Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 151615

Area Forecast Discussion
National Weather Service Grand Rapids MI
1115 AM EST Fri Dec 15 2017


Issued at 330 AM EST Fri Dec 15 2017

A burst of lake effect snow is expected this morning. The increase
in intensity of the snow is due to an upper level disturbance
swinging across Lake Michigan. Through the course of the afternoon
the snow should wind down. For a time this morning though, travel
conditions will be poor with limited visibility and slippery roads.
The peak in the snow will be right around the morning commute in
most areas. Snowfall should range from 1 to 3 inches for areas along
and west of U.S. Highway 131 and an inch or less to the east. Some
additional light snow is possible tonight into Saturday as a
weakening warm front moves our way. A weakening low may bring us
some rain and snow on Sunday as warmer air will have moved into the
region from the south. Highs will remain in the 20s again today, but
by Sunday we should be well into the 30s.


Issued at 1115 AM EST Fri Dec 15 2017

No real adjustments needed to the fcst this morning as things are
pretty much on track with the snow this morning. We will hold on
to the advisory into the afternoon to allow the snow showers to
trend down more before allowing it to expire.

The expected burst of snow has pretty much evolved as expected
this morning, with moderate to locally heavy bursts occurring. The
heavier snow showers are shifting to the S and E as the short wave
works through the area. We continue to expect a downturn in the
snow showers this afternoon as subsidence builds in the wake of
the short wave.

It will not come to a complete end, especially down south as the
sfc cold front hangs up down there and warm air advection begins
over the front. Amounts are not expected to be significant from
now and beyond. An additional inch or two will be possible.


.SHORT TERM...(Today through Sunday)
Issued at 330 AM EST Fri Dec 15 2017

Focus in the short term is on three items... 1) a lake enhanced snow
event today, 2) the potential for a little warm air advection snow
tonight into Saturday and 3) a weakening low bringing precipitation
chances on Sunday.

The lake enhanced snow event today remains on track and made no
changes to the going Winter Weather Advisory. If there is a trend in
the models from last night into tonight, it looks like snow totals
may be just a tad lower. 1 to 3 inches looks like it should cover
the bulk of the snow. The max in the event should be between now and
about 11am or so. The upper shortwave is seen in water vapor imagery
over Northern Wisconsin moving quickly toward Central Lake Michigan.
This shortwave will give a boost to the lake effect snow through an
increasing depth of moisture and synoptic scale lift added to the
convective boundary layer. 925-850mb layer omega details why snow
totals will be held in check, which is the fact that the good lift
will be transitory across the western CWA. It is not sustained for
more than a few hours at any one location. Still, thinking impacts
can be expected as heavier snow bursts slicken up the roads right
around the time of the morning commute. The snow should wind down
this afternoon from west to east.

Tonight into Saturday a band of warm air advection snow will move
into the forecast area from the south. Trends have been for lesser
amounts to the snow. The weakening trend is due to the fact that the
low responsible for the warm air advection is filling with time as
it moves our direction. Thinking snowfall via this band will be an
inch or less.

On Sunday a surface low moves our direction from the south. The
upper shortwave associated with the low is moving into confluent
flow aloft and it is weakening with time. Have some rain and snow
showers in the forecast for Sunday afternoon, but model trends have
been for a weaker low and less in the way of precipitation. Impacts
should be nil as temperatures will be above freezing.

Most impactful weather in the short term will come this morning.
High temperatures will moderate some each day, with highs above
freezing in all areas by Sunday.

.LONG TERM...(Sunday night through Thursday)
Issued at 330 AM EST Fri Dec 15 2017

Relatively quiet to start the week as the flow remains zonal and we
will have a soft southerly flow.  Sunday night and Monday may see
some areas of fog and patchy drizzle, otherwise temps will be near
to slightly above normal.  Light warm advection rain showers may
occur ahead of a cold front Monday night that may mix with snow
across Central Lower.  We will have to watch to see if the cold
shallow air is completely scoured out, since some light freezing
rain could also occur across the interior north.

We should be brushed by colder air in the Tue/Wed time frame behind
the departing front and we briefly get into upper troughiness. Still
looks cold enough for a quick shot of lake effect snows mainly
Tuesday afternoon and evening.

Model differences arise toward the end of the forecast period.  But
it does appear solid warm advection returns by Wednesday
night/Thursday as upper troughing develops to our west, resulting
deep southwest flow.  Surface low pressure develops in the Plains
and heads for the Great Lakes into Thursday.  After a mainly dry Wed
we should see snow developing in the warm advection wing Wed night,
but this mixes and then eventually change to mostly rain into
Thursday as the low is expected to track somewhere near Central Lake
Michigan by Thursday evening.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 701 AM EST Fri Dec 15 2017

Conditions are expected to dip into the MVFR category at all
locations this morning as lake effect snow showers sweep through
the TAF sites. KGRR and KMKG will be most affected, where
conditions will dip to IFR at times through about 16z.
Visibilities will improve this afternoon to VFR in most area
although MVFR ceilings will linger in many areas.

West-Southwest winds (240-260) will increase into the 12 to 25
knot range around 15-16z and remain at those levels until about

Tonight a band of snow will spread in from the south and
conditions should dip to MVFR again in all areas by Saturday at


Issued at 330 AM EST Fri Dec 15 2017

We expect building wave heights today due to increasing westerly
winds behind the passage of a trough of low pressure. The peak of
the wind should be around 18z to 19z and the waves should max out
this afternoon as well. Solid 7 footers look likely this afternoon
and early evening. Maintained the Small Craft Advisory as is which
is in effect through much of tonight. It will take some time tonight
before the wave field dampens out as the winds only slowly subside.
Winds are expected to remain below 20 knots through the weekend, so
a relative calm out of the lake for this time of year.


Issued at 330 PM EST Thu Dec 14 2017

Many rivers have iced over pretty quickly due to the snow and cold
temperatures. The Looking Glass near Eagle has risen above bankfull
due to downstream ice constricting the flow. It is expected to
gradually fall but some fluctuations are still possible. Mild
temperatures early next week may soften the ice a bit. Water frozen
in the snowpack ranges from 0.5 to 1 inch in most locations, but a
full snowmelt is not expected anytime soon.


MI...Winter Weather Advisory until 4 PM EST this afternoon for MIZ037-

LM...Small Craft Advisory until 5 AM EST Saturday for LMZ844>849.



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