Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 061454
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
954 AM EST Tue Dec 6 2016

.SYNOPSIS...
Complex low pressure extending from the Ohio River Valley to
Southeast Coast will move northeast and be mainly off the Mid-
Atlantic Coast late tonight. Dry high pressure will briefly build
across the forecast area for Wednesday. Another cold front will
cross the region Thursday bringing much colder air for the end of
the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
The RAP surface-based LI pattern suggests the wedge of cool
air will linger through today supporting continued high low-level
relative humidity and associated low ceilings and fog. Radar and
satellite trends support much of the lift ahead of a mid-level
shortwave trough will shift east of the forecast area around
midday. There will be cooling aloft associated with the trough
which will help support continued scattered showers. There may be
enough instability for thunderstorms but based on radar and
satellite trends with the colder cloud tops well southeast of the
forecast area the thunderstorm chance is low. There will be strong
shear associated with the low-level jet just above the surface
wedge. If instability can possibility develop then severe
thunderstorms could occur.

Complex low pressure extending from the Ohio River Valley to
Southeast Coast will move northeast and be mainly off the Mid-
Atlantic Coast late tonight. The models show a weak pressure
gradient in the forecast area. Expect continued high low-level
moisture and with drying aloft and nocturnal cooling significant
fog will likely develop as indicated by most of the NAM and GFS
MOS and a significant number of SREF members. Followed the
guidance consensus for the temperature forecast.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Dry and fair weather expected across the forecast area Wednesday
in the wake of the departing system with weak high pressure trying
to build into the region. Temperatures will be slightly above
normal with highs in the 60s Wednesday as 500 mb flow remains
southwesterly with 850 mb temperatures relatively mild around +8 C
to +10 C.

The next weather system will begin to take shape late Wednesday
as an upper trough moves east across the middle of the country
and drives a cold front across the forecast area Thursday.
Moisture is marginal along the front with precipitable water
values rising up to near 0.9 of an inch and the 850 mb flow
becomes westerly to slight northwesterly as the front approaches
further limiting the rain chances, despite favorable upper
dynamics with the right entrance region of the jet present. Will
continue to carry slight chance to low chance pops late Wednesday
night into Thursday. Temperatures will warm ahead of the frontal
passage Thursday with highs ranging from the upper 50s western
Midlands to lower to mid 60s eastern Midlands.

Strong cold advection Thursday night under clearing skies should
allow temperatures to fall into the upper 20s to lower 30s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
The extended period will feature dry weather and well below
normal temperatures early in the period as a continental polar
air mass settles over the region, followed by increasing chances
of rain by day 7 Monday as the next weather system approaches.

The upper trough axis will cross the region Friday with 500 mb
flow becoming slightly northwesterly while neutral to slight cold
advection continues near the surface as Canadian high pressure
builds in from the northwest. This air mass will be the coldest
we have experienced this season with highly anomalous 850 mb
temps around -6 C and surface dewpoints falling into the teens.

Surface high pressure will reside over the area Saturday before
shifting offshore Saturday night in response to shortwave energy
moving eastward across the middle of the country with cyclogenesis
occurring over KS/OK Saturday night, then deepening and lifting
northeastward into the Great Lakes region Sunday. There remain
some timing differences among the deterministic medium-range
models but the ensembles push a cold front across the area
sometime Monday, tapping moisture off the Gulf of Mexico. Will
continue to highlight increasing pops Sunday night and peaking on
Monday but keeping pops in the chance range.

Temperatures during this period will be cold with highs Friday
and Saturday struggling through the 40s to possibly lower 50s Saturday
with lows in the low to mid 20s Saturday morning and only slightly
warmer Sunday morning. Cannot rule out possible record lows
Saturday morning. Temperatures will moderate warmer Sun/Mon back
to near normal values with highs in the upper 50s into the 60s and
lows in the 40s.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Expect widespread IFR/LIFR conditions through much of the TAF
period. The RAP surface-based LI pattern suggests the wedge of
cool air will linger through today supporting continued high low-
level relative humidity and associated low ceilings and fog. Radar
and satellite trends support much of the lift ahead of a mid-level
shortwave trough will shift east of the forecast area around
midday. There will be cooling aloft associated with the trough
which will help support continued scattered showers. There may be
enough instability for thunderstorms but based on radar and
satellite trends with the colder cloud tops well southeast of the
area the thunderstorm chance is too low to include in the terminal
forecasts at this time. There should be significant shear
associated with the low-level jet just above the surface wedge.
Based on the NAM and KCAE 88D trends we have included LLWS in the
terminal forecasts. Drying aloft with continued high low-level
moisture plus light wind and nocturnal cooling supports IFR fog
overnight as indicated by most of the NAM and GFS MOS and a
significant number of SREF members.

EXTENDED AVIATION OUTLOOK...
A cold front with little moisture will move through the area
Thursday. Breezy conditions may be associated with the front.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

$$
SYNOPSIS...99
NEAR TERM...99
SHORT TERM...99
LONG TERM...99
AVIATION...99



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