Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 062030
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EST Wed Dec 6 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine/Hydro

.SYNOPSIS...
Issued at 329 PM EST Wed Dec 6 2017

A period of lake effect snow will continue through tonight and
Thursday. Areas along and west of U.S. 131 will see 2 to 4 inches
with locally higher amounts.  Meanwhile areas east of U.S. 131 will
see two inches or less.  We will see a brief lull in the snow
Thursday night.  Then more lake effect snow kicks back up on Friday,
mainly from Holland north and west of U.S. 131.  All areas will see
snow by late Friday night as a clipper system moves in.  Once again
the heaviest snows can be expected from U.S. 131 westward, while a
more widespread snow can be expected to the east too.  The snow will
wind down on Saturday, then more solid snow chances return Monday
night through Tuesday night.

Temperatures will remain chilly with daytime highs mainly in the
upper 20s to mid 30s.  Lows will mainly be in the 20s into the
middle of next week.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 329 PM EST Wed Dec 6 2017

A WNW flow lake effect will impact the CWA tonight and Thursday.
Then more lake effect, with a WSW flow, is expected Friday into
Friday night.  This will occur ahead of a strong clipper system that
will increase the snow across all of the CWA late Friday night.

Will not change any of the winter headlines at this time.  We will
need watch how the bands set up over the SW CWA as it is possible we
will need to add Barry and Calhoun Counties to the advisory.  With a
285-310 flow through the event the more intense bands crossing the
widest part of the lake could also spill into these two counties.

Inversion heights continue to lift tonight and the lake effect will
continue to increase.  The peak snowfall intensity will probably be
occurring during the morning rush on Thursday.  The first
significant snow during a rush hour certainly raises concerns. After
a morning peak in the moisture, it begins to lessen through
Thursday, likely resulting in diminishing snows through the
afternoon.  All in all, expect 2 to 4 inches across much of the
lakeshore counties and localized more.  A bulge inland is expected
across Lake and Kalamazoo Counties, and as mentioned above, perhaps
Barry and Calhoun Counties.  Away from these counties accums are
expected to be 2 inches or less.  Breezy winds will cause some
drifting snow.

The short wave crosses the region mid day Thursday which will lead
to a lull in the snow Thu night.  But then the moisture depth
increases again on Friday when inversion heights of 6-7k feet move
in.  The flow in this time frame is more WSW ahead of an approaching
clipper.  1 to 2 inches seems the likely snow accums range, with
locally higher amounts.  This mainly falls north of Holland and west
of U.S. 131.  Once again it will be breezy, so some drifting is
expected.

The clipper system continues to look impressive and will likely need
winter headlines.  It moves in late Friday night.  Lake enhanced
snow will continue and could become quite heavy.  Given a synoptic
system, inland areas will also see a more widespread snow too.  At
this point an additional 2 to 5 inch snowfall appears likely,
heaviest toward the lakeshore.  However these types of systems will
over perform at times.  Winds lighten up overnight so drifting is
not expected.

.LONG TERM...(Saturday through Wednesday)
Issued at 329 PM EST Wed Dec 6 2017

Bouts of lake effect snow are expected through the long term period
as the deep upper trough remains across the eastern half of the
country. Lake effect will be boosted on Saturday via a low pressure
system diving southeast through the Great Lakes region. Most areas
on Saturday will see an inch or two of snow via the low. Lakeshore
counties will see even more given a lake enhanced snow regime.
Southwest flow will turn northwest through the course of Saturday
making accumulations likely in all areas towards the lake. Lake
effect snow events that are enhanced via synoptic systems can be
some of the more impactful snow we see, so traveling on Saturday
will need to be monitored.

A lull in the snow activity will occur on Sunday as ridging moves
through the area. A nose of warm air on Sunday and Sunday night may
actually take lake effect snow out of the equation for a time as
delta t`s dwindle near or below critical values.

A cold front will drop through the area on Monday ushering in cold
air and another round of northwest flow lake effect. The lake effect
will last into Tuesday and Wednesday.

After a delayed start to this wintry pattern at least in the
Southern Great Lakes, we should see most areas covered in snow by
early next week. Temperatures much of the long term will be below
normal, the exception being Sunday into Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 111 PM EST Wed Dec 6 2017

Winds will remain gusty and fairly strong through about 00z, with
sustained winds of 15-20 knots and gusts over 30 knots at times.
Winds will taper to 7-10 knots tonight after roughly 00z.

Lake effect snow will develop as we work through the next 12-18
hours. Aviation conditions will deteriorate tonight as MVFR
ceilings become more widespread. Visibilities will dip into the
MVFR category at KMKG, KGRR and KAZO with IFR possible as well due
to snow showers. Lake effect snow will reach a peak late tonight
and tomorrow morning between 09z and 15z on Thursday.

&&

.MARINE...
Issued at 329 PM EST Wed Dec 6 2017

Small craft advisory will be in affect at least through Friday given
the brisk westerly winds.

&&

.HYDROLOGY...
Issued at 329 PM EST Wed Dec 6 2017

Several rounds of snow are expected over the next week due to a
combination of lake effect processes and passing low pressure
systems. The first round of more widespread snow will occur late
today through Thursday afternoon, bringing several inches of snow to
counties near the lakeshore. Total liquid equivalent (melted snow)
through Thursday evening will be below one-quarter of an inch for
most locations, but locations in Allegan, Van Buren, and Kalamazoo
counties could see locally higher totals up to one-half inch. No
issues with flooding or rivers are expected. Another round of more
widespread snow is expected to start mid-day Friday and last through
Saturday afternoon. This looks to bring another tenth to one-quarter
of an inch of liquid equivalent, and again not cause any issues
aside from accumulating snowfall.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 4 PM EST Thursday for MIZ037-038-
     043-050-056-064-071-072.

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

&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Duke
AVIATION...Duke
HYDROLOGY...HLO
MARINE...JK



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