Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181442

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1042 AM EDT Sun Mar 18 2018

Brief drying is expected today before moisture returns tonight and
lingers through midweek, as a strong low pressure system and a
secondary low pressure system bring unsettled weather and colder air
to the area. High pressure towards the end of the week will allow
for dry conditions to return.


As of 1030 AM: Current forecast is basically on track, but there
is some concern about high temps, especially over the NW Piedmont
and metro CLT. The problem is that we got a warmer start than
expected, so it stands to reason that we might get warmer than
expected this afternoon.

Otherwise, water vapor imagery shows the departing upper wave moving
off the eastern seaboard, while surface observations have the cold
front slowly slipping southward. 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 230 AM EDT Sunday: The short term forecast period begins
Monday morning as focus remains on the approaching potent storm
system we`ve been watching for the past few days. As the sfc low
moves eastward out of the central Plains, latest guidance continues
to place it`s extending warm front south of the FA Monday morning,
which is progged to propagate northward throughout the day. While
areas south/southwest of the FA will be more susceptible to severe
weather given the better instability/shear/dynamic support, as the
warm front moves closer to the FA into the afternoon hours, the
potential for thunderstorms (isolated severe) will increase as well.
Before the warm front provides it`s assistance in initiating
afternoon/evening convection, expect rainfall to already be
occurring across the FA Monday morning with the assistance of
isentropic lift.

Guidance suggests the sfc low will quickly move overhead late Monday
night as it`s associated cold front pushes through, allowing for
precip to linger into Tuesday morning. Behind this system, the
suggestion of a Miller B setup continues as another sfc low is
progged to develop across GA/SC/NC Tuesday afternoon ahead of a
secondary cold front just west of the FA. Do expect showers to
continue during the day with a gradual decrease in PoPs across the
Upstate and portions of the NW Piedmont into the evening hours as
the secondary front pushes through. With colder temperatures
advecting in behind the front, especially down the spine of the
Appalachians, anticipate a rain/snow mix along the TN border
beginning Tuesday night, carrying over into Wednesday morning. High
temperatures through the forecast period are expected to remain
below normal.


As of 345 AM EDT Sunday: Unsettled weather will continue well into
the beginning of the medium range forecast period which begins
Wednesday morning, as a sfc low continues to slowly make its way off
the Carolina coast. An upper longwave trough will settle in across
the eastern US for Wednesday and Thursday, as embedded waves of
energy travel within the trough axis, just south of the FA as
generally agreed upon across the models. With available moisture and
supportive dynamics, expect showers to be occurring Wednesday
morning, with a rain/snow mix in place along the TN border. Do
expect precipitation will gradually taper off by Wednesday evening
across the Upstate first, then the NW Piedmont, as the coastal low
slowly moves northeastward up along the eastern seaboard.

As Canadian sfc high begins to slowly build in behind the exiting
system, already colder temperatures in place along the TN border
will allow for a rain/snow mix to persist throughout the day, as a
transition to all snow is expected Wednesday night. Guidance begins
to disagree in regards to how long precipitation will last overnight
Wednesday, but have kept with the general trend of through just
before daybreak on Thursday.

Anticipate conditions to become dry and quiet for Thursday and
Friday as high pressure continues to build in, with an upper ridge
expanding across much of the US. Towards the end of the week,
another system is progged to move out of the central Plains into the
OH Valley, bringing another round of precipitation. However,
disagreement between the models continues both temporally and
spatially with this system. Temperatures throughout the forecast
period will remain below normal.


At KCLT: Plenty of low clouds are indicated in surface observations
just E/NE of the terminal this morning, but model profiles generally
suggest that the best cloud source will return from the N to NW with
900 to 850 mb VFR-level moisture. Expect NE winds early, toggling SE
this afternoon and persisting SE through early Monday. Upglide
moisture returns tonight with MVFR cigs spilling in from the
southwest after midnight along with light rain.

Elsewhere: Surface winds will adjust from NE toward southerly today
before adjusting back to easterly tonight as lower clouds, moisture,
and light rain return over an activating warm front. KAND to KAVL
will see the best chance of lower (IFR) overnight restrictions.

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...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High  95%     High 100%     High 100%     High  91%
KGSP       High 100%     High 100%     High 100%     Med   71%
KAVL       High  98%     High 100%     High  98%     Med   72%
KHKY       High 100%     High 100%     High 100%     High  96%
KGMU       High 100%     High 100%     High 100%     Med   67%
KAND       High 100%     High 100%     High 100%     Med   70%

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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