Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 030458
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1158 PM EST Fri Dec 2 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 314 PM EST Fri Dec 2 2016

Quiet weather with little impact can be expected through Saturday
night. Just a lot of cloud cover expected with a chance of a
sprinkle or flurry on Saturday. Temperatures will remain near
seasonal levels.

The area will see a weak system move through the area Sunday and
Sunday night. This is expected to bring some light snow to the area
from late Sunday morning through Sunday evening, before changing
over to drizzle or freezing drizzle Sunday night.

Low chances of precipitation can be expected for the early portion
of next week. We will see colder air move in for the end of next
week with some snow. Lake effect could kick in fairly well late next
week.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 314 PM EST Fri Dec 2 2016

Our main focus is on the latter portion of the fcst period where
some accumulating snow will be possible across most of the area.
Until then, fairly quiet weather is expected.

The radar for SW Lower MI is very quiet this afternoon. A band of
light showers with a weak short wave moved through earlier, and has
since slipped south of the CWFA. In it`s wake, inversion heights
have dropped and the DGZ has become unsaturated. Lake effect clouds
will be the main feature. The cloud cover will keep temps from
dropping too much tonight.

We should remain mostly dry on Sat, but can not rule out a few
flurries and/or sprinkles in the afternoon hours. We see a slight
increase of the moisture layer on Sat that will come close to
touching the DGZ. This occurs as an upper shear zone to our SW lifts
NE toward the area. Temps should be above freezing once again, so
nothing to be concerned about with this.

We will see light snow spread in from the west across the area late
Sunday morning through Sunday afternoon. We will see a couple of
short waves in the nrn stream phase over the Plains before moving
into the Great Lakes region. Good warm and moist advection aloft
ahead of the upper wave going negative tilt will supply the forcing
for this event.

Amounts generally still look to be around an inch or two with this
event, especially on the grassy areas. temps look like they should
be around or just above freezing for most of this event. This will
limit the impacts on the road to where local snow rates might
briefly become a little better. Areas near the lake might see less
with a little warmer sfc temps.

The snow should transition to some light drizzle or freezing drizzle
Sunday evening as the deep moisture is lost, but low level moisture
and lift remains. Model consensus is that temps will likely rise a
tad behind the snow and remain freezing. There is a chance temps
could remain a little cooler due to fresh snow. With this in mind,
we have a mention of drizzle or freezing drizzle Sunday night.

.LONG TERM...(Monday through Friday)
Issued at 314 PM EST Fri Dec 2 2016

A shot of colder air is still poised to arrive by the middle of next
week along with lake effect snow showers. Some questions remain
about the exact timing and degree of the colder air and whether we
will largely stay dry Monday through Wednesday until this colder air
arrives.

Initial concerns center on precip chances on Tuesday. An upper low
across Mexico will traverse Texas on Monday and help reinvigorate
Gulf flow into the southeast U.S. Sfc low development between the
GFS and ECMWF is more agreed upon with the 12z runs as this storm
system looks likely to track near the Ohio Valley region and largely
miss our area. Pops are still warranted especially near/east of I-69
to account for precip on the far NW edge of this system. Rain looks
like the predominant type but snow may mix in as well. Some wobbles
in storm track are possible of course, but secondary low development
off the Carolinas may preclude a more northward track of this low
toward the Great Lakes. It is noted that the GEM is slower and a bit
further NW but the solution is questionable given the low
development off Carolina and where the H500 shortwave trough is
located.

The GFS is still quicker than the ECMWF and GEM with when the
-15C air at H850 arrives. In fact, it is at least 24 hours quicker.
Looking at the H500 longwave pattern, the GFS simply has the large
upper low more expansive and further south than either the ECMWF or
GEM. This has implications on when the lake effect gets going and
which commutes next week will be impacted by snow. The target window
for any significant lake effect will either be centered on the
Wednesday-Thursday time frame (GFS) or Thursday-Friday (ECMWF)
depending on which model solution verifies.

At any rate, at least Thursday looks like a wintry day for WNW flow
areas including Muskegon...Grand Rapids...and Holland. The DGZ is
saturated (with lift) and the column may potentially become deeply
saturated (up to H500 or higher) Thursday night and Friday which
would occur as WNW winds likely turn NW. Boundary layer winds of 20-
30 kts should not be high enough to shear the bands apart
(minimizing accums), so organization of bands may occur. Several
inches of snow look possible at this early stage for the favored
WNW/NW flow areas for the duration of the event.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1125 PM EST Fri Dec 2 2016

Mvfr conditions will continue overnight through much of Saturday
due to extensive low cloud cover. A few snow flurries may develop
Saturday morning into early Saturday afternoon mainly at our
western terminals (KMKG... KAZO and KGRR). Conditions will
gradually improve to vfr Saturday afternoon through Saturday
evening as ceilings improve. Winds will remain westerly at around
5-10 kts through the next 24 hrs.

&&

.MARINE...
Issued at 314 PM EST Fri Dec 2 2016

We will be cancelling the Small Craft Advisory just a little early
this afternoon. Conditions seem to have quieted down enough per the
mid-lake buoy and coastal web cams along the shore.

Most of the weekend can be expected to have conditions below
advisory conditions. Winds aloft will come up late Sunday, but will
likely not be realized at the surface. The next best chance for
advisory conditions would be toward Tuesday night.


&&

.HYDROLOGY...
Issued at 314 PM EST Fri Dec 2 2016

The Maple River continues its slow climb toward bankfull, and may
reach that stage by early next week. A tenth to quarter inch of
liquid equivalent precip, in the form of snow for much of the area,
is expected late Sunday. Additional chances for precipitation will
arrive the latter part of next week, most likely in the form of lake
effect snow. This moisture should have little impact on rivers in
the short term.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Hoving
AVIATION...Laurens
HYDROLOGY...CAS
MARINE...NJJ


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