Area Forecast Discussion
Issued by NWS Greer, SC

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357
FXUS62 KGSP 261809
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
209 PM EDT Sun Mar 26 2017

.SYNOPSIS...
Low pressure lifting from the Midwest to the Great Lakes will push a
band of moisture into the southern Appalachians today. Deeper
moisture and persistent southwesterly flow will then linger over the
southeast through Tuesday, with several rounds of showers and
thunderstorms possible. Drier air should briefly return by the
middle of the week as a cold front settles south of the region.
Another plains low pressure system will bring moisture back to the
southeast Thursday through Friday as weak cold air damming develops
east of the mountains.

&&

.NEAR TERM /THROUGH TONIGHT/...
1025 AM EDT Update...the main line of showers has been steadily
moving eastward across the CWFA over the past few hours with no sign
of thunder. This round of precip will likely move out of the fcst
area by the mid afternoon with only pockets of sct showers lingering
for the remainder of the day. Latest profiles remain pessimistic wrt
instability across the area, so unless cloud cover diminishes
significantly over the next several hours, it`s going to be
difficult to get much thunderstorm activity. Max temps could also
struggle to reach their fcst values today if cloud cover remains ovc
to bkn. Good moisture overnight should hold min temps 10 to 15
degrees above normal.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 245 AM EDT Sunday: A briefly closed 500 mb low pressure system
crossing the southern plains Sunday evening will open up over
Missouri on Monday and ride up the Ohio Valley through Monday night.
Deep layer southwest flow will keep fairly abundant moisture in
place on Monday ahead of this feature, but triggers for convection
will be hard to find. Still, SBCAPE values in excess of 1000 J/kg
will support scattered convection in the southwesterly flow. The
best upper support ahead of the system will cross the southern
Appalachians Monday night, but with weakening convective trends
given the loss of daytime instability.

The best omega with the passing upper support will move east of the
area by midday Tuesday. Meanwhile, a surface cold front will
approach the Appalachians from the northwest on Tuesday and settle
southeast across the region through Tuesday night. Anticipate the
best combination of lingering Tuesday PM instability and forcing to
occur across eastern sections, generally east of I-77. Some piedmont
locations could push 80 degrees for maxes Tuesday just ahead of the
front.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 255 AM EDT Sunday: Strong upper level ridging will cover the
eastern CONUS through Wednesday as yet another closed low pressure
system moves from the four corners region to the southern plains.
Meanwhile, surface high pressure will build southward from the Great
Lakes as a passing, weak cold front settles south of the forecast
area. Temperatures will remain warm on Wednesday, with plenty of
lower 80s in southern sections, as the thermal contrast across the
boundary is weak and insolation will be good.

The upper ridge will migrate across the forecast area on Thursday
and off the southeast coast Thursday night. At low levels, an
Atlantic moisture return will develop on Thursday and cold air
damming may onset as the returning moist upglide encounters high
pressure extending southward from a 1030 mb high center east of the
Appalachian mountain chain. Deeper upglide and moisture will then
arrive Thursday night through Friday as the upstream surface low
moves out across the mid/deep South early Friday and then crosses
the region around the retreating wedge, in Miller B fashion, through
late Friday. Instability should be uncovered from the south and
southeast on Friday as the wedge boundary retreats northward. This
could lead to a severe thunderstorm threat in southern sections if
the instability and shear appropriately line up. Will lean toward
the cooler side of the guidance envelope for Thursday and Friday
maximum temperatures.

Model differences increase Friday night into Saturday, but with a
consensus blend bringing a trailing surface cold front through the
area from the northwest after 12Z Saturday - ushering in drying.
Temperatures should rebound about a category Saturday as downsloping
flow develops east of the mountains.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
At KCLT: VFR conditions prevail thru the first part of the TAF
period with MVFR cigs from roughly 10z onward. I included a TEMPO
group for the first couple of hours for reduced visby and cigs
associated the rain showers currently moving over the area. I also
included a TEMPO group from 10 to 12z for early morning IFR visby
and cigs with MVFR cigs otherwise prevailing. Winds should remain
SLY thru the period before becoming more SWLY by the end of the
period.

Elsewhere: I kept cigs at MVFR for most of the period with periods
of IFR cigs during the early to mid morning hours. I also included
PROB30 groups for IFR and MVFR visby from roughly 08z onward but
these will likely be very hit and miss during that time. Otherwise,
I don`t expect conditions to improve to VFR again until after 18z.

Outlook: moist pattern with sly low-lvl flow will persist into mid-
week with another frontal system impacting the area late Monday into
Tuesday. This system will likely creating additional flight
restrictions across the region.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High  82%     High  81%
KGSP       High  98%     High  98%     Med   67%     Med   68%
KAVL       High  90%     Med   61%     Med   69%     High  80%
KHKY       Med   79%     High  89%     Med   76%     Med   79%
KGMU       High  98%     High  98%     Med   69%     Med   76%
KAND       High 100%     High 100%     Med   68%     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...HG
NEAR TERM...JPT
SHORT TERM...HG
LONG TERM...HG
AVIATION...JPT



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