Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 110547
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1247 AM EST Mon Dec 11 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EST Sun Dec 10 2017

An Alberta clipper will bring snow with light accumulations of an
inch or two Monday. It will become windy and much colder behind
this system Monday night through Tuesday with accumulating lake
effect snow mainly near to west of US-131. The coldest airmass of
the season will move in Tuesday through Thursday when high
temperatures will only reach the lower to middle 20`s.

&&

.UPDATE...
Issued at 1006 PM EST Sun Dec 10 2017

One batch of light precipitation was working its way through the
Lansing to Jackson region. It looks like there was some freezing
drizzle occurring there. That should move southeast of Jackson in
the next hour or so. There was another batch dropping down from
the Newaygo to Big Rapids area. This looks like snow at this
time. I did update to forecast to reflect any patchy freezing
drizzle transition to snow flurries. We did issue an SPS to over
any localized impacts and updated the HWO and Weather Story.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 330 PM EST Sun Dec 10 2017

An Alberta clipper system will cause snow to develop from west to
east across our fcst area during the mid to late morning hours
Monday just after the morning commute. The snow will continue
into the afternoon with accumulations of one to two inches across
the vast majority of our fcst area and isolated higher amounts to
near three inches possible.

This synoptic snow will taper off during the mid to late afternoon
hours. Then an upper level disturbance will bring a brief period of
snow near to mainly south of I-96 Monday evening with light snow
accumulations.

More significant/impactful winter wx will develop late Monday
night through Tuesday due to brisk nw flow caa behind the arctic
cold front. It will become windy late Monday night into Tuesday
with falling temperatures through this time frame.

NW flow lake effect snow bands will develop late Monday night and
continue through Tuesday as h8 temps plummet to -16 to -18 C by
12Z Tue. This will yield delta t/s in the lower to middle 20`s and
very strong lake induced instability. Les should be most prolific
from early Tuesday morning through Tuesday evening when inversion
heights near Lake MI will reach 9-10 kft.

We expect around 4 to 8 inches of snow in our favored nw flow snow
belt regions near to mainly west of US-131 from very late Monday
night through Tuesday night. Isolated locally higher amounts near or
even in excess of ten inches are possible where the les bands are
most persistent.

Some sort of winter weather headline will eventually be needed for
this event for those areas. Further inland snow accumulations will
be significantly less. Thanks for extensive coord on the no headline
decisions at this time APX/DTX/IWX.

.LONG TERM...(Wednesday through Sunday)
Issued at 330 PM EST Sun Dec 10 2017

Models are not in good agreement regarding the track and timing of
the next clipper system, so will side with the ECMWF (operational
and ensemble mean) which shows it passing south of the state on
Wednesday night.

This track, from roughly Des Moines to Cincinnati, leads to an
easterly low level flow that shuts off the lake effect. Also the
synoptic snow related to this feature would likely pass mostly just
south of Michigan, so Wednesday into early Thursday could
potentially end up being a quiet period.

Guidance is in decent agreement showing westerly low level flow
resuming later Thursday into Friday as a large sfc high slides east
across the srn U.S. and a low forms north of Lake Huron. This should
get lake effect snow showers going again, which could work in
concert briefly late Friday/Friday night with a warm advection
pattern ahead of an approaching warm front.

We get a break from the cold next weekend. Medium range guidance has
been consistently advertising a temporary shift from the amplified
pattern aloft (deep trough) to a flatter/more west-east flow of
pacific origin. High temps may reach 40 degrees next weekend with
the primary precip risk probably lifting north of our area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1247 AM EST Mon Dec 11 2017

This forecast will be an unsettled period with a couple of periods
of impactful conditions with snow, lower conditions, and
eventually wind.

Conditions are relatively tranquil to start out the period. All
sites have seen cigs lift above 3k ft for VFR conditions. This
will continue likely through 12z.

A narrow band of snow will then approach from the West after 13z.
This will likely only impact each of the terminals for 2-3 hrs.
When it does come through, IFR will be likely for a short period
in vsbys and cigs. This will move East then, and a lull in the
activity can be expected with only light pcpn.

We then expect a band of convective snow to develop across the
area, especially along I-96 after about 20-21z from West to East.
The biggest impacts will be near the I-96 corridor where LIFR/
VLIFR will be likely under the band. The I-94 terminals will see
some snow, but it will likely not be as intense as up North. This
will last almost through the end of the period as the low moves
by. When the snow lightens up, winds will increase with gusts over
20 knots toward the end of the period.

&&

.MARINE...
Issued at 330 PM EST Sun Dec 10 2017

A small craft advisory remains in effect through late tonight. In
addition we will hoist a gale watch for late Monday night through
early Tuesday afternoon when wind speeds will likely reach gale
force.


&&

.HYDROLOGY...
Issued at 1000 AM EST Sun Dec 10 2017

Rivers are running near normal levels to a little above normal. No
flooding or significant rises in river levels are expected. Snow is
forecast periodically through the week.

Temperatures have been near to below freezing since last Tuesday
night and similar temperatures are expected to persist through the
end of this week. This should allow ice to begin forming on area
rivers, especially on the Muskegon River in Central Lower
Michigan.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Gale Watch from this evening through Tuesday afternoon for
     LMZ844>849.

     Small Craft Advisory until 1 AM EST early this morning for
     LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Meade
AVIATION...NJJ
HYDROLOGY...63
MARINE...Laurens


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