Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 161129

Area Forecast Discussion
National Weather Service Columbia SC
629 AM EST Mon Jan 16 2017

High pressure to the north will push a little cooler air into
the forecast area today. The high will be off the coast and a
southerly flow on the backside of the high will dominate
Tuesday bringing warmer weather again. A cold front and
associated moisture will be in the area Wednesday. Unsettled
weather will close out the week into the weekend.


Confluent 500mb flow over New England has resulted in a
strengthening of surface high pressure over the Mid-Atlantic
region which is re-establishing a weak backdoor front over our
forecast area this morning. Satellite imagery showing
widespread stratus developing and spreading northwestward from
the coast towards the Pee Dee and Piedmont regions on the cool
side of the boundary due to low level east to southeasterly
flow off the Atlantic.

Weak in situ wedge expected to develop across the forecast area
with higher confidence in the low clouds becoming established
and remaining in place through tonight across the northern and
central Midlands with lower confidence in the CSRA. Upper level
ridging will remain over the area today then flatten a bit and
shift to the east overnight as the storm system in the Plains
lifts into the western Ohio Valley and Great Lakes region by
late tonight. Not expecting too much in the way of
precipitation through early afternoon but increasing
atmospheric moisture and isentropic lift across eastern GA into
the Upstate this evening and overnight may result in an
isolated shower or two across the upper CSRA and western
Midlands so will hold on to slight chance pops there after 20z.

Temperatures will be cooler than Sunday where some record highs
were once again broken at CAE/AGS. Extensive lower clouds and
easterly flow will limit insolation with little sunshine
expected and highs should range from around 60 northern
Midlands to lower 70s CSRA. Overnight lows tonight will be in
the upper 40s to lower 50s.


Upper ridge holds through Tuesday afternoon before collapsing
Tuesday night as shortwave energy moves quickly through New
England followed by another shortwave trough that drops into
the Ohio Valley late Tuesday night. This second shortwave will
be the driving force that pushes a cold front southeastward
through the forecast area on Wednesday. Pooling moisture along
and ahead of the front with precipitable water values nearly
200-250 percent above normal will provide increased chances of
rain over the forecast area as the front pushes through. Model
guidance suggests there could be some weak instability
available to support an isolated thunderstorm but will be
dependent on low level clouds associated with weak wedge
eroding through the day and there is low confidence in that
occurring, at least across the northern half of the forecast
area. A limiting factor for significant precipitation is the
850mb wind direction from the west providing a bit of a
downsloping component. Model ensembles also showing significant
spread regarding pops leading to lower confidence but think the
spread is more related to timing differences of the frontal
passage. Drier air will briefly build over the region late
Wednesday through Wednesday night as surface high pressure
builds in.

Temperatures during this period will be well above normal
during this period with highs in the upper 60s to mid-upper 70s
and lows in the 50s. Cooler temperatures are expected behind
the front Wednesday night as some lows dip into the 40s but
this is still several degrees above average.


Active weather continues in the extended forecast period with
highly amplified 500mb pattern. Transient upper ridge will move
over the forecast area on Thursday as a deep closed low and
upper trough over the Plains strengthens with a significant
storm system developing over the Mississippi Valley. The upper
trough becomes negatively tilted Thurs night into Friday as it
lifts into the Ohio Valley and deep southerly flow off the gulf
moves east over the forecast area. The combination of strong
moisture transport along with upper level forcing from 500mb
height falls and PVA will bring another round of rain to the
area late Thursday night into Friday. A brief break is expected
Friday night in the wake of the passing upper trough but yet
another deep trough drops into the Plains and shifts eastward
Saturday night into Sunday bringing another wave of enhanced
moisture transport and chance of rain to the forecast area.
Generally south to southwesterly flow through the period will
continue to keep the warm temperatures over the region as we
remain well above normal for both highs and lows.


LIFR at most of our terminals expected this morning.

Weak back door front currently oriented NW to SE across the
western Midlands of SC. East flow behind the boundary, coupled
with low level moisture convergence, producing widespread low
cloudiness and fog near and to the east of the front across most
of SC. Fog and low cloudiness obscured on the satellite fog
channel by mid and high level cloudiness, but surface obs and
GOES derived flight category probability loops indicate area of
fog/stratus continuing to shift slowly westward. Some question
as to how far west it will spread this morning. Indications are
that the front and associated widespread restrictions will stay
just east of AGS/DNL. However, ahead of the front, areas of
radiation fog have developed, including at AGS though conditions
remain VFR at DNL. VSBYS are variable at AGS due to some mid
level cloudiness.

Back door front to shift slightly west towards the Savannah
River today where it appears will stall. Most guidance
restricting lowest CIGS this morning just east of the Sav R,
keeping it just east of AGS/DNL. However, due to uncertainty
will indicate some restrictions this morning at AGS/DNL.

With weak back door front/weak wedge over much of the
FA today, conditions appear will be slow to improve today,
especially at CAE/CUB. Latest high resolution models have
trended slower with return to VFR. Given weak wedge and little
precipitation reinforcement expected, will lean optimistic and
provide a return to VFR at CAE/CUB by mid to late afternoon.

Diurnal cooling plus abundant low level moisture combined and a
light SE low level flow will provide another good opportunity
for fog/stratus to redevelop again tonight, and it may begin
early with significant restrictions down to IFR to LIFR
appearing likely.

expected through Tuesday morning. Showers and associated
restrictions expected Wednesday through Friday.




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