Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 302026
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
426 PM EDT SAT JUL 30 2016

.SYNOPSIS...
A subtropical high off the Atlantic coast will maintain shower and
thunderstorm chances and high temperatures above normal through the
rest of the weekend and early next week. A stationary boundary will
sag into the area next week, keeping afternoon rain chances in the
forecast.

&&

.NEAR TERM /THROUGH SUNDAY/...
2030 UTC Update: Pops and QPF were adjusted based on radar trends to
account fro a band of activity crossing Upstate SC and the southern
tier of western NC.

As of 215 PM EDT Saturday: Upper trough remains in place over the
Great Lakes, extending down the Mississippi Valley, with upper high
over the western Atlantic ridging toward the FL peninsula. We are
left in an area of weak southwest flow aloft, with a warm and moist
airmass in place. Slow-moving cold front remains draped across the
Ohio Valley, with surface high pressure dominating the Southeast but
the typical lee-side troughing over the Piedmont. Scattered showers
and thunderstorms have already developed at AFD time but with only
modest sbCAPE in place, very little upper support, and dCAPEs less
than 700 J/kg, expect mostly garden-variety thunderstorms this
afternoon with any strong to severe threat incredibly low. Low-level
lapse rates are marginally supportive of brief weak microbursts but
without the dCAPE, and with poor mid-level lapse rates, generally
expect just the typical gustiness, lightning, and locally heavy rain.

We should see another impulse moving through the flow aloft
tomorrow, much more evident in the 700mb flow as a weak shortwave
trough that will bring with it a slug of low-level moisture, and a
weak 500mb vort max (maybe "max" is a misnomer but it`s all
relative). These should help to enhance convective potential for
tomorrow, but not necessarily intensity as WAA at mid-levels will
further decrease lapse rates. The best are for convective
development will be across the mountains as usual as well as the
northern tier of the foothills and Piedmont closer to the upper
system, where sbCAPEs tomorrow are progged to be at least 500 J/kg
higher tomorrow than today.

Temperatures will continue to run a degree or so above seasonal
normals for both highs and lows. With continued afternoon mixing,
despite the plentiful low-level moisture, we should continue to
remain below below heat advisory criteria, though heat indices will
likely creep into the lower 100s across our southern zones and into
the Upper Savannah Valley.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 225 PM Saturday...the models continue to suggest we should
have a decent chance of developing mainly duirnal showers and
thunderstorms early in the week. The axis of a broad upper trof
should move across the region slowly on Monday with one or two weak
waves embedded in it. This should push a weak sfc boundary down
across the fcst area that will help to pool moisture and provide a
focus for deep convection once we heat the boundary layer. Think it
best to keep precip probability in the chance range for the time
being, but storms should be more numerous than the past several
days, so the probability might need to be bumped up with later
forecasts. Temps will remain seasonally warm, about a category above
normal, with the heat index reaching the upper 90s along and S of
I-85, but this is not unusual. The storms should move off the mtns
in the evening and then dissipate during the late evening. Tuesday
is a bit more interesting in that the new guidance, especially the
NAM, develops more in the way of precip coverage in the afternoon.
Perhaps this is because the sfc boundary remains strung out across
the region instead of being driven south of the region. Will bump
the precip chances up across the region a bit to put more of the
fcst area in the chance range. Precip chances will diminish again
with a loss of heating. Temps will be similar to Monday, so again no
heat advisory is anticipated.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 230 PM Saturday...medium range begins 12Z Wednesday with a
longwave trough moving off the East Coast and an upper ridge
building over the eastern third of the CONUS. This will temporarily
bring our CWA under the influence of northwesterly flow on Wednesday
and Thursday, allowing a train of shortwaves to make their way over
the area. The upper support coupled with the weak surface boundary
that will likely still be in place over the Carolinas will slightly
enhance our normal summertime diurnally driven convection. The
surface boundary appears to wash out on Thursday, though warm and
moist southwesterly flow (including an upslope component for the
higher terrain) will keep afternoon shower and thunderstorm chances
a bit above normal. Guidance then diverges somewhat through the end
of the period. The general trend depicted by most major models is
the development of an upper longwave trough over the eastern CONUS
next weekend, with a frontal boundary approaching the area.  Timing
and strength of these features is still quite uncertain, so precip
chances were kept near to a little above climo for next weekend.
Still...it is reassuring to see that extended guidance may be
hinting at the possibility of some increased rain chances and high
temperatures closer to normal at the very end of the period. Until
next weekend though, max and min temps will stay about a category
above average.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
At KCLT: Convection has developed across the area and VCSH with
TEMPO -TSRA from 19-23z still looks good. Added the VRB10G20KT to
the TAF to account for sub-severe microburst potential with
collapsing thunderstorms. Otherwise, VFR through the period with
mainly SCT mid-level clouds. Winds should favor SW around 5kt, with
slightly lower speeds overnight. Will likely need to introduce
PROB30 -TSRA for Sunday afternoon with the next TAF set, as best
chances are after 18z.

Elsewhere: Trends very similar to that of KCLT above, though the
only TEMPO TSRA currently is at KAVL with VCTS elsewhere. Will AMD
as necessary if/when convection gets closer to the terminals.
Introduced PROB30 TSRA starting 16z Sunday for KAVL and like KCLT
will likely need to add to other sites with next issuance. Expect
some morning MVFR fog at KHKY and KAVL. May need to add TEMPO for
potential IFR with later TAF issuances.

Outlook: Typical summertime pattern in place with afternoon TSRA
expected each day, as well as potential for early morning
restrictions especially in the mountain valleys.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
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  95%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...LEV
NEAR TERM...JAT/TDP
SHORT TERM...PM
LONG TERM...LEV
AVIATION...TDP



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