Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 161055

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
655 AM EDT Wed Aug 16 2017

High pressure is expected over the next few days leading to hotter
conditions and below normal chances for convection.  Moist and
unsettled weather gradually returns late week and into the weekend.
Some drying is favored into Sunday with a return to moist conditions
to start the new work week.


As of 655 AM EDT: Models have trended toward higher condensation
pressure deficits around daybreak this morning, and widespread fog
seems unlikely unless we get a sunrise surprise. Will just keep
patchy fog wording going mainly in the mountains.

Otherwise, the southeastern ridge will become resurgent today
through tonight. Under the slowly building upper ridge, lapse rates
and afternoon sbCAPE values should remain relatively modest and the
convection-allowing models show limited coverage this afternoon and
early evening. Still feel that the best scattered shower and
thunderstorm coverage should be along the eastern slopes of the Blue
Ridge and the immediately downstream western foothills during the
mid to late afternoon hours. Max temps this afternoon should reach
the 90s in most areas east of the mountains, and heat index values
should reach 100 in the lower piedmont. Early evening convection
should wrap up quickly tonight. Expect another warm and muggy night
with min temps some 5 to 10 degrees above climo and another round of
patchy fog developing toward daybreak Thursday.


As of 300 AM EDT Wednesday:  The short term fcst period kicks off on
Thursday morning amidst shortwave ridging aloft across the extreme
southeast states thanks a broad anticyclone centered in the GOM,
while a neutral/negatively tilted trof moves through the upper
Midwest and into the mid/upper MS River Valley.  At the surface,
weak high pressure will be in control over northeast GA and the
Carolinas while a region of cyclogenesis and an associated front
moves beneath the aforementioned upper trof.  Pattern evolution
through Thursday will favor increasing moisture amidst slowly
falling heights aloft, with guidance suggesting weak lee trof
development over the Fthills/Piedmont regions.  Therefore, with
profiles being rather unstable think said lee trof could provide a
focus for convection, which is fcst to develop along the high
terrain before propagating east into the low terrain.  The fcst will
feature fairly healthy pops with likely levels highlighted over the
mtns with high chance pops elsewhere.  Said pops will lower through
the overnight as instability wains leading to a mostly dry fcst to
start off Friday.

The above mentioned cold front will approach western NC by mid/late
day Friday allowing for ample heating out ahead.  Another round of
convection looks probable along the front in the evening hours,
however with profiles on Friday actually being a bit more moist
through the column, and thus limiting lapse rates to some degree.
Timing of the fropa will be key, however at this point the guidance
doesn`t look all that excited as it pertains to convection given
that the fropa is progged after peak heating.  That said, pops on
Friday will be above climo, but generally capped in the mid/high
chance range regionwide.  Temperatures through the short term period
will be quite warm at a few degrees above normal levels with heat
indices both days approaching/exceeding the century mark, especially
south of I85.


As of 315 AM EDT Wednesday:  The medium range fcst period
initializes on Saturday morning in the wake of a weak sfc fropa,
while an upper trof is staged just to the west.  Said surface front
looks to stall out across the Midlands, northeast into east/central
NC providing a focus for convection during the afternoon hours with
some enhancement possible given falling heights and intruding
shortwave energy.  That said, for the most part OP guidance favors
near climo pops across the CWFA as drier high pressure noses in
behind the front.  Near normal pops are favored again on Sunday as
high pressure looks to dominate leading to only diurnally favored
convection, all while transitioning eastward across the northern
Appalachians over the Delmarva by Monday.

For Monday, The stationary front looks to gradually lift northward
out of the Midlands into the Upstate by early afternoon, per both
the GFS and ECMWF.  Low level RH fields in both models favor RH in
excess of 70% with profiles exhibiting modest lapse rates.
Therefore chances for convection remain elevated with fcst pops in
the mid chance range, and sky cover still around 50-60%.  The front
is progged to lift north of the area on Tuesday as the western
Atlantic ridge controls the llv flow, all while another upper trof
digs across the central CONUS.  Therefore think convection on
Tuesday will return to more of a diurnal trend with pops near
climo.  Temperatures through the period will kick off near normal
over the weekend, cooling a few degrees on Monday given the
proximity of the front and any associated sky cover and convection,
then returning to normal for Tuesday.


At CLT and Elsewhere: Sunrise fog seems a bit less likely at the TAF
sites this morning as model condensation pressure deficits have
trended higher. Will still keep a couple of hours of FEW stratus at
KAVL to hint at potential issues, but chances do seem smaller now.
Otherwise, expect scattered cumulus with heating today, and PROB30
for SHRA/TSRA mainly at KAVL and across the foothills from KGMU to
KGSP to KHKY late this afternoon. Light winds should gradually
toggle southwest through the day, perhaps taking until evening to
make the adjustment at KCLT. Profiles suggest better mountain valley
fog for late tonight.

Outlook: The transition to a more typical late summer pattern is
expected by the end of the week, continuing into early next week,
with scattered afternoon convection and morning low stratus and
patchy fog likely each day, especially in the mountain valleys and
in locations seeing appreciable rainfall.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High  94%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     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:




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