Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 180212

Area Forecast Discussion
National Weather Service Columbia SC
1012 PM EDT Sat Mar 17 2018

A cold front over North Carolina will push south into the
area late tonight then stall south of the CSRA on Sunday. The
front will become a warm front ahead of approaching low pressure
Monday. This low pressure will linger in the area through


An upper trough over the Ohio Valley will shift southeastward across
the Appalachians overnight...reaching the NC coast by morning.
The trough and most favorable energy will pass to our north. At
the surface...Low pressure over the NC mountains will move east
across NC overnight...reaching the Outer Banks by morning. This
will drag a backdoor cold front southward across the forecast
area late tonight into Sunday morning.

Convection moving into the SC mountains late this evening.
Airmass ahead of the storms is moist and unstable with dewpoints
in the 50s. Some of the high resolution models show isolated
convection crossing the Piedmont into the central Midlands.
Thus have indicated isolated storms crossing the Midlands in the
04Z-08Z time-frame. Models show the rainfall east of the area
by 09Z Sunday morning. Winds will stay up overnight due to a
strong low level jet, so fog is not expected to develop. The
temperature guidance was close with lows in the 50s.


Active weather pattern expected during this period as several waves
of energy move into the region with a stalled boundary in the

A weak backdoor front will sink south through the forecast area on
Sunday before stalling just south of the area across south central
GA. Forecast soundings indicate significant low/mid level dry air
across the area with little in the way of large scale lift due to
somewhat confluent northwesterly 500mb flow, so do not expect any
measurable precipitation with the frontal passage. The cooler air
will be relatively shallow across the southern half of the forecast
area so with mixing, still expect a warm day with highs on Sunday in
the mid to upper 70s south of I-26 while to the north, highs will be
in the upper 60s to lower 70s.

An initial wave of shortwave energy moving through somewhat zonal
mid level flow will cross the region Sunday night into Monday along
with increasing isentropic lift over the cooler airmass behind the
stalled front which will result in an in situ wedge. Precipitable
water values rise back over 1 inch but overall rain totals are not
expected to be significant due to expected convection along the
front to the south. Elevated instability will warrant the inclusion
of thunder in the forecast. The precipitation will help to reinforce
the wedge conditions with stable easterly low level flow over the
forecast area. The stalled front will begin to lift north as a warm
front on Monday as the main upper trough and surface low track
across the MS valley into the southern Appalachians. There is some
threat of severe weather across the southeast but will most likely
be confined along the front and in the warm sector, supported by
strong 0-6km wind shear greater than 40 knots. Current thinking
supported by forecast instability and soundings is that the threat
will be south of the forecast area through the day Monday but as
deeper mixing occurs and strengthening low level flow Monday night,
the warm front will surge northward. The question will be how much
instability will still be available during the overnight hours.
Damaging wind gusts and isolated tornadoes would be the primary
threat with any severe weather with the time frame of 02z-07z being
the most likely time period for our area to be possibly affected.
SPC has much of the forecast area in a marginal risk with slight
risk just to the south.

There appears to be a break in the action on Tuesday with warm
westerly flow in the wake of the warm front pushing through but A
secondary upper trough moving through the Gulf Coast states will
induce coastal low development late Tuesday and Tuesday night. This
will keep rain chances in the forecast and bring a front through the
area Tuesday night. Temperatures will generally be near to above
normal during the period.


The extended forecast period will feature below normal temperatures
early in the period with a mean upper trough along the east coast,
then transitioning back to near normal temperatures into the weekend
with upper ridging building over the region.

The upper trough over the forecast area will shift northeast of the
region on Wednesday but additional northern stream shortwave energy
dropping into the trough will keep the chances of rain in the
forecast through the day. The best chances of precipitation will be
across the northern half of the forecast area closer to the colder
air aloft and where slightly deeper moisture will be. Forecast
soundings and ensemble output from the ECMWF indicate that there is
a small possibility some snow may be able to mix with rain across
the far northern Midlands (Lancaster/Chesterfield) but confidence is
low due to uncertainty in models handling the complex evolution of
the storm system.

500mb heights begin to rise Thu/Fri across the region as the east
coast trough shifts offshore and upper ridging moves into the region
from the west. Some differences arise among the operational
GFS/ECMWF models by Saturday as the ECMWF holds the upper ridge
longer and keeping the next shortwave and associated front well west
of the area while the GFS brings another shortwave across the upper
midwest flattening the ridge and allowing a cold front and
associated moisture to push into the region.

Temperatures will be below normal through most of the period with
Wednesday likely to be the coldest day as the upper low moves out
with highs in the 50s to lower 60s and lows in the 30s Wed/Thu
nights. Temperatures moderate slightly going into the weekend with
highs in the mid to upper 60s by Fri/Sat and lows in the 40s.


Potent upper disturbance and surface wave will move SE along a
surface front to our NE tonight. This will keep surface winds up
some tonight and contribute to a strong low level jet. Will
include LLWS. A few strong to severe thunderstorms tracking SE
across the Upstate SC and NE GA. The expectation is that this
activity will weaken later tonight as it moves towards our
forecast area (FA), given that the best dynamics stay to our NE
and instability and shear values decrease some overnight.
Latest high resolution models indicate most associated
convective activity will remain to the N/NE of our TAF sites,
but a few showers or an isolated thunderstorm possible over our
FA. For now, will handle with VCSH and monitor trends on radar.
Enhanced low level moisture from recent rains leads to some
fog/stratus concerns. However, because of the wind and low level
jet and some cloud cover, will lean against mention of fog.
Mixed results in guidance regarding CIGs. For now, will maintain
VFR and reevaluate later trends and guidance for inclusion in
later TAF issuances if necessary. Surface boundary to move
through Sunday morning behind the departing surface low. Winds
will swing to north with diminishing speeds during the
afternoon. Fair/VFR Sunday with drier air coming in behind the

EXTENDED AVIATION OUTLOOK...Chance of showers late Sunday night and
Monday with deteriorating CIGs.  Chance of thunderstorms Monday
night, possibly severe. Chance of light rain and associated
restrictions Tuesday night and Wednesday.




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