Area Forecast Discussion
Issued by NWS Greer, SC

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749
FXUS62 KGSP 201737
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
137 PM EDT WED JUL 20 2016

.SYNOPSIS...
A typical Bermuda high pressure pattern will set up across the
region through the end of the week, resulting in typical midsummer
conditions. Hot high pressure will strengthen this weekend, then a
weak cold front will approach from the northwest early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 130 PM Wednesday...we await for cells to appear on radar over
the higher terrain where satellite imagery shows enhanced cu.
Nothing in the recent CAM guidance to suggest that our fcst is out
of line, so few changes were made to the fcst.

The elongated easterly-stretching ridge from upper high over the
Plains will pull back to day from our area as the flow aloft
transitions to more NNW rather than NW, with continued weak
diffluence. Should still see a bit of lee troughing across eastern
zones, but with mesohigh in place as usual across the mountains.
Should see a fairly diurnal, maybe slightly less than diurnal trend
to convection today with highest chances over the mountains, and not
much over the Piedmont, with most precipitation dissipating after
00z. SPC just has general thunder over the area and profiles seem to
line up with this thinking, especially as afternoon mixing mixes out
some of the instability. As usual, can`t rule out an isolated strong
storm or two, but without an upper impulse moving through to provide
some lift, should be more just terrain-induced. PW values remain
high and so will have to watch heavy rainfall potential. High
temperatures will be pretty close to those yesterday.

For tonight, a little more uncertain when it comes to precip
potential. All of the models have the remnants of yesterday
evening`s convective complex working its way southeast around the
northern periphery of the upper high and toward the TN Valley late
this evening. The GFS and NAM are a little more aggressive with
taking a piece of this energy and redeveloping it across the Upstate
(in the GFS) or Midlands (NAM) of SC toward the very end of the
period. ECMWF remains dry. WPC used a blend of the NAM/GFS/CMC and
does have some precip advertised across our southern zones after
midnight tonight. For now, will continue to advertise a dry forecast
per the ECMWF, but the day shift will have to take a close look at
this and adjust if necessary. For overnight lows, very little change
from what we`ll be seeing this morning.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 245 AM Wednesday...The gargantuan upper level anticyclone will
continue to dominate the central CONUS Thursday, then begin to break
down slightly and retrograde more toward the west on Friday. The
models continue to be all over the place with individual impulses
riding around the periphery of the high. Nothing substantial appears
to cross our area during the short term. So the expected forecast is
for typical midsummer weather with diurnally driven pulse
convection, starting in the Mountains and then favoring the Piedmont
in the evening. It is interesting how all the operational models
agree on convection converging on the Upstate Thursday evening. For
now will go with chc PoPs for that. PoPs on Friday will be around
climo, if not more isolated. Temps will be about a category above
normal Thursday and another category or two warmer on Friday, as the
subtropical ridge strengthens over the Southeast.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 315 AM Wednesday...The broad upper ridge will continue to
expand into the Southeast states Saturday and Sunday, then a trough
within the northern stream will try to make some inroads across the
Great Lakes and Ohio Valley Monday and Tuesday. The 00z GFS and
ECMWF have perhaps backed off the high temps slightly for the
weekend. But still expect upper 90s to around 100 both days. Heat
indices will flirt with 105 across the Piedmont both days, with
Sunday looking to have have the highest values. A cold front will
approach form the NW on Monday, and may keep dewpts even more
elevated while temps remain in the mid 90s. So Monday`s forecast
heat indices have been trending up. Will continue to mention
excessive heat possible in the HWO. As for PoPs, they should be on
an increasing trend, especially Monday and Tuesday, as the front
approaches and the upper ridge weakens. The model Superblend has
likely PoPs in the mountains both days, but I will cap it at
high-end CHC for now.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
At KCLT...VFR expected thru the period, provided that an isolated
shower or storm does not form at the site unexpectedly. Cloud base
for few cu should lift to 050 or greater by the start of the period.
Wind should be light from the NE through the afternoon. Think chance
of precip restriction is too low to mention. Wind should come around
to something S of E this evening, perhaps initially on an outflow
boundary. Models retain quite a bit of low/mid level moisture
overnight and Thursday morning, so some cloud cover is expected
mainly at mid levels.

Elsewhere...kind of tricky. The model guidance seems to be latching
onto some remnant feature, perhaps from convection over the Midwest,
to redevelop and keep some convective precip going overnight mainly
in the Savannah R basin. The GFS in particular is keen on keeping
something in that area thru the overnight and then redeveloping with
early convective initiation Thursday morning. This would be
discounted if not for agreement with several of the convection
allowing models. So, we view this with caution. The biggest threat
would be to KAND. This could at a minimum develop and keep a low
cloud deck over the area through Thursday morning. Will start a
trend in that direction with a VCSH at KAND overnight and advise the
next shift to be on the lookout for greater potential for low
cloud/vis restrictions. An earlier convective initiation suggests
introducing a PROB30 at KAVL in the late morning Thursday. The rest
of the TAFs keep the precip out thru the end of the period. Winds
will come around to light SE or S overnight.

Outlook: Expect to revert to fairly typical midsummer weather with
afternoon showers and thunderstorms during the latter part of the
week. Morning fog and low stratus will be possible each day in the
mountain valleys and also in locations that received heavy rainfall
in the preceding afternoon/evening.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High  83%
KGSP       High 100%     High 100%     High 100%     Med   66%
KAVL       High 100%     High 100%     High 100%     Low   31%
KHKY       High 100%     High 100%     High 100%     Med   66%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     Med   66%

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



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