Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 122328
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
628 PM EST Tue Dec 12 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 322 PM EST Tue Dec 12 2017

Lake effect snow continue along the lake shore with scattered snow
showers inland. A clipper will move across the state Wednesday
bringing accumulating snow to much of southwest Lower Michigan. Yet
another clipper will move across the state Friday bringing more snow
to the region.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 322 PM EST Tue Dec 12 2017

Forecast concerns deal with ongoing lake effect snow and the next
clipper arriving tomorrow morning.

Lake effect continues along the lake shore where visibilities have
briefly fallen to less than a mile throughout the day. Conditions
remain very favorable for lake effect snow to continue tonight.
Cross sections show that lift is centered in the DGZ through much of
the evening. Expect several inches more snow in the warning area.

We discontinued the advisory for Lake and Newaygo counties and the
warning for Kalamazoo county, but kept the warnings going overnight
along the lake shore.

The next system is a clipper that will move from Minnesota across
northern Illinois. HiRes models indicate snow will develop around
12z along the lake shore and spread inland. For that reason, we
extended the winter storm warning until Wednesday evening and issued
a winter weather advisory for the non lake shore counties...also
until Wednesday evening.

Pretty good pressure advection was noted with this system and a
deformation axis will likely set up near a MKG-LAN line. We`re
looking at 5 to 7 inches of snow with this system within 40 miles of
this line with lesser amounts in the northeast and far southwest
cwa.

Colder air will be brought south behind the departing clipper and
more lake effect snow can be expected Thursday and Thursday night.

.LONG TERM...(Friday through Tuesday)
Issued at 322 PM EST Tue Dec 12 2017

Fast flow regime continues through the extended with the usual model
differences in timing and amplitude of embedded shortwave features.
Fairly high confidence for Friday with a clipper and quick shot of
arctic air bringing some snow into Saturday morning.

Warm advection pattern is already underway by Saturday evening as
Plains low makes a run at Lower Michigan on Sunday into Monday.
Forecast confidence decreases here as low track is uncertain and
whether Gulf moisture transport reaches here, along with precip type
if it does. Did not deviate from blended POPs here...although they
are not representative of 12Z operational ECMWF, which would be
higher across the southern half of the forecast area.

Once that low gets past it looks like temperatures drop again with
some lake effect snow in west flow on Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 625 PM EST Tue Dec 12 2017

The lake effect snow showers were gradually diminishing in
intensity. They will continue to linger for part of the
evening...leading to some impacts...mainly for KAZO and KMKG.

The next low pressure system seems to be moving in quicker looking
at radar. This will be a widespread impactful snow event for the
TAF sites on Wed. One thing to watch is if the axis of heavy snow
lifts north of KAZO...KBTL and KJXN during the day. If so there
could be a several hour window of VFR conditions roughly after
17z for these sites.

&&

.MARINE...
Issued at 322 PM EST Tue Dec 12 2017

Wind continues to slowly subside and most locations are under gale
force. Therefore, we discontinued the gale warning and issued a
small craft advisory through Wednesday afternoon. Waves will
continue to be well above 3 feet through tonight.


&&

.HYDROLOGY...
Issued at 1028 AM EST Tue Dec 12 2017

Rivers are running near normal levels. No flooding or significant
rises in river levels are expected. Snow is forecast periodically
through the week.

Temperatures have been around to below freezing for a week and
similar temperatures are expected to persist through the end of this
week. This should allow some ice to begin forming on area rivers,
especially on the Muskegon River in Central Lower Michigan.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning until 11 PM EST Wednesday for MIZ037-043-
     050-056-064-071.

     Winter Weather Advisory from 7 AM to 11 PM EST Wednesday for
     MIZ038>040-044>046-051-052-057>059-065>067-072>074.

LM...Small Craft Advisory until 4 PM EST Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...Ostuno
AVIATION...MJS
HYDROLOGY...63
MARINE...04



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