Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 060924

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

A storm system along the Gulf Coast will move northeastward to
the Ohio valley spreading widespread rain over the forecast area
through today. Dry high pressure will briefly build across the
area for Wednesday. Another cold front will cross the region
Thursday bringing much colder air for the end of the week.


WV loop this morning shows vigorous s/w moving ne across the
Lower MS River Valley early this morning. Across the
Carolinas...the wedge of cool air continues to maintain itself
with ne/e low level flow and temperatures in the upper 40s north
to middle 50s south/southeast. Southeast radar loop shows
additional rainfall to move ne through the morning hours with back
edge near frontal boundary along MS/AL border. Models indicate
good isentropic lift to continue over the region through mid/late
morning...then weakening around midday. Will continue with
Categorical pops this morning with a gradual lowering of pops from
late morning into the afternoon. At the surface...wedge
conditions continue with depth at around 3 to 4 kt feet. Potential
for an isolated thunderstorm or two continues for the srn CSRA and
srn/ern Midlands from late this morning into the early afternoon
hours. Model show warm front to continue moving northward this
morning and eventually stalling along a line from near AGS to OGB.
LI pattern indicates some weak instability south of this line
during the period along with descent wind shear. Temperatures this
afternoon will quite tricky as always with slowly eroding wedge.
Have forecasted broad range from near 50 degrees across Lancaster
County to around 70 degrees across the sern portion of CWA.

By tonight...developing low pressure along the coast of the
Carolinas will become the dominate system and high pressure will
begin to move into the region. Model time sections show plenty of
moisture near the surface as mid/upper level dry out during the
late afternoon/evening hours. Have maintained some clouds
overnight...but could see some fog as well by morning. Stayed
close to consensus with temperatures dropping to around 40 north
to upper 40s south.


Dry and fair weather expected across the forecast area on
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 500mb
flow remains southwesterly with 850mb temperatures relatively
mild around +8C to +10C.

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 on Thursday.
Moisture is marginal along the front with precipitable water
values rising up to near 0.8-0.9 inches and the 850mb 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 on 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.


The extended periods will feature dry weather and well below
normal temperatures early in the period as a continental polar
airmass 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 on Friday with 500mb
flow becoming slightly northwesterly while neutral to slight cold
advection continues near the surface as Canadian high pressure
builds in from the northwest. This airmass will be the coldest we
have experienced this season with highly anomalous 850mb temps
around -5C to -6C and surface dewpoints falling into the teens.

Surface high pressure will reside over the area on 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 on Sunday.
There remain some timing differences among the deterministic
medium range models but the ensembles push a cold front across
the area sometime on 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 on Friday
and Saturday struggling through the 40s to possibly lower 50s on
Saturday with lows in the low to mid 20s Saturday morning and
only slightly warmer on 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.


Latest Southeast radar composite shows initial batch of rain
moving across much of the Carolinas and into southern GA.
Additional rainfall is developing farther southwest closer to s/w.
Expect widespread IFR conditions to develop overnight. Conditions
continue to be ifr/lifr across the region for ceilings with some
light fog. Shear will be on the increase associated with this jet
with the wedge front just south of the area. NAM still indicating
a potential for LLWS from the pre-dawn hours this morning to
around 18z. There may be isolated thunderstorms during the 15z to
18z time frame associated with the low-level jet and cooling aloft
ahead of an upper trough. This would mainly affect the taf sites
of AGS/CUB/OGB. However, the chance is still too low to include
in the terminal forecasts at this time. Precipitation should be
tapering off from the west by late Tuesday afternoon. Some
clearing skies tonight but potential exist for some fog.

The front will be east of the forecast area Tuesday night but
some lingering troughing and high low-level moisture combined with
nocturnal cooling may result in significant fog. Another cold
front may bring more showers and associated restrictions Thursday.
Breezy conditions may also be associated with the front.




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