Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 111841

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
241 PM EDT Tue May 11 2021

A moist stationary front will remain south of the area and maintain
rain chances over the next couple days. Dry and cool high pressure
builds in from the north by Thursday and slowly warms through the


As of 215 pm EDT: Relatively quiet across the western Carolinas
and northeast Georgia this afternoon, with a wide ribbon of high
clouds moving over the mtns and northern zones and cloud streets
over the I-85 corridor. A weak sfc trof over the mtns should drift
southeast this evening. Temps were in decent shape.

The situation is expected to go downhill later tonight as
moisture rides along and over a quasi-stationary boundary to our
south. Guidance shows an increase in mid/upper forcing late this
evening as the right entrance region of a jet streak to our north
slides overhead, while dpva associated with a dampened short wave
moves overhead. The forcing peaks in the morning hours on Wednesday,
acting on deep moisture to spread an area of light rain across most
of the forecast area. Thus, precip probs ramp up from the southwest
late tonight and max out by mid-morning with categorical across
northeast GA and Upstate SC, and likely across NC. The precip will
leave us with a cool pool across the region that will give us a
wedge-like day with high temps well below normal and more typical
of March than May. The passage of the short wave should take most
of the precip eastward during the middle part of the day, but it
appears unlikely that temps will have the time to recover much.


As of 215 PM EDT Tuesday...A shortwave trough will push into the
TN Valley Wednesday night and across the forecast area Thursday,
providing strong mid-level forcing. But there will be a lack of
moisture with the wave, and only a slight chc to low-end chc of
some showers is expected Thursday. The wave may provide a fair
amount of mid and high clouds, and with thicknesses still chilly
from the continental high sprawling over the region, temps will be
10-15 deg below normal. Could see some patchy frost in the highest
elevations, but cloud cover and lingering light winds should really
limit the potential, despite some areas getting into the 30s.

The wave will pass by quickly to our east Thursday night into
Friday, as flow remains quasi-zonal. But a flat upper trough will
linger along the East Coast. Profiles also keep some mid-level
moisture around, and could see a few showers in the NC mountains
late Thursday night into Friday, thanks to an easterly upslope
flow. But overall, it looks dry with partly to mostly cloudy skies
overnight decreasing to mostly sunny skies Friday. Temps Thursday
night will remain about 5-8 deg below normal, not quite as cold as
Wednesday night. Then rebound a couple categories over Thursday`s
highs, but still 8-10 deg below normal Friday.


As of 230 PM EDT Tuesday...A split flow pattern over the
northeastern CONUS will kick off the extended forecast period. An
area of low pressure will track off the Mid-Atlantic coast Friday
night into Sunday while heights gradually build in response to high
pressure over the eastern CONUS. Any lingering showers across the
northern NC mtns should quickly retreat Friday evening. Saturday and
Sunday should remain mostly dry across the CWA; however, isolated
thunderstorms are possible Sunday afternoon across the far northern
tier of the NC mtns. These thunderstorms would be associated with a
warm front located over the Ohio Valley remain just to the west of
NC. Lows Friday night and Saturday night will be below normal. High
temps on Saturday and Sunday will be a few degrees below normal.

Monday into Tuesday shower and thunderstorm chances increase due to
the warm front lifting north across the Ohio Valley and the Mid-
Atlantic. This front will also allow high and low temps to increase
becoming closer to normal and even perhaps a few degrees above
normal at times thanks to WAA. Models are in fairly good agreement
that Monday will trend drier while Tuesday trends a bit wetter. The
GFS currently has the precip moving in quicker and has more
widespread coverage of PoPs compared to the Canadian and ECMWF. Due
to these timing differences and in collaboration with neighboring
WFOs, I have maintained a slight chance to chance for PoPs on both
Monday and Tuesday. Monday afternoon the severe threat looks fairly
minimal as the global models show fairly minimal SBCAPE values.
Tuesday afternoon the instability looks more impressive with modest
CAPE and shear values present in all of the global models. We will
continue to monitor the progression of this warm front and its
potential impacts in the coming days.


At KCLT and elsewhere: Anticipate mainly VFR cigs today as a frontal
zone settles south of the region while another reinforcing cold
front approaches from the north. KAVL will be the main exception,
with brief IFR cigs developing in the French Broad Valley which will
be slow to scatter through mid morning. Steady NE flow early will
become variable to southwesterly through the afternoon hours, before
turning back to northeasterly tonight with the arrival of the
reinforcing front. KAVL will be the main exception on winds as well,
with steady NW flow through the period. A few low end gusts will be
briefly possible as mixing starts. Deeper moisture arrives tonight
and cigs will lower as the precipitation spreads in from the west.
Lowering VFR will become MVFR overnight, with spotty IFR possible
around daybreak depending on the rainfall intensity.

Outlook: With a stalled frontal zone near or just south of the area,
periodic low cigs/vsbys and SHRA are expected to continue Wednesday
and possibly into Thursday. This should be followed by gradual
drying late in the week and into the weekend.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     Med   77%
KGSP       High  96%     High 100%     High  85%     Med   76%
KAVL       High  92%     High  98%     High  91%     High  93%
KHKY       High 100%     High 100%     High 100%     High  80%
KGMU       High  95%     High 100%     High  90%     Med   74%
KAND       High  95%     High  95%     Med   79%     Med   79%

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:




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