Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 091755
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1255 PM 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.

&&

.UPDATE...
Issued at 1135 AM EST Sat Dec 9 2017

The winter wx advisory has been cancelled for all but Van Buren
county where the advisory remains in effect until 7 pm.
Accumulating snow has ended across the vast majority of our fcst
area and any lingering light snow showers and flurries will
continue to gradually taper off this afternoon.

The exception to this is in Van Buren county for a northerly flow
les band will continue to affect mainly western Van Buren county
where additional snow accumulations of an inch or two are still
possible mainly west of Paw Paw this afternoon. Therefore the
winter wx advisory remains in effect for Van Buren county until 7
pm.

&&

.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1255 PM EST Sat Dec 9 2017

Still some lingering IFR vsbys in light snow over the next couple
hours otherwise widespread MVFR cigs this afternoon trending
toward predominately VFR conditions by 00Z as snow system departs.

Lake effect snow bands will be offshore this afternoon due to
northerly wind direction. However tonight the winds become more
westerly which will drive the snow showers back inland. So
conditions should trend back to MVFR from GRR/BTL westward
tonight, with even some IFR vsbys possible for a few hours at MKG
and AZO as they come onshore shortly after 00Z.

Westerly flow supports more lake effect snow showers on Sunday,
some of which could occasionally produce MVFR or perhaps even IFR
vsbys, mainly along the I-96 corridor from MKG to GRR to LAN.

&&

.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 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...Winter Weather Advisory until 7 PM EST this evening for MIZ071.

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

&&

$$

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



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