remains a question. The NAM hints
that some sort of MCS may develop to our west Tuesday and could
affect the forecast area Tuesday night or Wednesday. But confidence
still too low to mention in the HWO at this time. Wednesday is even
more uncertain, given the expected cloud cover as the front pushes
in (and possibly early arrival of upstream convection). PoPs will
feature a gradient from chc east to categorical along the TN border
Tuesday. The entire area has a likely PoP for Wednesday. Max temps
will be near normal Tuesday, and a category or so below normal
Wednesday. Min temps will be slightly above normal both Monday
and Tuesday nights and near normal Wednesday night.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 220 PM EDT Sunday: The medium range guidance has come into
better agreement on pushing the cold front thru the area by Thursday
aftn, resulting in a couple of relatively dry days for the forecast
area. As the axis of an upper trough swings thru the region, temps
should be near normal with slightly lower dewpts both Thursday
and Friday with only some slgt chc PoPs (Piedmont Thu and in the
Mountains Fri). From there the GFS and ECMWF start to diverge a
little bit on the upper pattern. The GFS builds a stronger ridge
over the Southeast, while the ECMWF breaks the ridge down with a
northern stream trough by Sunday. This doesn't seem to have much
impact on our sensible wx though, as both show typical diurnal
mainly mountain convection and a Bermuda high sfc pattern across
the region. Temps will likely be above normal with highs in the
lower 90s and lows in the lower 70s across the Piedmont.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Afternoon convection is behaving more or less
as expected so far, with coverage being considerably lower than in
recent days at this time, owing to the presence of an upper ridge.
Nevertheless, there's enough activity to warrant a VCTS at KAVL
through much of the afternoon, as coverage should gradually expand,
and is not expected to peak until probably early evening, when the
ridge will begin shifting east, followed by an approaching upper air
disturbance. At least isolated convection will be possible near all
terminals from late afternoon through the evening. Coverage is not
expected to be sufficient to warrant a VCTS/VCSH outside of KCLT,
but this may change as the afternoon wears on. Otherwise, convection
should diminish from mid-evening on. Late night/early morning fog
and low stratus should be primarily confined to the mountain valleys
again.

Outlook: Diurnal convection in line with summer climatology
is expected again on Monday. An uptick is possible on Tuesday
into Wednesday as a frontal zone arrives from the west. Flight
restrictions will be possible each day in any afternoon/evening
thunderstorms, and also in low clouds and fog around daybreak
each morning.

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 100%     High 100%
KAVL       High 100%     High 100%     Low   26%     High  96%
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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

SYNOPSIS...ARK
NEAR TERM...JDL
SHORT TERM...ARK/SBK
LONG TERM...ARK
AVIATION...JDL

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
457 PM EDT Sun Jun 21 2020

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-222100-
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 NC-
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-Union SC-Chester-Greenwood-
457 PM EDT Sun Jun 21 2020

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

.DAY ONE...Tonight.

Isolated to scattered thunderstorms will continue to develop into
the evening. Coverage of storms will be better across the mountains.
A few of the storms could become severe with damaging wind gusts and
large hail. Heavy downpours and cloud- to-ground lightning will
accompany many of the storms.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>