Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 152336

Area Forecast Discussion
National Weather Service Columbia SC
636 PM EST Fri Dec 15 2017

High pressure will move into the forecast area from the west
tonight. The high will be over the area Saturday and Saturday
night and then shift off the Southeast Coast Sunday. There will
be increased moisture in the southerly flow on the backside of
the offshore high Monday.


The models suggest the mid and high cloudiness will diminish
late tonight in the wake of a shortwave trough plus h5 confluent
flow. The near-surface layer will remain dry associated with
the ridge moving into the area from the west. The dry air mass
should help prevent fog during the early morning hours. Followed
the guidance consensus for the temperature forecast and expect
lows mainly in the upper 20s and lower 30s.


The flow aloft will be nearly zonal across the area, along the
northwestern periphery of a strong upper ridge centered over
the Caribbean. Meanwhile, surface high pressure will slowly
shift across the area Saturday and move toward the coast
Saturday night. Strong subsidence and limited moisture will keep
rain-free conditions in place. Clouds will be few on Saturday,
but start to increase Saturday night as some weak moisture
advection takes place on the back side of the high. Highs during
the day will be in the mid to upper 50s, with nighttime lows
reaching the lower to mid 30s most areas.

On Sunday, the upper-level ridge will strengthen over the
region as the surface high shifts into the western Atlantic.
Moisture will deepen over the area, resulting in skies becoming
mostly cloudy. Rain chances look to hold off during the daytime
hours, but a front lifting from the southwest and the deeper
moisture could bring some rain to the area by later Sunday night
and the forecast indicates chance PoPs across much of the area
as a result. Expect mild temperatures because of the southerly
flow during the day and cloud cover at night, with highs in the
lower to mid 60s and lows in the mid 40s to lower 50s.


There is considerable uncertainty in the long-term period due
to significant model differences and somewhat poor run-to-run
consistency, leading to a lower than normal confidence forecast.

The surface boundary appears to become nearly stationary either
over or in close proximity to the area Monday and Monday night,
resulting in probably the greatest rain chances of the week
with the forecast showing high chance or likely PoPs. Then,
models really begin to differ as the GFS has a more progressive
synoptic pattern into midweek whereas the ECMWF is much more
amplified. It seems best to take somewhat of a blend where
possible, maintaining chance PoPs into Wednesday, then show some
drier conditions into Thursday before rain chances increase
late week ahead of the next front. Temperatures generally appear
to remain above normal through the long-term period.


High confidence in VFR conditions at all terminals throughout
the 24-hr TAF period.

High pressure will continue to build into the area from the west
overnight as 500mb shortwave energy crossing the Appalachians
moves to the coast. Satellite imagery shows a blanket of high
clouds continuing to stream over the area from the southwest
which will remain over the terminals through around midnight or
so. These clouds should shift to the south later tonight as mid
and upper level flow becomes more northwesterly. No fog
expected tonight due to dry air mass. Westerly winds around 5 to
10 knots will continue through around 03z-05z before subsiding
to less than 5 knots. Winds will pick up again by 16z from the
southwest around 5 to 8 knots.

EXTENDED AVIATION OUTLOOK...Unsettled conditions possible early
next week with lower ceilings and restricted visibilities
possible in rain at times Monday through Wednesday.




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