Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 201150
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
650 AM EST Sat Jan 20 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 258 AM EST Sat Jan 20 2018

Low pressure will move through Lower Michigan by early next week,
bringing mostly rain Sunday and Monday, then ending as snow
Tuesday and Wednesday.

&&

.SHORT TERM...(Today through Monday Night)
Issued at 258 AM EST Sat Jan 20 2018

Precip type is the main focus of the short term as moisture
streams up from the south tonight with light rain and some
potential for freezing rain at the onset. Temps and dew points
are near freezing after midnight but warm advection at the
surface should mean a change over to rain before much in the way
of icing occurs.

The main batch of the precip lifts through on Monday and should be
all rain, then the sfc low tracks across the northern zones Monday
night with a gradual transition to snow Tuesday morning as the
upper low brings thickness cooling. Some light accums are
possible by late Monday night.

.LONG TERM...(Tuesday through Friday)
Issued at 258 AM EST Sat Jan 20 2018

Low pressure will be moving from northern Lower Michigan to Ontario
Tuesday. Cold air will begin flowing back across the cwa and any
lingering rain will mix with and change to light snow as the low
moves away. Some surface troughiness coupled with the upper trough
moving through will result in some light snow Tuesday. A brief
period of lake effect snow is possible Tuesday night along the lake
shore, but moisture will be a limiting factor as drier air moves in
from the west.

Another short wave moves across the cwa Wednesday, but high pressure
at the sfc will limit pcpn. A ridge building over the Midwest will
boost sfc temps into the 40s toward the end of the week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 650 AM EST Sat Jan 20 2018

VFR conditions will continue into this afternoon then low clouds
will move in this evening with ceilings around 1500 feet. IFR
conditions are expected after midnight as low clouds and fog
increases. Southwest to south winds around 10 to 12 knots today
and less than 10 knots tonight.

&&

.HYDROLOGY...
Issued at 328 PM EST Fri Jan 19 2018

The latest update from the Muskegon River ice jam in Mecosta County
is that slow improvement continues. Chunks of ice remain in the
river, but are stable at this point with slowly falling river
levels. Minor flooding is ongoing immediately along the river bank
in low lying areas.

A limited snowmelt will occur Friday and Saturday as high
temperatures climb to around 40, then a more rapid melting of the
snow cover is likely Sunday and Monday as dewpoints climb above 32
degrees and winds increase. The snowmelt will be more complete in
southern Michigan where warmer air and higher dewpoints will be in
place for longer. Water contained within the snow is in the ballpark
of a quarter inch. Rainfall on Monday will likely range from a half
to one inch. Much of this water will efficiently run off into rivers
and streams due to frozen soil.

The combination of ice jams and runoff will increase the risk of
river flooding next week. Nuisance flooding in the typical flood-
prone spots is a good bet. Flooding encroaching on vulnerable homes
and businesses is less certain but will have to be monitored.

&&

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

$$

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



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