Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 092347
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
647 PM EST Sat Dec 9 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 PM EST Sat Dec 9 2017

A few light snow showers and flurries are forecast through the
rest of the weekend. The next clipper system will bring another
round of accumulating snow Monday through Monday night. The
coldest airmass of the season thus far will move in Tuesday and
Wednesday with lake effect snow showers.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 325 PM EST Sat Dec 9 2017

A band of light deformation zone snow from near Holland ne to Mt.
Pleasant will continue to sink slowly south late this afternoon and
bring nothing more than a dusting of snow. Light lake effect snow
showers will affect areas near to mainly west of US-131 this evening
as low level winds back to the northwest. This will allow the north
to south oriented dominant lake effect snow band over eastern Lake
MI to drift inland a bit.

However this les band will diminish considerably as it drifts inland
tonight and inversion heights crash. Elsewhere only a few flurries
are expected overnight and partial clearing will develop.

Very light westerly flow lake effect snow showers and flurries are
expected Sunday but with very little (less than an inch) snow
accumulation. An upper level disturbance moving in from the nw will
also bring some light snow showers Sunday afternoon.

An Alberta clipper will bring snow Monday through Monday night.
The snow will develop from nw to se across our fcst area Monday
morning as suggested by latest sref guidance pops and then
continue through the afternoon into the evening.

The event will morph from a synoptic event to a lake effect event
Monday night as brisk northwest flow caa occurs on the back side
of the departing clipper. The synoptic snow will affect travel
Monday and travel Monday night will continue to be affected by nw
flow les, windy conditions and falling temperatures. We expect two
to four inches of snow Monday through Monday night with isolated
locally higher amounts to near six inches possible due to lake
enhancement.

.LONG TERM...(Tuesday through Saturday)
Issued at 325 PM EST Sat Dec 9 2017

Additional impacts from lake effect snow are likely on Tuesday and
Tuesday evening near and west of Highway 131 due to brisk northwest
flow on the back side of the departing clipper system.

Much colder boundary layer air than what we are currently seeing
should lead to a higher potential for blowing snow and icy road
conditions Tuesday due to a more powdery type snow.  If inland areas
manage to clear on Tuesday night, low temps could fall to around
zero in spots.

Intensity of lake effect snow is expected to decrease for later
Tuesday night into Wednesday as a period of surface ridging and
lower inversion heights comes through.

Confidence lowers beyond midweek regarding timing of better periods
of lake enhancement, but a southwest flow event appears possible for
Wednesday night into Thursday as next sfc low tracks across northern
Michigan. This would focus best accumulations from Holland and GRR
northward, before winds shift northwesterly again later Thursday
into Friday.

Temperatures are expected to moderate into the mid to upper 30s next
weekend, providing a temporary but short lived break to lake effect
snows before colder air returns again the following week of 17Dec.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 647 PM EST Sat Dec 9 2017

A snow squall will bring some IFR conditions along the Lake
Michigan coast early this evening then move inland with some MVFR
conditions at AZO and GRR by midnight. Periods of light lake
effect snow can be expected on Sunday with VFR prevailing most of
time.

&&

.MARINE...
Issued at 325 PM EST Sat Dec 9 2017

The small craft advisory remains in effect through late Sunday
night. Waves will finally subside a bit early Monday before
quickly ramping back up again later in the day.

&&

.HYDROLOGY...
Issued at 1030 AM EST Sat Dec 9 2017

Rivers are running near or a little above normal. No flooding or
significant rises in river levels are expected. Accumulating snow is
expected today and again late Sunday through Tuesday.

Temperatures have been near to below freezing since Tuesday night and
similar temperatures are expected to persist through the end of next
week. This should allow ice to begin forming on area rivers.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 1 AM EST Monday for LMZ844>849.

&&

$$

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



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