Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 140830
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EST Thu Dec 14 2017

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

.SYNOPSIS...
Issued at 330 AM EST Thu Dec 14 2017

A wintry pattern will continue across Lower Michigan the next couple
of days. Highs are expected to be below freezing Thursday through
Saturday with potential for additional snow. The snow is not
expected to be heavy, but late tonight into Friday accumulations are
likely once again. A trough of low pressure will swing through the
area during the Thursday night and Friday time frame which will
enhance some lake effect snow. Accumulations of 2 to 3 inches are
possible with the Friday morning commute affected by snow.

&&

.SHORT TERM...(Today through Saturday)
Issued at 330 AM EST Thu Dec 14 2017

Focus in the short term is on the potential for some accumulating
snow Thursday night into Friday. Some additional snow is expected
Friday night into Saturday.

Today, we will see a band of snow that is mainly off shore this
morning move into western portions of Lower Michigan. Not expecting
much in the way of impact from this band, but an increase in clouds
and some snow showers are expected. Some light accumulations of an
inch or less are possible especially up towards Big and Little Sable
Points.

Tonight an upper shortwave and assoicated surface trough will
approach Lake Michigan from the west. Expecting an increase in
coverage and intensity of lake effect snow around 11 PM.
Accumulating snow is possible shortly thereafter with the NAMnest
and HRW NMMB both showing big boosts to an area of lake enhanced
snow overnight. The western two tiers of counties in our CWA will be
most affected. The snow will continue into Friday morning, before
tapering off some into Friday afternoon. Thinking 1 to 3 inch
amounts will be fairly common and cannot rule out some localized 4
inch totals. The Friday morning commute will be affected to some
degree by falling snow. Some blowing snow is certainly possible
towards the lakeshore as well, given an increase in westerly winds
around that time to 10-20 mph with higher gusts. Holding off on an
advisory at this point as we are not confident enough that impacts
will rise to the level at this point.

A band of warm air advection snow looks possible for Friday night
into Saturday morning. Good lift is noted on the 290K surface during
this time frame moving from south to north through the forecast
area. Accumulations with this band should be on the light side.
Around an inch certainly looks possible though.

.LONG TERM...(Saturday night through Wednesday)
Issued at 330 AM EST Thu Dec 14 2017

A quieter period with temps returning to near normal values is
expected for the weekend and lasting into early next week.  Then we
should turn colder again Tuesday and Wednesday with snow returning.

The upper flow becomes more zonal leading to temps bouncing up to
normal readings of the mid and upper 30s for Sunday and Monday.  A
quick moving front comes through Sunday afternoon which should bring
scattered rain and snow showers.  But given the quick movement, it
should produce little impact.  It appears we will have a quiet
period from Sunday night through Monday night as we should be in
between systems.

An upper trough and surface cold front passes through late Monday
night into Tuesday. This will bring back the cold as temps should
fall on Tuesday.  H8 temps trend back toward -10C which will be cold
enough to bring lake effect snows back to the forecast.  These
probably start Tuesday afternoon and continue through Wednesday
morning.  The set up looks good for accums in a WNW flow.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1210 AM EST Thu Dec 14 2017

The snow was exiting the region as of 05Z. Some lingering MVFR
ceilings will hold through about 08Z toward JXN/LAN, then a period
of VFR will move in with clearing skies.

Winds will pivot from the north to the northwest allowing some
lake effect to return after about 14Z. This will impact AZO, MKG,
GRR and BTL with occasional, mainly light snow showers with MVFR
and patchy IFR.

A better slug of moisture will arrive late in this TAF period,
toward 02Z, when the snowfall will increase once again. Expect
the IFR to become more commonplace, especially toward the usual
snow belts with a westerly flow.

&&

.MARINE...
Issued at 330 AM EST Thu Dec 14 2017

Maintained the current Small Craft Advisory which is in effect
through 11 AM this morning. Wind gusts from the Muskegon and
Saugatuck piers have been between 20-30 knots much of the last 12
hours. Given this type of wind, expect waves of 3 to 5 feet in the
nearshore waters. The wind goes lighter for a time this morning and
the wave field should dampen out as we had to midday, to at least
below advisory threshold.

The next Small Craft Advisory potential comes quickly on the heels
of the current one with westerly flow increasing tonight into
Friday. We will likely need another SCA starting tonight roughly
around midnight stretching into Friday night. West winds are
forecast to reach the 15-30 knot range which will build waves into
the 5 to 8 foot range.

&&

.HYDROLOGY...
Issued at 329 PM EST Wed Dec 13 2017

Snow and cold temperatures the next few days will promote ice
development on rivers. Some river gauges will likely become affected
by ice and produce spurious readings. Freeze up ice jams are
possible and could produce minor upstream rises, but flooding is not
anticipated. Above-freezing temperatures are expected on Sunday.
Snowpack water equivalents across much of the area range between a
quarter to half inch, but a full snowmelt is not expected any time
soon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 11 AM EST this morning for
LMZ844>849.

&&

$$

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



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