Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 061610
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1110 AM EST Wed Dec 6 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 316 AM EST Wed Dec 6 2017

An arctic airmass will continue to flow in from Canada over the
next couple of days. This will lead to widespread lake effect snow
showers with accumulations expected downwind of the lakes. This
will result in slick travel conditions at times.  Below normal
temperatures are forecasted through the end of the week.

&&

.UPDATE...
Issued at 1110 AM EST Wed Dec 6 2017

Inversion heights will continue to rise through the rest of the
day. We were already seeing back building clouds over Lake
Michigan north of Grand Haven as of 16Z. The added moisture will
result in increasing lake effect snows. Much of it will get
started by about 18Z, with an increase in intensity by 22Z. Accums
through 00Z will be an inch or less mainly along and west of U.S.
131.

&&

.SHORT TERM...(Today through Friday)
Issued at 316 AM EST Wed Dec 6 2017

One area of flurries was tracking eastward through portions of
Illinois and Iowa. The latest high res models suggest that this
feature may lead to a small band of snow showers through Van
Buren and Kalamazoo counties and perhaps further east. I did bump
up morning POPs for southern locations to account for this
feature. Then this afternoon and into the evening...the moisture
deepens up from NW to SE for much of the CWA. It looks like the
DGZ becomes saturated. Thus impacts should become more likely.

A noticeable surface trough tracks through the CWA during the day
on Thursday. This feature will likely support some heavier snow
showers. During the morning commute Thursday...snow showers
should be widespread...with perhaps a band extending well inland
through Kalamazoo and perhaps further east. May need to expand the
headline further east if this is the case. No changes needed to
the headline at this time.

.LONG TERM...(Friday night through Tuesday)
Issued at 316 AM EST Wed Dec 6 2017

Cold weather is going to be here for a while and we`ll have several
opportunities for light snow through the period. A deep upper long
wave trough over the Great Lakes will result in periodic
reinforcements of cold air, which will in turn boost the lake
effect.

Friday and Monday are the best chances at seeing snow. A strong
short wave rotating through the upper flow is progd to induce low
pressure at the sfc over Michigan late Friday night. The boost in
moisture and lift will result in snow, but mainly over the western
cwa. The colder air...h8 -10c to -16c...doesn`t move in until
Saturday morning. Boundary layer wind progs are in the 340-360
degree range which points to lake effect snow mainly near the lake
shore. Inland areas may see some light snow from the sfc low, but
the lake effect will remain over the western cwa.

Warmer air moves across the southern half of the cwa Monday ahead of
the next cold front and that may result in some mixed rain and snow
until the arctic air moves back in Monday night.

A strong shot of arctic air moves in Tuesday and h8 temps fall to
near -16c by late in the day. But once again, wind profiles point
toward the lake shore for the best chance at seeing lake effect
snow.

Overall, kind of a snowy pattern near the lake shore, but not much
accumulation expected inland. Highs through the period will be a few
degrees either side of 30.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 521 AM EST Wed Dec 6 2017

Snow showers will be on the increase today leading to some impacts
by tonight. MVFR conditions will become more widespread as the
arctic airmass continues to flow in leading to lake effect snow
showers. Local sub IFR may occur in any heavier snow
bands...mostly after 21z. Gusty winds with some over 25 knots
remain possible through much of the afternoon.


&&

.MARINE...
Issued at 316 AM EST Wed Dec 6 2017

I extended the gale warning til 10 am. The winds are slowly coming
down...but gales are still occuring. Hazardous boating conditions
for small craft will likely exist through much of the period.


&&

.HYDROLOGY...
Issued at 534 AM EST Wed Dec 6 2017

Lake effects and the passage of several weak storm systems will
generate periodic snowfall through the middle of next week.
Temperatures will remain cold enough for precipitation to fall as
almost all snow. The total liquid equivalent from snowfall through
Friday is expected to remain below a quarter of a inch. This is not
expected to cause any issues with rivers and streams, or flooding.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 4 PM this afternoon to 4 PM EST
     Thursday for MIZ037-038-043-050-056-064-071-072.

LM...Small Craft Advisory until 7 AM EST Friday for LMZ844>849.

&&

$$

UPDATE...JK
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...MJS
HYDROLOGY...HLO
MARINE...MJS



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