Area Forecast Discussion
Issued by NWS Greer, SC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KGSP 102331

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
731 PM EDT Mon Aug 10 2020

Daily showers and thunderstorms will steadily become more numerous
as the week progresses.  High temperatures of a couple degrees above
normal early in the week will become near to below normal by the end
of the week under considerable cloud cover.


As of 730 PM: Convection has diminished greatly early this evening
with only an isolated shower expected before midnight. The CAM
guidance still shows an upstream MCS overnight; however, they show
it dropping more southward across KY and TN and dissipating before
reaching our CWFA. A few showers may still make it into the
mountains toward morning, so kept isolated showers there, but for
now, it looks like the potential for any storms is minimal at best.
Areas of fog/stratus may form in the wake of any heavy rain that
falls this afternoon, especially in the mtn valleys.

Confidence is limited in tomorrow morning`s forecast by the
possibility of the late overnight activity. However, even the
guidance sources that show such activity do show subsequent
destabilization, and a well-defined shortwave approaching the
area in the aftn suggests better than average coverage once
again. Profiles are fairly similar, still with seasonably weak
shear and modest lapse rates. Heavy rain likely will remain the
main concern.


As of 234 PM Monday: An unsettled weather pattern is expected
through the short term forecast period as a cold front approaches
the area from the NW (progged to stall and remain outside the FA)
with a slightly weakening subtropical ridge off to the west and
broad upper troughing over the east coast. As moisture continues to
infiltrate in across the area, guidance continues to prog PWATs
nearing 2 inches on Wednesday and just above 2 inches into Thursday.
In addition to the very moist air mass, it will be an unstable one
as well as fcst soundings suggest decent available instability. Weak
embedded shortwaves moving overhead throughout the period will aid
in diurnal scattered to numerous (at times) showers and
thunderstorms throughout the period. While heavy rainfall/localized
flooding will be the primary threat, with little storm motion
anticipated, a few strong to severe thunderstorms will be possible
as well with gusty winds and even a few microbursts. PoPs do
decrease during the overnight hours, but lingering activity will
still be possible. Max temps on Wednesday will climb a few degrees
above normal while falling just a few degrees shy of normal on
Thursday. Min temps will remain above normal.


As of 230 pm Monday: A persistent subtropical ridge will remain
stagnant over much of the eastern CONUS during the beginning portion
of the medium range. Indications from model guidance show the ridge
losing its grip by the weekend as upper troughing begins to sag
lower heights from the north-central CONUS to the East Coast. The
GFS and ECMWF are in agreement of a potential pattern change over
the weekend, but both bring different elements to the table. The
ECMWF has a weak embedded low that develops from the Midwest and
into OH Valley, while digging an upper low across the Canadian
Provinces and into the Upper Great Lakes from the beginning to the
end of the extended period. On the other hand, the GFS doesn`t have
any support for a developing embedded low and keeps the same upper
low well north of the Upper Great Lakes, towards the Hudson Bay.
Both models produce an upper trough type of synoptic pattern over
the eastern CONUS late in the weekend and into the early part of
next week, but the ECMWF leans towards a more potent upper trough
than the GFS. With a low-level southwesterly flow in the area Friday
and Saturday, shower and thunderstorm chances will be highest on
these two days. Most of the activity will be diurnally driven, but
model guidance spit out a few pieces of shortwave energy during this
time frame and should allow for some of the precipitation to linger
past sunset. PWAT values will be =>2.00" outside the mountains and
could introduce a possible excessive rainfall event, especially in
areas that receive a few rounds of shower and thunderstorms. As we
head into Sunday, slightly drier air moves in as a more westerly
component builds in aloft over the region and should bring an
overall downtick in activity. Expect anything that does develop to
mainly stay within the diurnal cycle and summer-like in nature.
Looking forward into the early part of next week, the upper trough
should remain intact over the East Coast and conditions won`t change
much from Sunday. Temperatures should be at or slightly below climo
for much of the medium range due to more than usual cloud cover.


At KCLT and Elsewhere: Convection has diminished greatly with only
minor effects at the terminals this evening, mainly from lingering
low VFR and variable winds from outflow boundaries. Nocturnal
fog/stratus is likely to result in IFR for the mountain valleys
tonight. Can`t rule out fog and/or stratus at the other sites. Most
likely at KHKY/KAND, so have it there. Possible elsewhere but chance
too low to include for now. There guidance has backed off on the MCS
potential approaching the mountains late tonight. Therefore, have
removed any TAF mention. Have PROB30 for typical diurnal convection
all sites. Outflow boundaries are making wind tricky this evening.
Have gone with current conditions then light and variable overnight.
No strong consensus on wind Tuesday, so went light and variable for
all but KCLT and KAVL where NW wind prevails.

Outlook: Above average coverage of diurnal convection is expected
thru the end of the work week. Morning fog/low stratus restrictions
will be possible each morning, especially over the usual mountain

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  83%     High 100%     High 100%
KHKY       High 100%     High 100%     Med   62%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  83%     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:




AVIATION...RWH is the U.S. government's official web portal to all federal, state and local government web resources and services.