Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 240246
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1046 PM EDT Sun Jul 23 2017

.SYNOPSIS...
A cold front will become stationary from west to east across our
region through the middle of the week then dissipate.  This should
result in a little cooler temperature and better chances for rain
over the next few days.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 1030 PM EDT Sunday: Well, convection is firing again
across the Upstate, and with all these boundaries all over the
place, I suppose it`s no wonder. Additionally, we`re looking at
convection heading towards the mountains from KY/TN/VA. With all
this, have increased pops through the overnight hours but sort of
hard to tell how we should adjust trends thereafter, as CAM guidance
seems to want to keep it going through daybreak. Have adjusted
temperatures down a bit as well especially in the mountains and
foothills where obs are running a little lower than forecast.

Otherwise, mountain valley fog, some dense, is expected again and
locations outside of the mountains that receive rainfall may see
some as well. Lows will again be above normal but not quite as warm
as last night.

Convection redevelops Monday as outflow boundaries from the
overnight MCS move across the area. Coverage will be better along
and south of the I-85 corridor where the timing of the boundary
movement will coincide with the higher instability. North of the
corridor instability will be much less leading to only isolated
coverage at best. DCAPE and sfc delta theta-E values while still on
the high side, will not be as high as Sunday. Instability will reach
moderate levels but just barely. Therefore, the chance of severe
storms will be less but not non-existent. Highs will be in the lower
90s outside of the mountain, and while still humid, heat index
values should remain below 100.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 200 PM Sunday: A weak and nearly stationary cold front
will remain over central GA and SC Monday night into Tuesday,
immediately south of the CWFA. Aloft, we will remain somewhat
under the influence of the northeast CONUS trough, though
without significant embedded vorticity in play early in the
period. More abundant moisture will be present over the south,
near the front, which could increase cloud cover. But otherwise it
appears conditions will be close to climatology, with seasonably
modest instability and weak shear producing a small pulse severe
threat. Partial thicknesses change little from Monday, so max
temps should be similar.

Tuesday night, high pressure will shift into New England in the
wake of the upper trough. A weak upper low is shown to cut off
and remain over the Carolina coast, and allows enough vorticity
to persist over the area that isolated t-storms still could fire
overnight across mainly the Piedmont. The eastward push of the high
will bring cooler air south into the area, which virtually all
guidance indicates will knock max temps down to a couple degrees
below normal, in conjunction with increased cloud cover. Nonetheless
consensus SBCAPE values remain fairly large given still-elevated
sfc dewpoints and good lapse rates afforded by the upper low. PoPs
peak above climo and pulse threats return once again.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 145 PM Sunday: The medium range begins Wednesday evening with
a weak closed off 500mb low over the Carolinas and Georgia. As the
next northern stream shortwave crosses the Great Lakes on Thursday,
it kicks this weak low off to the east with the 500mb trough digging
over the East through the weekend. As the Great Lakes shortwave
moves to far eastern Canada, the associated cold front moves slowly
southeast. This front should be nearing the Ohio River early Friday.
As the front approaches from the north, frontal associated
convection will increase first across areas along and north of I-40
Friday afternoon and then spread across much of the rest of the area
Friday evening. The front becomes stationary west to east across our
region through the weekend. The eventual location of the axis of the
trough next weekend varies among the models. This axis location will
have significant influence on our weather. Also, mesoscale
convective systems are expected to develop near the Rockies or
northern Plains states and track southeast in the northwest 500mb
flow toward our region of the nation. Therefore, our weather will
remain unsettled through the weekend. Temperatures will be near
normal.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Convection has redeveloped across the
Piedmont, and an area of IFR to low MVFR cigs is lifting north
across the CLT area. Will add a TEMPO to the 03z AMD to cover this,
and will also add VCSH to the prevailing. Otherwise, guidance is
pointing to restrictions developing overnight at KAVL, and have
TEMPOed MVFR to IFR conditions. Also introduced brief MVFR fog at
KHKY. Cannot rule out MVFR fog at other sites given the convection
this afternoon, but for now will leave it out. Expect yet another
round of convection to develop tomorrow afternoon, with best chances
across the Upstate and KCLT. Winds generally SW through the period 5-
10kt, except NW up-valley winds at KAVL.

Outlook: Slowly increasing chances of convection expected through
the week ahead of a series of weakening cold fronts. Overnight
restrictions will continue in the mountain valleys with chance
increasing elsewhere.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High  97%     High 100%     High 100%
KGSP       High 100%     High  97%     High 100%     High 100%
KAVL       High  95%     High  88%     High 100%     High 100%
KHKY       High  98%     High  87%     High 100%     High 100%
KGMU       High 100%     High  97%     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...DEO
NEAR TERM...RWH/TDP
SHORT TERM...Wimberley
LONG TERM...DEO
AVIATION...TDP


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