Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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678
FXUS63 KGRR 211700
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1200 PM EST Sun Jan 21 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 317 AM EST Sun Jan 21 2018

Low pressure will track through Lower Michigan on Monday and
Tuesday bringing rain on Monday which will change to snow by
Tuesday. Snow showers can be expected on Wednesday as colder air
returns.

&&

.UPDATE...
Issued at 1200 PM EST Sun Jan 21 2018

Scaled back a bit on the drizzle/rain today. It seems the moisture
will remain fairly shallow with minimal lift. A few isolated
patches of drizzle is all that is expected through 00Z.

Regarding ice potential over the northern CWA tonight. Temps have
already reached above freezing in this region and temps overnight
are only expected to dip slightly. With the main slug of rain not
coming until late tonight, feel temps will largely remain above
freezing. Headlines appear less likely, but we will continue to
evaluate.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 317 AM EST Sun Jan 21 2018

Forecast challenges are for extent of fog tonight and potential
for some freezing rain across the northern zones into early Monday.
There is also the timing of the changeover to snow Monday night
and Tuesday morning. There could even be thunder across the
southern zones Monday morning.

Looks like any freezing rain tonight will be confined to the far
north where temps and dew points will be at or below freezing
until about 15Z Monday. Precip during that time is not expected to
be heavy and no significant icing is forecast.

While that`s happening across the northern zones, we will have to
watch the thunder potential across the south, where there will be
elevated instability and strong lift as the warm conveyer belt
pushes into this area. The heavy rain threat will be mitigated by
the quick movement of the storm, with the dry slot moving in by
Monday afternoon.

Colder air wraps around Monday night and a the deformation zone
precip changes over to snow with some light accums possible on
Tuesday.

.LONG TERM...(Tuesday night through Saturday)
Issued at 317 AM EST Sun Jan 21 2018

An upper trough moving across the upper Midwest will provide low
chances for light snow Tuesday night through Wednesday night. Both
the ecmwf and gfs are in decent agreement with both the track and
timing of this system.

A nice shot of upper ridging will build in behind the departing
trough and temperatures will climb into the lower to mid 30s toward
the end of the week.

Rain chances will develop late Friday and Saturday as low pressure
strengthens in the Plains and then moves toward the Great Lakes. A
50 kt low level jet will bring abundant moisture northward toward
Michigan and we should see widespread rain as a result.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 641 AM EST Sun Jan 21 2018

IFR conditions will develop today and continue into tonight as low
clouds move in from the south. Areas of LIFR can be expected into
Monday morning. Winds will be southeast and east generally below
10 knots.


&&

.HYDROLOGY...
Issued at 225 PM EST Sat Jan 20 2018

A complete melting of the snowpack is expected Sunday/Monday in
the Grand, Kalamazoo, and lower Muskegon river basins. This will
release about a quarter to half inch of water. Rain totals on
Monday will probably range between 0.6 and 1.2 inches (ECMWF and
ensemble consistently lower than GFS and ensemble). Depth of
frozen soil varies but overall expect the ground to remain frozen
enough to allow efficient runoff.

A number of river forecast points will likely rise above bankfull
in the upcoming week. There is a chance of minor flood stage being
reached at a few sites (of earliest concern are Holt and Eagle),
particularly if higher rainfall totals verify. A breakup of river
ice is expected, and ice jams can cause local unpredictable
fluctuations in water levels. Road closures are possible in low
spots near river banks.

&&

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

$$

UPDATE...JK
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...04
AVIATION...Ostuno
HYDROLOGY...CAS



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