Area Forecast Discussion
Issued by NWS Greer, SC

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860
FXUS62 KGSP 261037
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
637 AM EDT THU MAY 26 2016

.SYNOPSIS...
Moist southerly flow will lead to warmer temperatures and mainly
afternoon chances of showers and thunderstorms today and Friday. A
period of cooler and wetter weather may develop late in the weekend
as Atlantic low pressure moves onto the Carolina coast.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 635 AM: mid level clouds are spreading across the area ahead
of a weak short wave. Convection has developed over E TN and is
moving toward the mountains. Have sped up the timing of precip onset
across the mountains, but kept timing across the rest of the area
nearly unchanged. The moist southwesterly flow across the area will
keep copious low level moisture in place, leading to an increase in
cumulus development today. The continued low level moisture will
lead to an increase in instability with moderate sbCAPE values
likely across the mountains, and moderate MUCAPE values possible
across much of the CWFA. With the weak forcing and the potential
moderate instability, expect much better convective coverage to
develop today. The synoptic scale and convection allowing models
agree on good coverage developing across the mountains then breaking
containment and spreading into the foothills before dissipating
across the piedmont. Have followed these trends with highest PoP
across the mountains, low end scattered PoP into the NC Foothills
and I-85 corridor of the Upstate and NE GA, with isolated coverage
elsewhere. Wind shear is forecast to remain light, but can`t rule
out some strong storms across the mountains where instability and
forcing will be greatest. Convection should taper off through the
evening with lingering clouds overnight. Highs today and lows
tonight will be around 5 degrees above normal.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 145 AM Thu: A broad upper ridge associated with the Bermuda
High will straddle the East Coast Friday morning. Guidance
hints at an area of weak convergence and moisture pooling over
the area at that time, and as a result some models (namely GFS)
feature ongoing precip thru the morning. This appears overdone,
given the indistinct nature of forcing; PoPs are more likely to
result from diurnal convection. Initially southerly low level flow
will back later in the day in response to a wave of low pressure
rounding the ridge. Model consensus is for a seasonable amount
of instability to develop by early afternoon; upslope flow may
enhance convective coverage slightly. Relatively dry profiles
and near-zero shear imply pulse storms will be the dominant mode,
with downburst winds being the main concern.

Winds continue to back into early Saturday as (sub-)tropical low
pressure approaches the SC coastline from the southeast. Subsidence
ahead of this feature is shown to bring a swath of dry air over our
CWFA during the day Saturday. Convection will be suppressed over
the majority of the area as a result, though unstable conditions
will occur to our immediate west and southeast, so low PoPs are
retained along the Tenn border and over the lower Piedmont. Saturday
night the tropical moisture will begin to advect into the area as
the low encroaches on the coast, though there is low confidence
on how fast this will occur. Increasing clouds and precip chances
will occur after midnight over the eastern half of the area.

Temps are based on a bias-corrected blend. Maxes will be a couple
degrees above climo Fri and Sat, with mins slightly above normal
Saturday morning. By Sunday morning the increased moisture and
cloudy skies will keep temps several degrees warmer over the
Piedmont.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 300 AM Thu: Confidence in this portion of the forecast
is still limited due to differences in the modeled track of
(sub-)tropical low pressure. The EC seems to have had the best
consistency over the past couple of days...bringing the low up to
shore near Myrtle Beach, then gradually taking it up to the Outer
Banks before moving it back out to sea. This results as the low
gets absorbed into a trough crossing the NE CONUS. GFS has not had
the same degree of consistency, but most runs (including latest)
have brought the low onshore and up into the Piedmont, where it
eventually dissolves. It depicts that northern trough being less
amplified and having little effect on the low. The GFS solution
would be notably wetter for our area with winds remaining easterly
to southeasterly throughout the system`s life cycle, compared to
the EC which produces a drier northerly flow since the low remains
to our east.

At this point little change has been made to PoPs, though the
updated values reflect less of a diurnal trend. They remain in
chance range at most. Even following the dissolution of the system
the two models feature lingering effects, though it appears likely
we will be under the influence of a moist southeasterly flow at
that time. Max temperatures thru the period will remain near climo,
with mins a few degrees above due to moist conditions and nocturnal
cloud cover.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VFR through most of the period, outside of
thunderstorms. Mid clouds will spread east across the area this
morning. Winds will be light S to SW. Expect another round of low
VFR Cu developing by noon but with increasing moisture probably more
coverage resulting in ceilings for the afternoon and evening. The
convection-allowing model guidance and the synoptic scale guidance
indicate scattered convection forming over the mountains and
spreading into the foothills with only isolated coverage over the
piedmont. Therefore, have retained the PROB30 at all sites but KCLT
where chance is lowest. With convection ongoing across E TN, did add
VCTS for KAVL starting at noon followed by a PROB30. Convection ends
and lower clouds scatter out through the evening. Could be some MVFR
fog developing before daybreak, with KAVL seeing the highest chance.
SW winds develop through the morning then taper off this evening.

Outlook...Mainly VFR conditions will prevail through the period, but
patchy morning fog chances continue at KAVL. Scattered afternoon
SHRA/TSRA coverage will increase on Friday, with more uncertainty
into the weekend and early next week.

Confidence Table...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       High 100%     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 schedule 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...Wimberley
NEAR TERM...RWH
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...RWH



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