Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 090217

Area Forecast Discussion
National Weather Service Indianapolis IN
917 PM EST Fri Dec 8 2017

The AVIATION Section has been updated below.


Issued at 257 PM EST Fri Dec 8 2017

Snow will overspread the area late tonight and Saturday as a
clipper system moves through the Great Lakes. Temperatures will
generally run cooler than normal in the northwest flow pattern,
and a series of upper waves moving through the main trough will
bring periodic chances for precipitation.


.NEAR TERM /Tonight and Saturday/...

Issued at 257 PM EST Fri Dec 8 2017

Forecast focus is on arrival of snow with approaching clipper
system and amounts. Models are in good agreement on holding off
any precip until after 6z (1 am EST). Models are actually moving
snow in slower than previous runs, and now looks like northwest
counties could see arrival after 3-4 am, with central counties
seeing snowfall arriving around 6-8 am and eastern counties around
8-10 am.

Synoptic forcing from the upper wave will move through the area
and be off to the east sometime around 15-18z, but models are
indicating some mesoscale features developing as the synoptic
forcing moves off. Snow squall parameter, along with frontogenesis
indicates some brief potential for squall conditions around
developing around 18-21z and dropping off by 0z if not before.
Lack of moisture will still likely limit amounts, but a large snow
ratio of 15 to almost 20 to 1 will make for a light fluffy snow.
The biggest hazard during the late afternoon will likely be rapid
changes in visibility in short distances as drivers come upon
these squalls (assuming they develop).

Overall for amounts still only at moderate confidence, as model
solutions have been bouncing back and forth from a little more to
a little less with each set of runs. Right now think most likely
scenario is around an inch across central and southeastern
portions of central Indiana, with half an inch or less southwest,
and around 2 inches in the far north and northeast. Could see a
lake effect band or the aforementioned squalls produce locally
higher amounts, probably not exceeding 3 inches (for IND forecast
area) and certainly not widespread.

Lows tonight should drop into the upper teens east to lower 20s
central and west with the arrival of clouds from the west later
tonight bringing an end to cooling. Saturday expect highs to be a
little colder than a guidance average due to dry air causing
cooling upon precip onset. Looking at highs in the upper 20s to
lower 30s.


.SHORT TERM /Saturday night through Monday/...

Issued at 257 PM EST Fri Dec 8 2017

Backing of the winds Saturday night should bring any lake effect
snow showers that manage to reach the northeastern counties to an
end. Forcing will stay north of the area with the next wave
approaching Sunday night/Monday and this will just bring a slight
chance for precip into the northern counties for Monday morning.
Temperatures will warm a bit for Sunday and more for Monday,
possibly climbing to near/a bit above normal under flatter flow.


.LONG TERM /Monday Night Through Friday/...
Issued at 220 PM EST Fri Dec 8 2017

Models are close enough that the model blend initialization
was accepted for most items.

The eastern half of the country will remain under an upper trough
through the long term. A series of waves will ride through this
trough, bringing occasional chances for precipitation through the

Of course there are timing and some location differences between the
models, but there is too much uncertainty that far out to try and
pick a favorite. Thus kept the intialization`s PoPs intact.

The intialization is again too warm later in the long term as it
trends toward climatology, so cut temperatures as needed there.


.AVIATION /Discussion for the 09/03Z TAF Update/...

Issued at 915 PM EST Fri Dec 8 2017

No changes.

Previous Discussion...
VFR conditions will prevail through daybreak tomorrow. However,
a quick clipper system will bring light snow to central Indiana
tomorrow morning and afternoon. During that period, visibilities
and ceilings will deteriorate to MVFR levels. Meanwhile, winds
will veer from the southwest to northwest, becoming strong by
tomorrow afternoon with sustained speeds of 12 to 16 kts and gusts
up to 27 kts.





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