Area Forecast Discussion
Issued by NWS Wilmington, OH

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160
FXUS61 KILN 080756
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
256 AM EST Thu Dec 8 2016

.SYNOPSIS...
Cold air will continue to get colder over the next day or two, and
temperatures will remain well below normal. Some flurries are
expected on Friday morning, before an area of high pressure moves
into the region late Friday into Saturday. On Sunday and Monday, a
complex low pressure system will through the Ohio Valley, bringing a
mix of rain and snow to the region.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A large and lumbering area of stacked low pressure is currently
located just south of James Bay, crossing slowly eastward through
Canada. This feature is dominating the longwave pattern across
much of North America, and is keeping the Ohio Valley in a regime
of deep-layer westerly/northwesterly cold advection flow. As is
unsurprising, the very weak 700mb disturbance moving through the
region right now is producing radar echoes but no precipitation --
the dry air below the mid-level clouds is evaporating the
hydrometeors as they fall. A dry forecast will be maintained
today, but with some question about cloud cover. There is a
considerable amount of upstream stratocumulus, which will likely
affect the northern half of the ILN CWA through the day, before
expanding across the whole area tonight. Further to the south,
drier 925mb/850mb conditions are expected, so sky cover will be
more of a question of any persisting mid-level clouds.

With some sun sneaking through in the southern / southeastern
sections of the forecast area, temperatures might be able to rise
to near or just above freezing. The forecast is much less
optimistic further north, where cold advection and persistent
cloud cover will combine to allow very little rise in
temperatures. The far northwestern ILN CWA -- currently in the
upper 20s -- may not reach values that high again through the rest
of the day. With a boundary layer that will be well-mixed, though
shallow, some wind gusts in the 15-20 knot range may occur at any
point throughout the day -- even into the evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
The short term forecast discussion will be updated shortly.

Previous discussion >
On Thursday the H5 low will be in ern Canada, with a sfc
trof/arctic front working down through the lakes.

As the sunrises, there should still be some mid and high clouds,
but they should pull e by mid day. During the afternoon, the
better H8 CAA will begin to work south of the Great Lakes and a
deck of sc will gradually overrun the area. Temperatures will
struggle to warm with the increasing cloud cover and caa. Highs
will range from the mid 20s in West Central Ohio to the lower and
mid 30s in the se counties.

As Thursday night progresses, H8 temperatures will drop to -12C
and the flow will align off Lake Michigan to bring flurries to
the region. Some snow showers will be possible in West Central
Ohio closer where the better fetch off of Lake Michigan may set
up. The pattern will linger into the first part of Friday, but
then the flow begin to back off of Lake Michigan and it should
bring a gradual end to the lake effect snow activity. At this time,
I am not thinking snow accumulations will be more than a dusting
if any.

The clouds and pcpn should help the temperatures from dropping too
low. Kept lows Thursday night around 20 degrees. Highs on Friday
will work only into the upper 20s to lower 30s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
High pressure centered over the Tennessee Valley on Saturday will
provide a dry forecast over the CWA, with enough breaks in the
clouds for some sunshine during the midday and afternoon. Despite
some sunshine, it will remain cold with high temperatures likely
remaining below freezing through much of the CWA except perhaps
south of the Ohio River into northern Kentucky where high
temperatures may hit/slightly exceed the freezing mark.

High pressure shifts to the east into the middle Atlantic states
Saturday night. Result will be a south/southeast flow in the low
levels and some warm advection which will allow for clouds to roll
back in Saturday evening and for precipitation to develop well ahead
of low pressure over the central Plains.

This low is forecast to move northeast into/through the Great Lakes,
eventually allowing a cold front to pass through Sunday night or
Monday morning. Until then, confidence has increased in a period of
precipitation Saturday night into Sunday and therefore have likely
pops across the CWA. Precipitation type will likely be snow at the
onset, but with some warmer air moving in from the south on Sunday,
expect snow to mix with/change to rain particularly south of
Interstate 70. GFS is colder than the ECMWF, and therefore used a
blended approach for p-type transition Sunday. Eventually, any
lingering precipitation would change back to snow Sunday
night/Monday morning as colder air moves back in behind the cold
front.

High pressure briefly builds in for Tuesday, but a fast-moving, weak
system may bring a chance of light precipitation by Wednesday,
although timing this far out is in question.

Below normal temperatures are expected for the long term forecast
period.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The center of a large scale upper level trough was located south
of James Bay Canada this morning. This feature will rotate
east/northeast through the day.

For this morning, considerable mid clouds will exit the region
around 12Z. Thereafter, CAA in conjunction with stratocumulus
clouds will advect/develop through the day as they move
southeast. It appears that the northern terminals will see some
MVFR ceilings by 18Z while the southern terminals remain VFR. An
increasing pressure gradient along with some diurnal mixing will
bring wind gusts into the 20-25 knot range.

For tonight, low level flow will shift to a northwest direction,
allowing cold air to move across the Great Lakes. This will allow
stratocumulus to thicken and lower overnight. There could be some
scattered flurries, with a few snow showers possible near the
northern terminals. Ceilings will all drop into the MVFR
category, with some models suggesting ceilings dropping below 2000
feet in some spots. Winds will remain a little gusty overnight,
but perhaps not as high as today with some night time
cooling/decoupling.

OUTLOOK...MVFR ceilings expected on Friday, which may linger into
Friday night. MVFR/IFR ceilings and visibilities possible Sunday
into Monday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$

SYNOPSIS...Hatzos
NEAR TERM...Hatzos
SHORT TERM...Sites
LONG TERM...BPP
AVIATION...Hickman



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