Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 291514

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1114 AM EDT Thu Jun 29 2017

Moisture will move north from the Gulf beginning today, with an
upper disturbance bringing widespread showers and thunderstorms for
Friday. Summer heat will return through the weekend, as well as a
daily chance of afternoon and evening showers and thunderstorms
through the Independence Day holiday.


As of 11am EDT Thursday: Radar is currently clear, but showers are
expected to increase initially over northeast GA and spreading
eastward this afternoon.  BL moisture continues to improve on
southerly winds and a weak shortwave is approaching from the west.
As shortwave passes over the area, associated forcing will generate
showers through Friday.  Activity is anticipated to be primarily
over the western half of the CWA today, spreading to all areas on
Friday.  With improving moisture, some thunderstorms are expected
this afternoon and Friday afternoon, though with weak wind shear and
still limited instability, there is not a significant severe threat
at this time.  Instability improves slightly on Friday, and improves
more on Saturday.

Rainfall amounts for the entire Thursday through Saturday period are
around a half inch in eastern areas to an inch and a half in areas to
the west.

Extensive cloud cover and rain on Friday will lead to seasonally
cool high temperatures with upper 70s to low 80s expected Friday


As of 230 AM EDT Thursday: Slug of moisture associated with a potent
shortwave lifting across the Southeast will be pushing into the area
at the start of the short term period. Bermuda high will continue
the warm moist southerly surface fetch, and diffluent flow aloft
ahead of the incoming shortwave will add to synoptic lift with
increasing PVA as well as isentropic and orographic upglide into the
Southern Appalachians. A mesohigh that is progged to form along the
Blue Ridge will cause winds across the Upstate and the Upper
Savannah Valley to back somewhat, resulting in an enhanced area of
low-level convergence as well. This will combine with deep-layer
moisture with PWs upwards of 2". On the flip side, because of the
widespread cloud cover, temperatures will be held a good 10 degrees
below seasonal normals (and definitely a cooling trend from previous
forecasts), and thus instability will be very lacking, with sbCAPEs
progged generally below 500 J/kg. Despite the approaching upper
shortwave, deep-layer shear is practically nonexistent with really
not much flow aloft (maybe 30kt at "jet" level...though there`s no
jet to speak of). All this points to at least a marginal heavy rain
concern. Latest WPC, GFS, and SREF QPF all point to the NE GA/SW NC
upslope areas as being the bullseye with 2-3" during the morning and
early afternoon Friday. 12z ECMWF is a tad farther south with this
max, as is the NAM, but given the pattern and upslope flow am
inclined to lean toward the former camp. However, this week has been
dry, and soils have dried out in kind. For now have no plans to
issue a Flash Flood Watch but QPF trends will need to be monitored

This shortwave passes by Friday night, with a bit of a lull in
activity, but then the longwave trough axis approaches on Saturday,
dragging a front through the Ohio Valley. The southern edge of the
front is really weak however, and looks like it gets torn up by the
mountains, so pops aren`t quite as high as we had been carrying, but
still higher than climo. However, on Saturday we`ll have instability
added to the mix as well (over 3000 J/kg progged in the Upstate),
and with some dry air aloft able to be entrained plus a decently
mixed surface layer, severe pulse thunderstorms would be an
increasing threat, with typical wind damage the main concern. Max
temps Saturday 5-7 degrees warmer than on Friday, but still several
degrees below seasonal norms. And of course, with increasing surface
moisture, lows will creep back up to near normal for Friday night
and a few degrees above Saturday night.


As of 300 AM EDT Thursday: Longwave trough will be pushing toward
the Appalachian, with the very weak front stretching down the
Eastern Seaboard at the start of the extended period. The surface
trough will hang around as we begin the holiday work week, but
generally Sunday and Monday should see a lull in convective activity
with below-climo pops but a return to normal temperatures.

By Independence Day, the longwave trough axis will remain over the
East Coast, but will lift further NE as upper high builds in over
the eastern Gulf/FL/W Atlantic. A shortwave will push out of the
Rockies, with the disturbance working its way down the MO River
Valley during the day. Pops will ramp back up a tad, closer to climo
briefly during the afternoon, but all in all not a bad night for
fireworks, with again near normal temperatures, and convective
activity waning toward 00z. Convective activity will pick up again
Wednesday afternoon and evening as the disturbance inches closer,
but still maybe just a hair above climo in the mountains. Overall a
fairly seasonal end to the period for all elements but low


At KCLT and Elsewhere: VFR conditions expected thru the first part
of the 12z taf period with visby and/or cig restrictions carried
at all sites by early tomorrow. As sfc high pressure drifts farther
offshore later this morning and deeper moisture continues to work
in from the SW, we should see a gradual increase in VFR cloud coverage
over KGSP, KGMU, and KAND. Otherwise, as an upper wave approaches
the region from the west later today, moisture will increase further
leading to low VFR cigs at KAND and possibly TSRA moving in by 20z
or so. Thunder potential should diminish there after 00z or so as
instability wanes. The other sites start carrying PROB30s for SHRA
a bit later with KCLT and KHKY being the latest. Winds should remain
SLY and pick up in speed to the 05 to 10kt range by the afternoon.

Outlook: Increasing moisture and instability is expected to result
in considerable coverage of mainly PM showers and thunderstorms Fri
and Sat and could cause flight restrictions. Otherwise, typical early
summertime conditions are expected through the weekend.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High 100%     High 100%     High 100%     High  82%
KGSP       High 100%     High 100%     High  90%     High  88%
KAVL       High 100%     High 100%     High  91%     High  81%
KHKY       High 100%     High 100%     High 100%     High  86%
KGMU       High 100%     High 100%     High  81%     High  92%
KAND       High  98%     High 100%     Med   63%     Med   64%

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:




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