Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 251839
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
239 PM EDT Wed Apr 25 2018

.SYNOPSIS...
An area of low pressure will cross the region Thursday through early
Friday, bringing rain chances back to the area. High pressure will
build across our area this weekend and persist into early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 220 pm: Enhanced/expanding cu fields are noted east of the
mtns within axes of terrain/NW flow-induced convergence across the
foothills and Piedmont. CAMs continue to indicate spotty shower
development within these areas this afternoon, supporting a
continuation of 20-30 pops, although the highest pops will be
reserved for the TN border counties, where NW flow/upslope showers
are ongoing.  All showers should wind down around sunrise, with pops
diminishing to less than slight chance after midnight. Persistent
cloud cover should help maintain the trend of above-normal min
temps.

Another upper low will kick out across the Lower Miss Valley
tonight, gradually weakening and evolving into an open wave as it
moves across the Southeast on Thursday, reaching the Carolinas by
the end of the period. A convective band associated with strong
(albeit weakening) UVV within warm conveyor belt is expected to
begin moving into the forecast area from the west by noon-ish
Thursday. Although operational guidance is in good agreement
regarding the overall synoptic pattern, differences in the details
are fairly significant, especially regarding the surface response.
The NAM features a more intense surface cyclone (that moves across
our forecast area) along with a slower evolution, resulting in more
destabilization along with stronger shear parameters than in the
other operational guidance. If the NAM verifies closest to reality,
we will be dealing with a decent severe convective set up across the
area tomorrow afternoon into the evening, and the Day 2 Marginal
Risk recently introduced by SPC seems reasonable in light of
this.

Otherwise, likely to categorical pops overspread all but the eastern
zones by the end of the day, with one quarter to one half inch
rainfall amounts expected over much of the western half of the area
by the end of the period. Max temps are expected to be very close to
normal across the eastern third or so of the area tomorrow, with
denser cloud cover and increasing precip potential supporting a
forecast of up to 5 degrees below normal across the remainder of the
area.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 220 PM EDT Wednesday: the short term fcst picks up at 00z on
Friday with an upper trof axis lifting up and over the CWFA as another,
deeper trof dives down the backside of a much broader upper lvl trof
pattern. This second trof axis is expected to reach the fcst area early
Sat and move NE of the CWFA later in the day, however the region will
remain under the broader trof pattern into the extended period. At the
sfc, another low pressure system will move over the fcst area early Fri
and quickly lift north of the area thru the day. In its wake, drier
high pressure will gradually spread over the region from the west and
remain over the region into the extended period. As for the sensible
fcst no significant changes were made to the current fcst. It is notable
that SPC just updated their Day 2 Convective Outlook and now include all
of our SC zones in a Marginal Risk Area. The latest model runs are showing
increased amounts of sfc-based instability late Thurs/early Fri, so more
numerous thunderstorms are likely, however the severe potential still looks
low. Otherwise, precip chances remain high thru early Fri morning and then
taper off thru the rest of the day. High temps will be near normal for
both Fri and Sat, with lows a few degrees above normal each day.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
As of 145 PM Wednesday: No sigfnt changes were made to the going fcst.
Good confidence is had in the overall pattern beginning the period
which features a developing h5 ridge to the west supporting a stg
Canadian sfc high building into the FA. This high will be the main
synoptic feature thru the period as it slowly shifts east across the
southeastern states. With a stg sub inversion setting up and no
sigfnt moisture transport forced into the ridge...the atmos will
remain quite dry with weak flow thru the column. Max temps will
likely begin the period a little below normal as a llvl thermal trof
begins to modify. As the ulvl ridge shifts east Monday...increasing
thicknesses will rise and along with very good insol...max temps
shud have no problem reaching a cat or so abv normal thru the
period. Min temps will follow the same general trend with a seasonal
diurnal curve anticipated. Surface RH values will come close to FDS
levels across NE GA on Sunday...but besides that no fire wx concerns
are had with this fcst package.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
At KCLT and Elsewhere: Isolated to widely scattered showers are
expected to develop this afternoon across portions of the Piedmont,
with KCLT being the most likely to receive a direct hit. Tempos for
-SHRA are carried there from 19-22Z. Otherwise, SCT/BKN VFR stratocu
is expected through the evening, with cloud coverage increasing late
tonight into tomorrow morning. KAVL could experience some
restrictions late tonight/early Thu with a relatively moist
up-valley flow persisting, but conditions are expected to otherwise
remain VFR through the period. Winds will remain NW at 5-10 kts this
afternoon, becoming light overnight before turning toward the SE by
the end of the period.

Outlook: Moisture will return quickly to the region Thursday ahead
of a vigorous southern tier low pressure system. Rain showers/
possible thunderstorms and associated restrictions are expected to
begin developing Thursday afternoon, continuing into early Friday. A
drier cold front will approach from the northwest early in the
weekend, with dry/VFR conditions likely persisting into early next
week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  99%     High  88%     Med   71%     High  97%
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:

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...Carroll
NEAR TERM...JDL
SHORT TERM...JPT
LONG TERM...SBK
AVIATION...JDL



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