Area Forecast Discussion
Issued by NWS Greer, SC

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198
FXUS62 KGSP 281053
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
653 AM EDT Fri Apr 28 2017

.SYNOPSIS...
Warm and humid high pressure will remain over the forecast area
before a cold front pushes in from the west early Monday. Weak yet
dry high pressure builds in early Tuesday and crosses the southeast
states into Wednesday. A moist sfc low may affect the region by
Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM EDT: Pre-dawn visibility values have crashed to 1/4SM
or less in many locations across the foothills of the western
Carolinas. A Dense Fog Advisory has been issued for these areas. Mid
and upper level drying atop the very moist boundary layer is also
producing spotty dense fog elsewhere and this will be featured in an
SPS through mid-morning.

Otherwise, deep layer southwesterly flow is in place aloft over the
southeast, with a weak surface boundary stalled over the western
Carolinas. Any thermal/moisture contrast across this boundary should
continue to dissipate through the day. Upper level heights will
gradually rise over the area as an offshore ridge axis becomes
resurgent. Little to no upper level triggering should be available
through the period. Very warm profiles in the 5 to 10 kft layer
should effectively cap off deep convection, which is fortunate since
elevated CAPE above the capping looks very robust this afternoon.
Will keep any isolated shower mention confined to the immediate
southerly upslope areas this afternoon. Temperatures should rebound
solidly into the 80s today, with some lower mountain valleys just
about as warm as piedmont sections this afternoon in the southwest
flow. Another mild night with areaas of fog is expected again
tonight.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 200 AM Friday: A stacked Bermuda High pattern will dominates
the  FA thru the short range. By Sat afternoon...a 593 DM high will
be positioned off the Atl coast and an associated llvl high will
ridge across wrn GA. Return flow around the sfc high will bring just
enuf moisture to the area for mainly upslope -shra/tstms. The NAM is
still dry during this time...so pops are held low. The models show
mod/stg sbCAPE within low shear...so expect some pulse stg/svr
storms into the late afternoon. Max temps will be in the mid to
upper 80s non mtns. On Sun, the sfc ridging eases off slightly...but
enuf to allow better GOM moisture flux across the entire FA. Max
temps will be a bit lower due to increased multi layerded
moisture...but sfc td/s will remain high. Soundings show much less
instability...yet shear will be slowly increasing thru the overnight
period. Think there will be enuf destabilization for another round
of deep shra and pulse-type tstms with a bit better overall coverage
than Sat.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 225 PM EDT Friday: Not much change to the previous fcst. The
models are in decent agreement with the timing of the fropa Mon. The
GFS is deeper with the ulvl low than the ECMWF/CMC solns yet
not enuf to expect major differences in the sensible weather fcst.
Will count on a weakly forced front to work into the mtns early in
the day...then swing east of the FA btw 00z-03z. There shud be
decent coverage of -shra/tstms with a few stg/svr storms possible in
a high shear / low cape environ. The main concern will be possibly
damaging winds as 50 kt h85 jet develops along the sfc convg zone
while weak accelerations are noted within the HGZ. Noticeably lower
sfc td/s will work in from the west during the day making for
pleasant yet breezy conds on the back side of the front. A small
scale srn stream high crosses the region Tue into Wed and temps will
slowly heat up...but generally remain arnd or a bit above normal.
The next good chance for precip and tstms will be late Wed into Thu
as a developing sfc low works toward the region. There are sigfnt
model differences wrt to the track and timing of this feature so
pops have been reduced into the mid chance range Thu.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
At KCLT: Moisture has been deep enough thus far to favor MVFR
stratus development versus dense fog. Given the drying aloft, a
period of IFR ceilings and MVFR fog is likely at times through at
least 14Z. Low clouds and fog will be slow to scatter through the
morning hours, with recovery to VFR not likely until around 16Z.
Expect some low end gusts in the SSW flow with mixing this
afternoon. Warm profiles aloft should preclude any afternoon
convection near the airfield. Low clouds and fog will be possible
again tonight.

Elsewhere: Low clouds and fog are in place across the mountain and
foothill TAF sites at daybreak, with at least tempo VLIFR conditions
expected at times through 14Z. Anticipate very slow recovery through
the morning hours, with lower end VFR conditions not likely until
around 16Z most locations. Expect S to SW winds generally less than
10kt throughout, but with a few low end gusts possible with mixing
this afternoon. Another round of low clouds and fog is likely
tonight.

Outlook: Areas of fog will be possible each morning as the near
surface layer remains moist through the weekend. Diurnally-based
showers and thunderstorms will possible Saturday and Sunday, with
more organized thunderstorms possible by Monday.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High  83%     High  80%     High 100%     High 100%
KGSP       High  89%     High  95%     High 100%     High 100%
KAVL       High  83%     High  90%     High 100%     High 100%
KHKY       Med   72%     High  80%     Med   60%     High 100%
KGMU       High  89%     High  95%     High 100%     High 100%
KAND       High  94%     High  90%     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...Dense Fog Advisory until 10 AM EDT this morning for NCZ035-056-
     068-069-502-504-506-508-510.
SC...Dense Fog Advisory until 10 AM EDT this morning for SCZ004>008-
     010.

&&

$$
SYNOPSIS...SBK
NEAR TERM...HG
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...HG



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