Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180609

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
209 AM EDT Sun Mar 18 2018

Brief drying is expected today before moisture returns tonight and
lingers through at least Tuesday ahead of a strong low pressure
system arriving from the plains. Colder air may wrap into the region
by mid-week behind the departing low, with dry high pressure
returning through late week.


As of 155 AM: Water vapor imagery shows the passing, strong upper
shortwave crossing the southern Appalachians at issuance time. The
best lingering forcing is over the piedmont where deep layer DPVA is
passing over the frontal zone sagging southward. Any lingering
showers and isolated thunderstorms should end quickly through 3 am.

Otherwise, shortwave ridging will build over the southeast today
into tonight, while a strong closed low forms over the southern
plains. At the surface, the passing cold front will settle south of
the region today before returning north as a warm front tonight.
Fairly good insolation is expected in all but the northeast parts of
the area, where better 850 mb moisture will linger in the northerly
flow. Plenty of 70s temperatures are expected this afternoon in the
southern half.

850 mb flow will gradually return to light southerly late today and
provide some returning upslope moisture and associated cloudiness
along the eastern Blue Ridge by evening. Better low to mid-level
moisture ahead of the plains system will return late tonight along
an activating warm front, and continued weak low level upglide
should permit light rain to start breaking out atop region during
the early morning hours Monday.


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: Any lingering convection early this morning
will remain southeast of the TAF sites, and continue to move
southeast away from the area, as the surface frontal boundary
settles southward and the upper support moves away to the east. Some
MVFR restrictions on northeasterly flow this morning could flirt
with KCLT, but will generally stay northeast of the terminal.
Otherwise, VFR conditions will persist, but with ceilings
redeveloping in moist upglide tonight, with rain chances
redeveloping generally after 06Z. Winds will toggle N to NE as the
front settles south, but with southeast winds returning to KCLT
through the day, and southerly flow redeveloping from KAVL to KAND.

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...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High 100%     High  98%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  93%     High  95%     High 100%     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:




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