Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 152051

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
451 PM EDT Sat Jul 15 2017

Hot and humid conditions will persist through the weekend, with
scattered to numerous afternoon and evening thunderstorms each day.
A cold front will move into the region from the northwest and stall
near the area through Sunday. Another cold front will approach on
Monday and move southeast of the area on Tuesday, with drier and
warmer conditions arriving by the middle of next week.


As of 440 PM EDT: The center of the CWFA has a nice cold pool
developing from the widespread convection. The leading edges of this
cold pool are where the tallest storms continue to fire. At this
pace, pretty much the entire forecast area should be worked over by
around sunset. I updated the PoPs to reflect latest radar trends and
the latest CAM PoP guidance. Temps were also adjusted.

As of 200 PM EDT Saturday: The weak cold front has generally moved
south of the area, as evidenced by WNW winds across most of the
Piedmont, but moisture associated with the upper trough will
continue to move across the area with high PW values near 2" and a
potent little vort max swinging through. Deep layer shear isn`t
impressive, and while we do have some steering flow, convective
development continues  upstream of current convection, leading to
training storms and a heavy rain threat (with associated Slight Risk
of Excessive Rain from WPC). We remain in Marginal Risk for the SPC
outlook with a low-end wind and hail threat (with slightly improved
lapse rates aloft and some area for hail growth). Despite the
proximity of the front, dCAPEs are actually fairly low, generally
<700J/kg across the area, so storms might not be able to get as
intense as quickly as they did yesterday...which also leads one to
believe this might evolve into more of a heavy rain threat. Basin-
average QPFs are not that all impressive so flash flooding would be
localized, so do not really feel a Flash Flood Watch is warranted.

Convection should wane overnight, but should pick up at least across
southern zones on Sunday. Some of the hires models want to develop
some showery activity across the northern tier as well so have kept
pops a little higher, but these may need to be pulled back down with
later forecasts. Temperatures will be improving through the period,
with highs today near seasonal normals, lows tonight just slightly
above and highs tomorrow actually a couple of degrees below.


As of 130 PM EDT Saturday: A shortwave embedded in upper longwave
troughing will cross the area Sunday night as a surface front
settles over the forecast area. The front will wash out on Monday as
heights aloft fall and another potent shortwave rounds the trough
base, so widespread showers and thunderstorms are anticipated once
again on Monday. Another front will descend from the northwest on
Monday night and will stall near the forecast area Tuesday,
providing a focus for enhanced diurnal convection in the afternoon.
Mid-level dry air makes an entrance Monday and Tuesday, and with
respectable instability both days, some type of wet microburst
threat is possible. Temperatures will be near climo.


As of 100 PM EDT Saturday: The medium range begins Tuesday night
immediately post-frontal passage with a few lingering showers and
thunderstorms. Upper troughing lifts by Wednesday, though there is
some model disagreement in just how far the front is able to
progress as it washes out on Wednesday. Strong upper ridging builds
over the central Plains on Wednesday to exert some influence on the
southeast, though, so maximum temperatures were increased and
"silent 10" pops remain. The extent to which drier air will be able
to work in as the ridge continues to build Thursday and Friday is
also uncertain, but enough moisture lingers in the global model
solutions that slight chance pops were maintained both afternoons. A
back door front dips down from the northeast as upper heights fall
again on Saturday, bringing pops close to climo back into the
forecast. Maximum and minimum temperatures during the middle and end
of next week will be above climo through the period, though the
extent is uncertain due to model inconsistencies in handling the
sprawling high over the central Plains.


At KCLT and Elsewhere: Convection developing and becoming more
widespread across the area, though still fairly sparse across most
of the Piedmont. Have started all TAFs but KAND with VCTS (KAND at
19z) but with TEMPO TSRA and VRB gusty winds. As the front sags
south, convection should diminish 00-03z or so. Expect another round
of restrictions, probably LIFR, at KAVL, and have brough in some VFR
fog at KHKY, but would not be surprised if other TAFs have morning
fog restrictions as well. With the front stalling across southern
areas, should see an increase in convection again Sunday late
morning, and have introduced PROB30s to account for this. Winds
starting out W to WNW at TAF time, should veer around clockwise to
N/NE/ENE through the end of the period.

Outlook: Scattered to numerous afternoon and evening thunderstorms
are expected through Monday across the area, with higher coverage in
the mountains. Morning fog development can be expected in the
mountain valleys and in areas that receive rainfall the previous

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  94%     Med   70%     High  98%
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:




SHORT TERM...Carroll
LONG TERM...Carroll
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