Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 201925

Area Forecast Discussion
National Weather Service Grand Rapids MI
225 PM EST Sat Jan 20 2018


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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1216 PM EST Sat Jan 20 2018

Solid VFR prevails at 17z across the GRR TAF sites. This is
expected to continue through sunset. However there is a area of
low stratus heading northeast from MO and IA as I write this. That
area of low clouds will reach the I-94 TAF sites by 03z and the
I-96 TAF sites by 06z (or so). This will bring IFR to LIFR cigs to
all TAF sites in our CWA by 06z.

Seems fog would be a issue tonight too as significantly higher
surface dew point air heads this way as while surface winds become
light, that makes a good case for dense fog. Both the NAMNest and
the RAP model visibility forecast show less than 1/4 mile
visibilities between I-94 and I-96 between 06z and 12z. As a
result in brought dense fog into all of the I-94 TAF sites and
also GRR. By mid morning there should be enough moisture and lift
so as to lead to drizzle, that will increase visibilities to
around a mile, possibly 2 miles. Thus IFR conditions will
continue through Sunday into Sunday night.


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.




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