Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 070233
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
933 PM EST Tue Dec 6 2016

LATEST UPDATE...
Update

Took out the pops for this evening. Colder air is beginning to
move over the lake and a chance remains that a few shsn could
develop overnight.

The blast of cold air for later in the week still is on track and
so no changes to the winter storm watch along the lake shore.

.SYNOPSIS...
Issued at 301 PM EST Tue Dec 6 2016

We will see winter weather conditions develop across the area,
especially overnight Wednesday night and Thursday. Lake effect snow
showers will increase in coverage and intensity, especially across
Southwest Lower and Northwest Lower Michigan. Snow will become
locally moderate to heavy at times, with some blowing and drifting
snow. These conditions will linger into Friday, before gradually
tapering off

Another system could move in late Saturday and last through Sunday.
This would bring another round of snow to the entire area. Colder
temperatures will remain in place through the weekend.

&&

.UPDATE...
Issued at 931 PM EST Tue Dec 6 2016

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 301 PM EST Tue Dec 6 2016

We have issued a Winter Storm Watch for the NW and SW corners of the
CWFA for the period from late Wednesday night through Friday. This
is for the potential of locally heavy snow accumulations and some
blowing and drifting snow.

Fairly quiet weather through Wednesday evening, but we will be
seeing a trend toward the snow showers picking up. There could be a
few brief light rain/snow showers up north with the nrn stream
system that will generally stay north of the area. The srn
stream system has shifted east of the area, and will not directly
affect our area. Any pcpn will change over to snow showers later
this evening and overnight as some cooler air starts to move in.

There will be a few snow showers Wed and Wed evening, mainly across
the wrn half of the area. We will see moisture depth increase some,
and the dgz will become saturated overnight. It will still remain
limited below 5k ft, as the area will remain on the anti-cyclonic
side of the upper jet. This will limit the low level convergence.
Over lake instability will become very sufficient, increasing to
around the upper teens C.

The snow showers are expected to pick up significantly after
midnight Wednesday night. This occurs as the upper jet sinks south
of the state after 06z. Moisture will increase to over 10k feet, and
the low level convergence picks up significantly as a result.
Overlake instability climbs to over 20c. The mean low level flow
will initially be wrly, which favors the wrn half of the cwfa
through Thu. It will then shift to more NW Thu evening and last
through Fri when the upper jet lifts north of the area. This will
favor the NW and SW corners of the area.

We expect that the watch area will see the biggest impacts, and the
most snow given the flow evolution through the entire period. We
expect that additional advisories will be needed to buffer the watch
area as we approach the event. The fine details can be ironed out in
subsequent forecasts.

.LONG TERM...(Friday through Tuesday)
Issued at 301 PM EST Tue Dec 6 2016

There are several impactful events forecasted in the long term
period.

To start the first event will be winding down on Friday. The low
level flow will be northwest...which favors areas generally north of
Muskegon and south of Holland for the heaviest snow. The morning
commute looks rather impacted with bands of lake effect snow
ongoing...some of which will be heavy. During the afternoon the
moisture depth is shown to drop off...which should support a
diminishing trend to the snow.  The pressure gradient weakens during
the day so the morning looks gustier than the afternoon.

Much less in the way of snow is expected Friday night into Saturday.
Then Saturday afternoon or evening the flow backs to the south and
the temperature profile will be favorable for lake enhanced
moisture.  So with a synoptic wave moving and combining with lake
enhanced moisture...areas along and west of highway 131...especially
north of Holland should be favored for an impactful event.  Will
need to monitor trends closely in the coming days.

Yet another wave could arrive for early next week...with arctic air
settling in behind it.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 631 PM EST Tue Dec 6 2016

A weak cold front is moving across the state attm and will act to
scour out the mvfr cigs this evening. We expect cigs to become vfr
by mid evening.


&&

.MARINE...
Issued at 301 PM EST Tue Dec 6 2016

We have extended the Small Craft Advisory another period, to match
the length of the nearshore forecast. The gradient will remain tight
through that time, with very unstable conditions as the colder air
moves in. We could approach gales at times, but most likely will
remain under that with the winds expected in the mixed layer.


&&

.HYDROLOGY...
Issued at 1156 AM EST Tue Dec 6 2016

Near and above normal river levels continue to affect southwest
Lower Michigan today. The Looking Glass River at Eagle shows
notable rises, but should remain within banks. Slight rises have
also been noted on the Maple River at Maple Rapids, as expected.

Moist soils will provide opportunity for runoff with additional
precipitation this week. Lake effect snow will distribute most of
the precipitation to lake shore counties this week. The weekend
will feature more of a synoptic setup to provide inland locations
with precipitation. Overall, while high rivers may be a concern,
none of the precipitation is too heavy for any given site or
individual episode. Therefore, river rises are possible, but
flooding is of low concern at this time.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Watch from late Wednesday night through Friday
     afternoon for MIZ037-038-043-056-064-071-072.

LM...Small Craft Advisory until 7 PM EST Thursday for LMZ844>849.

&&

$$

UPDATE...04
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...04
HYDROLOGY...JAM
MARINE...NJJ



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