Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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172
FXUS63 KGRR 131155
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
655 AM EST Wed Dec 13 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Wed Dec 13 2017

A fast moving clipper system will pivot through the Southern Great
Lakes today moving from Southeast Minnesota this morning to portions
of Northern Ohio this evening. A swath of accumulating snow is
expected across the southwest quarter of Lower Michigan today and
this evening. The lowest accumulations will be in the far southwest
towards South Haven and Kalamazoo where 2 to 4 inches may fall by
midnight. Further north a swath of 5 to 8 inches is expected along
and north of Interstate 96. The heaviest snow will likely fall along
a line from Pentwater southeast towards Alma and St. Johns. A period
of quieter weather is expected from late tonight through Thursday.
Another period of snow is expected from late Thursday night into
Friday with an enhancement off the lake.

&&

.SHORT TERM...(Today through Friday)
Issued at 330 AM EST Wed Dec 13 2017

Made changes to the going headlines based on latest model guidance
and coordination with APX, DTX and IWX. Latest model trends show the
swath of heavier snow to be in a corridor along and potentially
north of Interstate 96. Therefore, dropped the warning that was in
place from Ottawa south down the lakeshore. The feeling is the
heaviest swath will likely be on a line from Oceana County towards
Gratiot and Clinton Counties. Expecting a quick hitting 5 to 8
inches today, where snow rates may reach an inch an hour this
afternoon. The evening commute will be the most impacted by falling
snow, slippery travel and limited visibilities.

The models show the 850mb low traversing far Southwest Lower
Michigan where the precipitation will be hit and miss at times down
towards South Haven. Strong isentropic lift is noted on the north
side of the low in the warning area. A well defined cross hairs
signature can be seen as well in some of the BUFKIT overviews with
significant lift in the DGZ. The snow will wind down this evening
and come to an end by midnight.

A lull in the activity is expected from late tonight through
Thursday. The lull will be short lived though as another lake
enhanced event is taking shape for late Thursday night and Friday.
Several inches of accumulation will be possible across Western Lower
Michigan.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM EST Wed Dec 13 2017

A pattern shift still appears in order by the weekend and lasting
into the middle of next week.  Temps won`t be as cold, and pcpn
won`t be as frequent or steady.

Friday night will continue to see lake effect snows as inversion
heights remain high with a WNW flow.  However H8 temps climb into
Saturday and the lake effect will dwindle.  The warming aloft will
result as a warm front forms near the MI/IN border, and the upper
flow becomes more zonal.

A cold front and mid level short wave will move in by Sunday
afternoon and evening.  This will bring a period of snow across the
CWA, possibly mixed with rain along and south of I-96.  But overall
the pcpn appears light.  Behind the front Monday and Tuesday only
appears slightly cooler, but still not cold enough for lake effect.
The models show additional weak short waves coming through
Monday/Tuesday with varying timing.  This is enough to keep low POPs
in.  Tuesday`s wave appears a bit stronger so will have slightly
higher POPs then.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 655 AM EST Wed Dec 13 2017

Aviation conditions are expected to deteriorate this morning as an
initial band of snow moves into the area from the west. More
widespread snow and a further deterioration is expected this
afternoon and evening. Conditions will reach the MVFR category in
all areas this morning and drop into the IFR category this
afternoon. This afternoon and evening ceilings will likely be
below 2000ft with visibilities that will vary between 1/2 mile
potentially and 2 miles. A rapid improvement is expected tonight
as the low responsible for the adverse weather moves away. VFR
conditions should develop overnight.

&&

.MARINE...
Issued at 330 AM EST Wed Dec 13 2017

Winds and waves will pose a hazard to small craft into this evening.
Low pressure will move southeast across southern Lake Michigan
today. The result will be stronger south winds this morning, turning
north tonight. The wave field will likely fill into our nearshore
marine zones, but the highest waves will be over the open waters. A
weaker wind field will be in place on Thursday.


&&

.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 Weather Advisory until 11 PM EST this evening for MIZ039-
     040-056-064-065-071>074.

     Winter Storm Warning until 11 PM EST this evening for MIZ037-038-
     043>046-050>052-057>059-066-067.

LM...Small Craft Advisory until 10 PM EST this evening for LMZ844>849.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...JK
AVIATION...Duke
HYDROLOGY...63
MARINE...Duke



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