Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 052353
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
653 PM EST Tue Dec 5 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 355 PM EST Tue Dec 5 2017

Winter weather which includes lake enhanced snow showers,
temperatures remaining blow freezing is expected through the
weekend into next week. Areas well east of US-131 should expect
mostly cloudy skies and occasional snow flurries through most of
this time into Friday but clipper systems will move through the
area over the weekend and also into early next week brings a more
widespread snow. Temperatures will mostly remain blew freezing
through the middle of next week.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 355 PM EST Tue Dec 5 2017

The main issue is our issuing a Winter Weather Advisory for late
Wednesday afternoon into Thursday afternoon for Lake Shore areas.

The wind advisory did nicely today. Even so I will allowed it to
expire at 7 pm since by then winds will have decoupled and that
will diminish the wind gusts.

There is a shortwave rotating around the upper low centered over
Hudson Bay this afternoon (moving into Northern Minnesota at 3
pm). This shortwave will bring shortwave ridging to the area this
evening making the moisture depth to shallow for lake enhanced
snowfall. Skies may even partly clear for a time tonight since the
air gets that dry this evening.

On Wednesday the shortwave moves through our area bringing the
core of the deep cold air over southern Michigan for tomorrow
afternoon into Thursday. This puts the northern edge of the polar
jet south of Michigan. With 850 temps near -14c, and deep
moisture (1000 to 500 rh increase to 80% Wednesday evening) will
allow the DGZ to saturate and that will result in lake enhanced
snowfall. Seems there will be a dominant snow band setting up
after midnight (early Thursday) from near Holland to Kalamazoo.
This should remain in place till mid morning Thursday. Most of the
snowfall I have in the grids comes from that snow band. Since
this is expected to be the first widespread measurable snow over
the western CWA and since I expect as much as 6 inches to fall in
parts of Southwest Allegan County by late morning Thursday I
issued a Winter Weather Advisory for late Wednesday afternoon into
Thursday afternoon to cover this snowfall event.

The snow should come to an end by Thursday evening. Shortwave
ridging will once again end the significant snowfall event by
early Thursday evening.

.LONG TERM...(Friday through Tuesday)
Issued at 355 PM EST Tue Dec 5 2017

Periodic lake effect snow is expected through the long term. We will
remain cold enough for lake effect the entire long term, with benign
lake effect snow enhanced by shortwaves moving through the northwest
flow.

The upper shortwaves will act to give the lighter lake effect snow a
boost via synoptic scale lift and added moisture. The main
shortwaves at this time appear to be moving through our area Friday
into Saturday and again Monday into Tuesday. There may be a bit of a
lull in the activity from Sunday into Monday.

The heavier snow through the long term looks to be Friday night into
Saturday and Monday night into Tuesday. These time frames look to be
when the deepest moisture and best cold air advection correspond.

We will not see accumulating snow the entire long term but in the
periods where the shortwaves are moving through, we will see snow
add up. Temperatures will remain slightly below normal for highs
from around 30 to the lower 30s for the most part.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 653 PM EST Tue Dec 5 2017

VFR conditions expected through early Wednesday. Winds will
continue to gust near 30 knots tonight then diminish on Wednesday
but there will still be gusts over 20 knots through the morning.
Some snow showers could bring areas of MVFR by afternoon near Lake
Michigan.

&&

.MARINE...
Issued at 355 PM EST Tue Dec 5 2017

I will allow the gale warning to continue overnight. The core of
the strongest winds move through the area early tonight however
the winds only slightly decrease in the boundary layer after
midnight. By mid morning however winds will decease into the 30
knot range. So our current expiration time seems fine.


&&

.HYDROLOGY...
Issued at 345 PM EST Thu Dec 5 2017

Precipitation will fall as rain through tonight before colder air
rushes in behind a strong cold front and precipitation transitions
to snow. Total rainfall from this morning through Tuesday morning is
expected to range between 0.25 and 0.70 inches, which will not be
enough to cause significant rises on rivers and streams. Totals
exceeding 0.5 inches will most likely occur along and north of I-96.
A few thunderstorms may develop late this evening and overnight.
These would produce locally heavier rainfall amounts, and could
result in water ponding on roadways and low-lying areas.

Precipitation from Tuesday afternoon into the weekend will fall as
snow as temperatures remain below freezing. High snow-to-liquid
ratios will result in some snow accumulations (especially near the
lakeshore), but no significant liquid-equivalent accumulations.

&&

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

     Wind Advisory until 7 PM EST this evening for MIZ037>040-043>046-
     050>052-056>059-064>067-071>074.

LM...Gale Warning until 4 AM EST Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...Duke
AVIATION...Ostuno
HYDROLOGY...HLO
MARINE...WDM



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