Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211800
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
100 PM EST Tue Nov 21 2017

LATEST UPDATE...
Aviation/Hydro

.SYNOPSIS...
Issued at 330 AM EST Tue Nov 21 2017

A cold front is located across the Western Great Lakes this morning
stretching from the U.P. of Michigan into Wisconsin. The front will
push through Southwest Lower Michigan through the course of the day.
Some rain showers will accompany the frontal passage, especially
across Southern Lower Michigan. Cold air will pour into the area
behind the front and touch off some snow showers as early as this
afternoon. Light lake effect snow showers will continue tonight
towards Lake Michigan with little to no accumulation. A weakening
clipper system may bring a little bit of light snow late Wednesday
night into Thanksgiving morning. Temperatures will tumble out of the
40s and into the 30s this afternoon after the front moves through.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EST Tue Nov 21 2017

Overall minor precipitation events are expected during the short
term with no major systems. The precipitation events include light
rain ahead of today`s front, which may change to a bit of light snow
this afternoon before tapering off. A lake effect snow period from
this evening into Wednesday morning and the chance for some light
snow Thanksgiving morning.

As for today`s front, models have been consistent in showing light
rain breaking out over Southwest Lower midday and expanding some
this afternoon over the southern half of the forecast area or along
and south of I-96. Some of the precipitation may mix with and change
over to some light snow as the cold air advection is healthy. The
NAMnest has temps in the upper 20s to mid 30s in all areas by 22z.
This may be a tad cold but not far off.

Tonight, moisture depth is limited, but BUFKIT overviews do show
moisture reaching near the 7,000ft mark which is not bad. Expecting
wind parallel snow bands in northwest flow. Given the moisture depth
issues most of the time, flake size will likely be small and
accumulations should be limited to less than an inch at best. The
exception may be down towards Van Buren county where a long fetch
may allow the LES to overperform just a bit. We will be keeping an
eye on radar trends tonight down towards South Haven.

A sneaky event appears possible late Wednesday night into
Thanksgiving morning with a weakening clipper system. Moisture
increases ahead of the clipper and delta t`s will still be cold
enough for lake effect processes to kick off. Would not be surprised
to see some southwest flow lake enhancement occur Thanksgiving
morning in the northwest CWA towards Ludington, Newaygo and Baldwin.
Have added pops to the forecast at this point and we will need to
monitor forecast trends. Any accumulations of snow would be light,
but the NAM is kicking out near a tenth of liquid equiv.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EST Tue Nov 21 2017

The focus of the long term is a clipper that moves across Ontario
Friday and Saturday. The ecmwf and gfs are similar in strength of
the low but the gfs is farther north.

We`ll see increasing cloudiness Friday as the clipper moves toward
the upper Great Lakes. Light rain associated with isentropic lift in
the warm sector looks like it will be north of the cwa. So we`re
left with precipitation along the cold front late Friday afternoon
which is supported by low condensation pressure deficits. The better
chance of precipitation will arrive Friday night when the trailing
short wave moves over the cwa. We have likely pops over most of the
cwa as rain. Lingering precipitation behind the wave will mix with
and change to light snow as colder air wraps in behind the system. A
few snow showers may be possible near the lake shore Saturday night
as h8 temps near -12c briefly move across. Moisture depth is shallow
though and accumulations aren`t expected.

Friday will be the warmest day as southwest winds push temperatures
into the mid to upper 40s. Then temperatures fall into the 30s for
Sunday and Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 100 PM EST Tue Nov 21 2017

Band of rain will produce areas of MVFR cigs/vsbys this
afternoon, mainly south and east of GRR. Moderate icing in the
clouds is likely within this southeastward moving band of rain,
with current freezing levels around 2000 ft falling through the
afternoon.

The rain will be out of the area by 00Z with VFR following in
it`s wake tonight and Wednesday. However there will be lake effect
snow showers this evening that could occasionally/briefly impact
MKG and AZO with MVFR or lower conditions. West winds gusting to
25 kts will becoming northwest and subside to around 10 knots this
evening.

&&

.MARINE...
Issued at 330 AM EST Tue Nov 21 2017

Gales are still occurring at the marine observation sites along the
lakeshore early this morning, so will continue the Gale Warning into
the mid morning hours. A Small Craft Advisory is going to be needed
on the back end of this Gale to allow the waves to settle down which
is going to take some time. The SCA will likely be needed through
both the remainder of today and tonight and even into Wednesday
morning. Wave models are indicating waves subsiding to below 4 feet
during the late morning hours of Wednesday. It looks like we are
going to need another SCA early Thanksgiving morning into
Thanksgiving day. It is certainly fall on the Great Lakes with
plenty of rough weather.


&&

.HYDROLOGY...
Issued at 100 PM EST Tue Nov 21 2017

Several rivers remain at advisory/action stage level as runoff
continues from rain that fell over the weekend. Water levels in
these and other rivers will remain fairly steady or slowly fall
through the end of the week. Rain and snow showers today and tonight
will only provide light amounts of precipitation, and will not have
an impact on water levels in rivers, creeks and streams. Additional
flooding is not expected.

A few more rounds of light rain/snow are expected through the end of
the week, but should not have a significant impacts on river levels.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 AM EST Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...Meade
HYDROLOGY...HLO
MARINE...Duke



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