Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | 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
000
FXUS62 KGSP 190012
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
812 PM EDT Fri May 18 2018

.SYNOPSIS...
The threat for numerous showers and a few thunderstorms will linger
into Saturday as a slow moving low pressure system impacts our
region. Locally heavy rainfall will remain possible until the low
departs. High temperatures will be near to just above normal and low
temperatures about ten degrees above normal.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 810 PM EDT Friday: Main update for the 00Z TAF issuance
along with minor tweaks made to temperatures to coincide with
latest trends. The Flash Flood Watch has been updated with this
forecast update as well. Macon, Rabun, Oconee and Jackson
counties are no longer included within the watch area. The rest
of the counties previously included within the watch area
remain under a Flash Flood Watch now through early Saturday
morning.

Showers and isolated thunderstorms continue to move/redevelop
across the NC mountains and northern foothills attm, with
torrential rainfall and already saturated grounds favoring
flooding issues. Elsewhere, latest radar depicts another round
of showers and thunderstorms moving into the southern portions
of the FA, gradually moving towards the I-77 corridor. Expect
this shower and thunderstorm activity to continue well
throughout the evening hours, however latest guidance continues
to not have the best handle on the evolving situation, thus
leaving confidence on coverage of activity overnight low attm.

Otherwise, a broad upper level trof continues to spin across the
South maintaining deep and moist s/ly flow into the FA. This pattern
will change little during the period, with some n/ly lift expected
by Sat afternoon. Expect less thunder chances overnight, yet still a
high PoP -shra thru the morning with a continued hydro threat across
the srn BR. Thunderstorms will once again be possible by mid-day Sat
within a persistent and high confidence synoptic pattern. Mins
overnight will be held abt 10 degrees F abv normal with widespread
low cloud cover. Maxes Sat will be right arnd normal and with high
sfc td/s it will feel rather muggy once again.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 225 PM EDT Friday: Subtropical anticyclone remains anchored
off the Southeast Atlantic coast throughout the period. Another
upper low, although weaker and not well defined, will move out of
the Gulf of Mexico into the Gulf coast states by Monday. These
features keep a moist south to southwest low level flow across the
area each day. The good news is the deep tropical moisture fetch
will not return during this period. However, instability will
increase each day, along with decent upper divergence, keeping the
threat of mainly diurnal convection in place. Greatest coverage
continues to be across the mountains both days with high end
scattered coverage elsewhere. Shear is relatively weak both days,
but surface delta theta-e values increase with steadily drying mid
levels. This leads to an increasing threat of severe thunderstorms
each day, but these should remain isolated as overall DCAPE values
remain on the low side. Heavy rain is possible but the threat is not
as widespread as in previous days. Still, the wet antecedent
conditions could make flooding possible with lower rainfall amounts.
Highs will be nearly steady around 5 degrees above normal. Lows will
be nearly steady as well but around 10 degrees above normal.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 200 PM EDT Friday: Still little airmass change expected as the
medium range begins Monday night. Models are generally plagued by
disagreement in the finer details of the forecast, which
unfortunately make all the difference in a nebulous pattern like the
present one. A Bermuda high will remain off the east coast in the
Atlantic (welcome to summertime), with the southeast on the northern
periphery of an upper subtropical high. Some type of surface
stationary boundary will likely be laid over the Carolinas through
much of the next work week with little progression out of the area
expected. The GFS does spin up an upper/surface low over the
northern Gulf and swing it up towards our area Wednesday, but that
is likely an artifact of a known convective feedback problem in the
GFS (the parallel FV3 core has it too while the low is absent on all
other global models, suggesting this is a GFS model physics issue).
I`ve therefore favored the ECMWF through much of the medium range.

As far as sensible weather, the Bermuda high will induce weak
southerly flow over the area, though it is not as persistent our
stout as it has been over the past week. PWATs will remain elevated,
but in the absence of much large-scale forcing, a mostly diurnal
pattern favoring afternoon showers and thunderstorms will persist
through next week. Shower and thunderstorm coverage should be
decreased from this week, and chances of any flooding or severe
storms do not stand out any particular day next week at the moment.
The pattern we will enter into next week looks distinctly summer-
ish, as a matter of fact, just with a bit more moisture than usual
to work with. Max temperatures will increase a little to just above
average, with lows remaining about 10 degrees above average.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: A mixture of VFR/MVFR will continue across
the area tonight, deteriorating to MVFR/IFR overnight, as showers
and isolated thunderstorms continue to propagate portions of the
area. Between pockets of heavier downpours along with areas of low
cigs and reduced visibilities (heavy rain and/or areas of fog), a
mixture of different flight restrictions is expected. On Saturday,
expect improvement to VFR as another round of VCSH/VCTS is expected
beginning as early as late morning. Southeast winds 5 to 10 kts will
persist.

Outlook: Unsettled weather will continue into the weekend with
isolated to scattered SHRA/TSRA throughout the day/night periods and
deteriorating restrictions at times.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High  83%     High  91%     High  91%     High  94%
KGSP       High  88%     High  83%     High  81%     High  95%
KAVL       Med   76%     High  85%     High  89%     High 100%
KHKY       Med   75%     High  92%     Med   77%     High  95%
KGMU       High  91%     High  88%     High  85%     High  96%
KAND       High  88%     High  85%     High  93%     High  98%

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...Carroll
NEAR TERM...SBK/SGL
SHORT TERM...RWH
LONG TERM...Carroll
AVIATION...SGL


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