Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 102334
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
634 PM EST Sun Dec 10 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.

&&

.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 00Z TAFS through 00Z Monday evening)
Issued at 630 PM EST Sun Dec 10 2017

Light precipitation was occurring along a front tracking
southeastward through the TAF sites. Some of this was in the form
of freezing drizzle. The front pushes through KJXN by 03z. A few
snow showers with local impacts may persist along the lakeshore
tonight...otherwise VFR weather should develop and then persist
through the night

Another wave of low pressure arrives for Monday...with IFR and
lower impacts expected to develop during the day.

&&

.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 Monday evening through Tuesday afternoon for
     LMZ844>849.

     Small Craft Advisory until 1 AM EST Monday for LMZ844>849.

&&

$$

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



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