Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 160628

Area Forecast Discussion
National Weather Service Columbia SC
128 AM EST Sat Dec 16 2017

High pressure will be over the area through tonight 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.


Early this morning...Mostly clear skies will continue through
daybreak with confluent flow aloft. 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. Temperatures
are on track with lows still expected in the upper 20s west to
lower 30s east.

Today...Upper ridge will build over the region today while
surface high pressure slowly shifts east across the area. The
airmass will remain dry over the area with PWATs less than half
an inch. Highs during the day will be in the mid to upper 50s
under mostly sunny skies.


The flow aloft will be nearly zonal across the area, along the
northwestern periphery of a strong upper ridge centered over
the Caribbean. Surface high pressure will move toward the coast
tonight. Strong subsidence and limited moisture will keep rain-
free conditions in place. Clouds will start to increase
tonight as some weak moisture advection takes place on the back
side of the high. 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.

An upper ridge will build over the region today while high
pressure is centered over the area at the surface. This will
promote dry weather with mostly clear skies. No fog expected
early this morning due to dry air mass. Westerly winds will
continue at 6 knots or less through daybreak. 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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