Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211914
AFDGRR

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

LATEST UPDATE...
Hydro

.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 18Z TAFS through 18Z Monday afternoon)
Issued at 1257 PM EST Sun Jan 21 2018

Poor aviation conditions are expected the next 24 hours. IFR and
LIFR conditions are occuring along I-94 with ceilings below
1,000ft and visibilities in the 1 to 4 mile range. The low
ceilings will spread north this afternoon with visibilities
dipping considerably as we head into this evening. Widespread IFR
and LIFR conditons are expected tonight. Visibilities will dip to
around 1/4 mile tonight. Conditions will slightly improve on
Monday due to rain, but ceilings will remain low with visibilities
likely remaining under 2 miles.


&&

.HYDROLOGY...
Issued at 214 PM EST Sun Jan 21 2018

A complete melting of the natural snowpack is expected by Monday
in the Grand, Kalamazoo, and Muskegon river basins. This will
release a quarter to perhaps half inch of water. Rain totals on
Monday will mostly range between 0.6 and 1.2 inches (ECMWF and
ensemble have been 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 any ice jams that form can cause
unpredictable fluctuations in water levels. Road closures are
possible in low spots near river banks. Water could also approach
buildings in flood prone areas.

&&

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

$$

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



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