Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 271043

Area Forecast Discussion
National Weather Service Columbia SC
643 AM EDT TUE SEP 27 2016

A cold front will slowly push into the area late Tuesday into
Wednesday and cross the area Wednesday night. Cooler and drier
more seasonable temperatures expected late in the week and over
the weekend with little rain chances.


Latest analysis depicts the cold front extending from eastern
West Virginia southwestward along the spine of the Appalachians
into northeast Alabama. An axis of enhanced moisture at 700mb was
nearly collocated with the precipitable water axis extending from
east-central Virginia through the piedmont region of the
Carolinas. Precipitable water values remain above normal for this
time of year around the 90th percentile with abundant low level
moisture present with dewpoints in the upper 60s to lower 70s.
Regional radar showing dissipating showers across the northern
Midlands while showers continue to develop along the coast
associated with a weak offshore surface low.

Water vapor imagery shows shortwave energy rounding the base of
the upper low and model forecast lift this feature northeast of
our area and the mid level flow remains from the southwest nearly
parallel to the cold front and this will prevent much eastward
progress of the front today. There is reasonable agreement among
the operational model suite and hi-res CAMs that convection will
develop in the warm sector ahead of the front over the higher
terrain of NC/SC during peak heating and then move eastward late
afternoon and evening into the northern and western Midlands.
There is not much upper support to enhance convection but should
be enough instability to support unorganized scattered convection
late afternoon and evening mainly across the northern and western
parts of the forecast area so will continue to carry highest pops
there with lower pops elsewhere. Weak surface low offshore will
also lift northward through tonight and limit convergence along
the seabreeze. Cannot rule out an isolated strong to severe storm
but like yesterday the overall severe threat appears low. The high
moisture content and possible training of convection may lead to a
limited isolated flood threat especially in the northern Midlands
where recent rain has fallen.

Temperatures will remain well above normal with afternoon highs
once again expected in the mid to upper 80s with strong
insolation. Debris clouds and abundant boundary layer moisture
will limit overnight lows tonight as temperatures are expected to
be in the upper 60s to lower 70s.


The closed upper low over the Great Lakes region will dive
southeastward into the Ohio Valley Wednesday and Wednesday night
resulting in 500mb height falls across the forecast area and
increasing lapse rates as cooler air aloft overspreads the region.
The cold front that has been hung up in the mountains will provide
a focus for convection and with increasing winds aloft and a
moderately unstable atmosphere expected Wednesday, the threat of
organized convection is increasing. SPC has outlooked the area in
a marginal risk for severe storms with the main threat being
damaging winds. The drier air that had been forecast to move into
the area over the past couple of days looks to be a bit delayed
more into Wednesday evening now further supporting convection
during peak heating Wednesday. Have increased the pops across the
area although keeping them below likely due to some uncertainty in
amount of instability and resulting coverage of convection.
Temperatures should again remain warm with highs in the mid to
upper 80s as the region will be in the warm sector southeast of
the front.

The front is expected to cross the area sometime Wednesday night
and drier air will move into the region from the west ending
precipitation as cooler air builds in. Overnight lows will range
from the upper 50s west to mid 60s east.


Little change made during this period. Closed upper low will
meander around western NC and eastern TN on Thursday before
lifting back northward on Friday. Despite the proximity of the
upper low and associated cold temperatures aloft, moisture will be
quite limited with precipitable water values below an inch and
some downsloping low level flow which should preclude any diurnal
convection. Expect cooler temperatures closer to normal values
with diurnal cumulus each day Thu/Fri.

Generally fair weather expected over the weekend into early next
week with the upper low lifting away from the region replaced with
nearly zonal upper level flow and weak high pressure at the
surface. One feature that will need to be monitored though will be
the tropical wave moving towards the Lesser Antilles which could
be approaching Cuba or the Bahamas by the middle of next week.

Temperatures will be near normal with highs around 80 to the lower
80s and lows in the 50s.


Some potential for fog/stratus early this morning, though
confidence limited. Despite moist low levels, light surface winds,
and some guidance suggesting fog/stratus development, significant
restrictions have yet to develop, except at fog prone AGS. This
perhaps is due to some mid/high level cloud cover.

After any morning restrictions, VFR expected today outside of
scattered afternoon/evening showers and a few thunderstorms, which
are expected to develop along a slow moving prefrontal trough, and
remain mainly north of the terminals. For now, think VCSH will
suffice.  Confidence in restrictions late tonight/early Wednesday
morning too limited to include in the 12Z TAFs at this time, due to
uncertainties with regards to cloud cover.

EXTENDED AVIATION OUTLOOK...Some potential for fog/stratus late
Tuesday night/early Wednesday morning. Chance of showers and
possible thunderstorms, and associated restrictions, Wednesday
afternoon. No impacts to aviation expected Thursday through




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