Severe Thunderstorm Warning 71, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
223 PM EDT Thu Jun 20 2019

.SYNOPSIS...
Thunderstorm activity will push east of the area late this afternoon
as a cold front passes through. The passage of the front should give
us a break on Friday as high pressure briefly sets up, but showers
and thunderstorms will return over the weekend into next week.
Temperatures and humidity will be typical of summertime for the next
week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 220 pm EDT: A Severe Thunderstorm Watch remains in effect for
areas just east of the southern Appalachians through 10 pm EDT.

The upper support is starting to arrive from the west, but surface-
based instability has been modest due to the morning convective
debris and then the invading altocumulus from the west early this
afternoon. However, the latest LAPS surface-based CAPE analysis does
show 1500 to 2000 J/kg in spots east of the mountains. Expect
coverage to steadily increase from the west and strenghthen as a
strong upper vorticity lobe and upper jetlet divergence cross the
region ahead of the approaching trough axis through 21Z. Another
trailing vort maximum in the main trough axis will cross the
northern tier through 00Z, but winds veer more westerly and dry air
wraps in at mid-levels to yield lesser coverage and weaker showers
and thunderstorms with that second wave. Sfc to 6 km bulk shear will
easily reach 40 to 45 kt with the lead wave and damaging winds will
be the primary threat. Cannot rule out an isolated tornado with any
briefly backed flow east of the lee surface trough. We will probably
be able to cancel the Watch from the west earlier than 10 pm as the
stronger convection moves through by early evening.

Anticipate deeper layer northwest setting up tonight through Friday
as modest height rises develop from the west. 850 mb flow will
strengthen this evening and overnight, with 40 kt during the peak of
the cold advection behind the passing trough. Anticipate sub-
advisory gusts, with the highest values along the northern Blue
Ridge mountains. Any lingering northwest flow moisture will dry up
quickly through Friday morning. Continued downsloping flow will aid
warming on Friday, with some lower 90s expected east of the
mountains. Any MCS activity developing over the midwest Friday
afternoon should remain well northwest of the southern Appalachians
through sundown.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 200 PM EDT Thursday: A mid level trough across the
intermountain west will cause ridging to develop across the middle
part of the country this weekend. One result of this ridging will be
for thunderstorm complexes to develop on the north side of the ridge
and drop southeast into our forecast area. This will begin Friday
night and continue through the weekend. One complication of this
pattern, which will impact all forecast elements, is that there will
likely be outflow boundaries and convective debris with these
complexes which will regulate temperatures. The resulting
differential heating each day will determine the location of where
storms will develop each day. A few of the storms could become
severe each afternoon and evening.

Overall the temperatures are expected to be near normal but some
locations may need adjustment down in the near term once the
convective patterns are established.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 200 PM EDT Thursday: The mid level pattern will change early
next week as the ridge axis moves off to the east and the trough
mentioned in the short term discussion moves across the Great Lakes
states. A weakening cold front will push toward the area providing
the focus for shower and thunderstorm activity Monday and Tuesday.
The front will not make it through the area so the pattern will
become more diurnal and typical by the middle of next week.

Temperatures through the extended period look to be near to slightly
above normal.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Convection continues to fire this afternoon
along the I-40 corridor, mainly east of KHKY and north of KCLT.
Anticipate the activity filling in from the southwest mid to late
afternoon as the upper support moves into the region. Will maintain
TEMPO for thunder at KCLT and KAND, with lesser VCTS chances at the
other sites. Will retain prevailing SW gusts with mixing, NW at
KAVL, and also TEMPO VRB gusts to 30 kt with TEMPO thunderstorms.
The activity should sweep east of the area quickly around 00Z to end
the thunderstorm threat. Mainly high debris clouds will be leftover
tonight into Friday under deeper layer northwest flow. NW gusts will
persist at KAVL through the period, but with winds decoupling east
of the mountains. Wind gusts may return with mixing from KGSP to
KCLT northward late Friday morning.

Outlook: Some drying is expected on Friday. Saturday remains fairly
uncertain as a frontal boundary lingers in the area and additional
showers and thunderstorms may move southeast into the region along
the front. A more diurnal pattern to any isolated to scattered
showers and thunderstorms is then expected Sunday and Monday. Expect
mainly daybreak restrictions each day, aside from any thunderstorms.

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  97%     High  99%
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...SW
NEAR TERM...HG
SHORT TERM...SW
LONG TERM...SW
AVIATION...HG

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