Area Forecast Discussion
Issued by NWS Greer, SC

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161
FXUS62 KGSP 291842
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
242 PM EDT Mon May 29 2017

.SYNOPSIS...
A series of weak cold fronts will cross the area through mid week.
Weak high pressure will make Thursday the drier day of the week.
Expect a stronger cold front to reach our region over the weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 230 PM EDT Memorial Day: Surface trough in place across the
Piedmont with approaching shortwave moving out of the Deep South and
a bit of an upper jetlet are the main forcing mechanisms for
convection this afternoon.  Deep upper trough/low over Lake Superior
and upper high just east of the Bahamas has led to strong
southwesterly fetch aloft, helping to draw moisture out of the Gulf.
CAMs and other hires guidance have for hours been initiating
convection right about now (and seeing some higher reflectivities
over the mountains at AFD time), spreading it east across the Blue
Ridge and Piedmont through the afternoon/early evening. Some of
these runs have looked fairly intense, but then again just about all
of these near-term guidance members are initializing CAPE values way
too high; in reality sbCAPE has been held down a bit especially
across the NC Piedmont due to a bit of warming aloft, just above
400mb, which should slowly be overcome through the afternoon as
surface temperatures continue to rise. Lapse raters not particularly
impressive right now but enough synoptic forcing and aforementioned
surface heating should result in rapidly steepening low-level lapse
rates, and with the upper jet moving across, there should be enough
bulk shear to organize convection into multicell clusters. Main
threat remains gusty/damaging winds, though some low-end hail cannot
be ruled out. Also seeing convection develop in E AL that should
lift slowly NE, so in addition to convection initiating in situ,
convection approaching from the SW will push into NE GA/Upstate SC
tonight. While not a significant concern, at least minor hydro
threat cannot be ruled out with any training cells, and have bumped
up QPF accordingly.

Convection should wane overnight and we lose most of our deep-layer
forcing as we push into tomorrow, but surface trough remaining in
place and southwest flow aloft continuing will allow for diurnal
convection, possibly enhanced a tad with the proximity of the trough
aloft. Best chances for Tuesday remain across the Piedmont
(especially SC/GA where the trough will linger) and the SW
mountains. Guidance is trending cooler for tomorrow but we`re
warming up more than anticipated today so have erred on the warm
side, but still right at seasonal normals. Lows tonight a handful or
so degrees above.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 200 pm Monday: At long last, the axis of the upper trough,
that has been over the central Conus for what seems like ages, will
finally push to the East Coast by the end of the short term. This
will drag a weak cold front through our area on Wednesday. While
this should provide a focus for deep convection Wed afternoon,
coverage may not meet the expectations of a typical late-spring
fropa. Progged mid-level lapse rates are very poor, while forecast
soundings depict a well-mixed/relatively dry boundary layer. As a
result, no short term guidance source depicts anything more than
modest levels of CAPE Wed afternoon and pops will be advertised only
in the 20-30% range across much of the area (maybe 40% in the high
elevations near the Blue Ridge). Deep layer shear will remain
somewhat respectable, so a severe storm or two cannot be ruled out,
but the threat should be limited by the overall lack of robust
buoyancy.

By Thursday, guidance suggests weak but relatively dry high pressure
should be building into the area, limiting diurnal destabilization.
In fact, most guidance produces little or no qpf response across our
area Thu afternoon. Pops will be limited to a slight chance across
roughly the southern half of the area (closer to the departing
frontal zone). Temps will generally remain close to normal, perhaps
a degree or two above, through the period.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 210 PM Monday: A deep SW flow out of the Gulf will develop
Thursday night and persist into the weekend. The persistent upper
level closed low and trough over eastern Canada will rotate and
surge a bit further south during the weekend with axis roughly along
the East Coast. A surface cold front will be pushed south with
moderately strong high pressure dropping down from the western Great
Lakes. This cold front will be the focus of more widespread
convection as it reaches our region late Saturday night and Sunday
morning. If this scenario occurs with front arriving in the cooler
part of the day, this should prevent stronger convection. Of course,
this is nearly a week away and timing of frontal passage could speed
up or slow down. Some strong convection ahead of the cold front may
reach the NC mountains Saturday evening before weakening Saturday
night. Late Saturday is the best chance of severe with prefrontal
forcing and effects of convective generation from diurnal max
heating. Drier air should filter in from the north by late Sunday
night. The front should stall out over Florida to start the upcoming
week with drier weather for at least a couple of days.

Max temps are forecast to be near normal and Min Temps forecast to
be about 5 degrees above normal due to the cloud cover and higher
moisture level preventing radiational cooling.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Guidance all still has convection blossoming
across the Blue Ridge in the next couple of hours and spreading east
across the area through the afternoon/evening. Have timed TEMPO TSRA
as close as possible, including VRB gusty winds as that is the main
threat in any strong/severe storms. Generally VFR through the
evening except in any TSRA, but with cigs becoming BKN-OVC 5-7kft.
could see some MVFR cigs/vsby in the predawn hours on Tuesday.
Introduced another PROB30 at most sites starting 15z Tuesday with
more typical diurnal convection expected.

Outlook: Primarily afternoon and evening TSRA are possible each day,
bringing periodic restrictions. Areas of morning fog and/or low
stratus may potentially develop especially where RA fell the
previous evening. This pattern will continue through at least the
end of the work week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High  97%     High  83%     High  89%
KGSP       High 100%     High 100%     High  85%     Med   78%
KAVL       High  99%     High  91%     High  83%     High  87%
KHKY       High  97%     High  98%     High  88%     High  96%
KGMU       High 100%     High 100%     High  83%     Med   76%
KAND       High 100%     High  98%     High  98%     High  87%

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...DEO
NEAR TERM...TDP
SHORT TERM...JDL
LONG TERM...DEO
AVIATION...TDP



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