Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 091143
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
643 AM EST Sat Dec 9 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 320 AM EST Sat Dec 9 2017

Snow will be widespread across the area this morning as a
developing storm system, over central Lake Michigan at sunrise
moves to Lake Ontario by this evening. Lake shore area will see
as much as 5 to 8 inches of snow by late this afternoon, inland
only an inch or two of snow is expected. Tonight and Sunday expect
only flurries with continued cold temperatures as a high pressure
system passes to the south of Michigan. The next storm system
moves through the area Monday with additional snowfall across the
area. That will be followed by the coldest air of the season so
far for Tuesday and Wednesday. During that time expect snow
showers near Lake Michigan but partly cloudy skies inland.

&&

.SHORT TERM...(Today through Monday)
Issued at 320 AM EST Sat Dec 9 2017

Our main concern this morning is the winter weather headlines and
just where the heaviest snowfall will actually be. In fact I
extended the Winter Weather Advisory for Ottawa, Kent, Muskegon,
Ocean and Mason till noon since the snow will likely linger longer
than previously through. Even so the system is tracking as
forecast. However the area of heaviest snowfall this morning
seems a touch farther north then I was expecting. The best lift
and low level convergence will be over Ottawa and Muskegon
counties till mid morning. That is where the low level inflow
intersects the lake shore. As the upper wave continues to dig
south southeast helped by a 140 knot 300 mb jet core over
Wisconsin early this morning. The area of enhanced snowfall will
then sink south to Allegan and Van Buren Counties this afternoon.
So that headline will remain as is. I expect storm total snowfall
will be in the 5 to 8 inch range.

Tonight the upper wave moves out and inversion height crash to
near 5000 ft so any significant snowfall should end. Skies may
even clear for a time inland of US-131. Winds become westerly on
Sunday as a system passes off to our north. This will bring clouds
inland and maybe a few flurries (inversion heights are to shallow
for significant snowfall).

The next system, which is a clipper low, that dives south
southeast from central Canada toward southern Lower Michigan on
Monday. Seems the track will be similar to todays system and it
may have similar results too. So expect measurable snow over most
of the CWA on Monday.

.LONG TERM...(Monday night through Friday)
Issued at 320 AM EST Sat Dec 9 2017

More colder than average temperatures and occasional snow showers
sums up the long term fairly well. There is some indication that we
may warm up to around average toward the end of the long term, or
just beyond.

We will be dealing with another clipper system at the beginning of
the long term on Mon evening that will bring another shot of snow to
the area. The models are coming to a consensus with regards to the
track of the low. The consensus takes the low across Southern Lower.
This will bring a shot of snow to the entire area. Some enhancement
will be likely ahead of the system with a southerly component to the
wind. A transition to lake effect can then be expected behind the
system as the colder air will be reinforced with a NW flow.

We will likely see a break in the accumulating lake effect toward
Wed as sfc ridging moves across the area with short wave ridging
aloft moving through. This will potentially be short lived as the
next clipper type system will be poised to move through the region.
Again models differ on this system, as they have with the Mon/Mon
night system. It will at least keep a threat of more snow showers,
with details (amounts, lake enhancement, etc...) yet to be
determined. More lake effect can be expected in the wake of this
system also with more cold air pouring in.

We will see a diminishing trend in the snow showers on Fri as
another ridge moves through. We could be looking at a moderating
trend beginning as early as Fri, and more likely after the long
term. This occurs as there is indication that this strongly
amplified upper air pattern (ridge west, trough east) will flatten
out a bit to a more zonal pattern as a strong Pacific jet helps to
beat the western ridge down a bit.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 644 AM EST Sat Dec 9 2017

The bands of snow around the developing system have significantly
intensified during the past hour or so. MKG has been 1/4SM V 1/2SM
VV007 between 10z and 11z. A heavy snow band is about to move into
the GRR taf site (by 1215z or so). This entire area of snow will
move slowly east this morning brining IFR /LIFR to most of the TAF
sites through 16z or so. After that the system will have moved
southeast to near AZO. So that should bring in some drier air from
the north ending the snow from west to east. However due to Lake
Michigan there will be a North/South snow band off shore this
morning that will march across western lower Michigan before
dissipating in the 00z to 06z time frame. So MKG and maybe GRR and
AZO may get another 2 to 4 hours of snow showers when that moves
through. After that just MVFR cigs through sunrise Sunday.

&&

.MARINE...
Issued at 320 AM EST Sat Dec 9 2017

I continued the Small Craft headlines until midnight Sunday night,
as winds and waves will continue to meet criteria till then.
Little question the gale force winds will remain outside of our
Near Shore area today.


&&

.HYDROLOGY...
Issued at 113 PM EST Fri Dec 8 2017

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

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

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 7 PM EST this evening for MIZ064-
     071.

     Winter Weather Advisory until noon EST today for MIZ037-043-050-
     056-057.

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

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...63
MARINE...WDM


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