Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 242215

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
615 PM EDT Tue Apr 24 2018

A slowly moving low pressure system will exit our region by
late tonight. The atmosphere will dry briefly Wednesday before
another moist area of low pressure crosses the region Thursday
through early Saturday. High pressure builds across our area by the
end of the weekend.


As of 6pm EST Tuesday:  Showers continue this evening with some
lightning primarily over eastern parts of the CWA.  Short-term
guidance has a decline in shower activity after 8pm, with residual
showers moving out of the area to the northeast.

Overall coverage of shower activity is expected to gradually
diminish into the evening, as upper low continues to wobble toward
the Southern Appalachians, allowing the low level flow to continue
to weaken while shifting to more of a downslope regime.

The surface low will move east of the area tonight, ahead of the
upper low which is forecast to move across western NC overnight. The
result will be shunting of the deeper moisture to our east and north
as the low level flow turns NW/downslope. Precip probabilities
should therefore become increasingly confined to light shower
chances along the TN border, which will persist into Wed, while
skies should begin clearing east of the mtns late tonight through
the morning. Tonight`s min temps should be a category or two above
climo in most areas, while highs tomorrow are forecast to be close
to normal.


As of 220 PM EDT Tuesday: the short term fcst picks up at 00z on
Thursday with a brief flattening of the upper pattern before another
upper trof digs down across Southern Arkansas. The trof axis is
expected to lift up and over the CWFA late Thurs into early Fri as
another trof dives down the backside of the broader upper trof.
This second trof axis is not expected to reach the fcst area until
early Sat, which is just beyond the short term period. At the sfc,
the large low that has been impacting our region will finally lift
northward and over New England. In the low`s wake, weak high pressure
will briefly move over the area from the northwest. The high will be
short-lived as another low develops to our west and approaches the
fcst area Thurs afternoon. The operational models are now in much
better agreement with the timing and placement of this low. It is
expected to move over the CWFA late Thurs/early Fri and lift north
of the area late Friday. As for the sensible fcst, PoPs were increased
for the later half of Thurs as the deeper moisture associated with
the low overspreads the CWFA. They remain high thru early Fri morning
and then taper off during the rest of the day. Some sfc-based instability
is present Thurs afternoon/evening, especially over our southern and
eastern zones, so isolated to scattered thunder is included over those
areas. High temps will be about a category below normal for Thurs and
near normal for Fri. Lows are expected to remain a few degrees above
climatology both days.


As of 230 PM Tuesday: The extended forecast starts at 00z Saturday
with yet another potent shortwave trough rounding the base of the
mean longwave trough over the Southeast states. The medium range
guidance is still not in good agreement on the details of this wave.
The 12z EC still is the further south and least phased of the
deterministic models. It takes the wave all way to the FL Panhandle.
This results in a relatively dry soln. The 12z GFS still on the
wetter side of guidance, keeping showery wx for the area on Saturday
with the shortwave tracking right thru the Carolinas. For now, the
WPC preference is toward the EC soln, and results in only SLGT CHC
PoPs for Saturday. Temps will be near normal.

From Sunday onward, conditions look dry with temps warming above
normal for the start of next week. The eastern trough should finally
start to shift east and an upper ridge will build in from the west.
By next Tuesday, the models are in decent agreement on a fairly
amplified western trough and eastern ridge pattern across the
country. Sfc high pressure will dominate our weather for Monday and


At KCLT and elsewhere: Scattered to numerous showers continue to
fire this afternoon along and north of a surface boundary extending
across northern SC, with activity primarily concentrated across the
NC foothills in response to a SE upslope flow. An area of weak
instability has developed in the vicinity and especially south of
the boundary, and the intensity of showers has been gradually
increasing over the pass hour or so in these areas. Would expect at
least a few of these to develop into TS, with the best chance for TS
existing at KAND and KCLT, where tempos for -TSRA are carried for a
while this afternoon into the evening. Otherwise, IFR to lMVFR
clouds will persist north of the boundary through much of the
afternoon, although we do expect most sites in these areas to lift
above the IFR level by mid-afternoon. As the flow begins to turn
around to more of a downslope regime, cigs may improve to VFR (or
even scatter by late evening), although ample low level moisture
could allow stratus and/or fog to fill back in overnight, but
overall confidence in flt conditions is fairly low tomorrow morning.
generally E/NE winds will gradually weaken through the evening while
turning toward the NW at most terminals.

Outlook: After very brief drying Wednesday, moisture and unsettled
weather may quickly return Wednesday night into Thursday as a trough
of low pressure redevelops across the eastern part of the country. A
drier cold front will likely cross the region by the early weekend.

Confidence Table...

            22-04Z        04-10Z        10-16Z        16-18Z
KCLT       High  80%     High  83%     Low   56%     High  81%
KGSP       Med   69%     High  91%     Low   38%     High 100%
KAVL       High  94%     High  80%     High  90%     High  84%
KHKY       High  80%     High  80%     Low   45%     High  81%
KGMU       Med   69%     High 100%     Low   55%     High 100%
KAND       High  97%     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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