Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS62 KGSP 172355

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
755 PM EDT Sat Mar 17 2018

Somewhat unsettled weather with normal to above normal temperatures
and chances for rain and/or thunder tonight and Monday night as
region experiences the passage of a number of shortwaves, along with
moisture increases.


As of 755 PM: Convection off the our west is still strong to severe
but the southern cells are showing some weakening. The northern
cells have maintained their intensity even though they area cycling
somewhat. Therefore, the current watch still look good where severe
storms will be more likely. Can`t rule out a severe storm with the
southern cells though. Latest convection allowing models keep the
northern cells strong as they cross the mountains and move east.
They also show redevelopment over the NC southern foothills then
moving across the CLT metro area. However, they disagree on how
strong those cells will be. The guidance also disagrees on whether
the southern cells can hold together and move into NE GA and the
western Upstate. The trends have been to weaken and dissipate those
cells as they move southeast. That said, latest mesoscale analysis
shows a tongue of MUCAPE developing along the I-85 corridor where
dew points have increased through the day into the evening. There`s
also quite a bit of effective bulk shear over this area as well. Of
course, we will continue to monitor and issue any products or
updates as needed.

Otherwise, the main short wave driving the storms will move quickly
SE overnight across the mtns and then nearly to the coast by 12Z
Sunday. The passage of the wave should take most of the precip
chances with it, except for a small chance in the pre-dawn hours on
the TN border owing to some lingering moisture. Min temps will
remain well above freezing so that would be all liquid. Expect
clearing sky around daybreak, with high pressure building in from
the NW. Temps are expected to be a bit tricky as we maintain a
gradient across the fcst area in the afternoon...above normal over
northeast GA/upstate SC, but below normal across the NW Piedmont.


As of 2PM EDT Saturday:  Fairly flat mid-level ridge is progressing
eastward across the region Sunday evening, with precipitation
associated with next upstream wave well to the west and southwest.
Fairly progressive upstream system dives into the south-central
CONUS with the precipitation ahead of it reaching the western parts
of the CWA early Monday morning.  At 12Z Monday, triple-point
surface low is near northeast Oklahoma with a warm front extending
southeast down the NC/GA stateline.  This warm front lifts northward
across the CWA on Monday, bringing an increase in BL moisture and
increasing chances for showers.  Cold front passes through the area
Monday night on the back side of the system.  Frontal passage will
be associated with the strongest chance for precipitation for this
event.  FROPA Tuesday morning will begin drying the BL and end that
round of precipitation, with dry northwesterly advection on Tuesday.
Main upper forcing from upper shortwave holds-off until Tuesday
evening, which will give some chance for light showers later on
Tuesday, despite low-level dry advection, especially over higher

Warm frontal passage on Monday will increase dewpoints enough to
create some CAPE Monday afternoon/evening, which along with good low-
level vertical wind shear, will creating some marginal chance for
strong thunderstorms, per the SPC outlook for day 3.

Temperatures will be seasonally warm on Tuesday, behind the warm
front and ahead of the cold front.  Once the cold/dry advection
kicks-in behind the front Tuesday night, temperatures will begin to


As of 235 PM EDT Saturday: the extended fcst picks up at 00z on
Wednesday with a deepening southern stream upper trof moving over
the fcst area while upper ridging builds over the Western CONUS.
As we move into Thursday, the upper trof appears to be reinforced
from the backside as it gradually drifts off the Southeast Coast.
The latest long-range model guidance has the trof axis lingering
just off the coast well into Fri and possibly into Sat, as the
upper ridge is flattened just to our west. At the sfc, a complex low
is expected to be centered over the region to start the period. This
system is expected to move off the Southeast Coast during the day as
Canadian high pressure slides in behind it from the north. The
models suggest that a decent amount of deeper-lyr moisture could
linger over part of the CWFA well into Thurs, as the low moves
farther offshore. By early Friday, things should be dry with high
pressure squarely over the region. The next low pressure system is
expected to move eastward out of the plains by the end of the period
and bring another cold front towards the fcst. The latest 12z GFS is
about 24 hrs faster than the ECMWF and Canadian with the approach of
the front, and has it moving thru the CWFA next Sat, whereas the
other 2 models have the fropa on Sunday.


At KCLT and Elsewhere: Convection off to the west is showing some
weakening as it moves toward the NC border. However, coverage has
not diminished. Convective allowing models still show the best chance
for TSRA at the NC sites. Therefore have retained the TEMPOs but
have adjusted the timing based on the latest radar and guidance. The
southern convection could survive long enough to effect the SC
sites, but chance is too low to include for now. Will of course
amend if the convection holds together. SW wind continues ahead of
the convection then turns NW behind. There will be some LLWS at KAVL
this evening. The wind then goes N and NE during the morning before
turning back to S or SE for the late afternoon/early evening. Do not
expect any restrictions except those associated with TSRA. That
said, there`s some indication of MVFR clouds developing by mid-
morning across the NC piedmont. If this does occur, it should
lift/scatter out by noon or shortly thereafter.

Outlook: Moisture returns again from the west with a complex low
pressure system on Monday and Tuesday. Colder air may wrap south
into the region behind the system on Wednesday and some mixed
precipitation cannot be ruled out. Restrictions will be likely in
the Mon-Wed period.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High 100%     High  88%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  92%     High  90%     High 100%
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:




AVIATION...RWH is the U.S. government's official web portal to all federal, state and local government web resources and services.