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fxus63 kgrr 090821 

Area forecast discussion
National Weather Service Grand Rapids Michigan
321 am EST Mon Dec 9 2019

Latest update...

issued at 321 am EST Mon Dec 9 2019

-mild with rain, drizzle, areas of fog today

-drizzle changing to areas of light snow late tonight

-much colder Tuesday and wednesday; lake effect snow showers but
only minor accumulations


Discussion...(today through next sunday)
issued at 321 am EST Mon Dec 9 2019

The primary fcst challenge is the extent of any travel impacts
related to the incoming cold snap. The lake effect potential with
this system has been looking less impressive with each model run
and snow amounts for most areas may very well be under one inch.

The problem is the dry air and subsidence associated with the
large 1040 mb sfc high which builds in from the west. Inversion
heights are only around 4k ft in the cold air on Tuesday and
Wednesday which should really hold down amounts. So despite Delta
t's of 20c or more, this does not look like a Big Lake effect
event for SW lwr Michigan.

The other question is whether or not we develop slick spots on the
roads by the Tuesday morning commute from freezing of residual
moisture on the roads - even in the absence of accumulating snow.
This is not a sure thing either since the bulk of the rain with
this system falls this morning and generally only light amounts of
mainly drizzle occur this afternoon and tonight.

As such it's questionable if there will even be much standing
water/moisture on the Road to freeze when sfc temps fall below
freezing late tonight. Also with temps approaching 50 today, the
ground and roads may hold some warmth for a time beyond the big
temperature plunge late tonight.

The mid week cold air does not stick around very long and
guidance has highs above freezing returning by Friday and
continuing into next weekend. No big systems are foreseen in the
next 7 days although there are hints of a potentially impactful
system a week from Tuesday.

Also of note, in the near term, sfc dew points at or above 40
moving over the snowpack north of I-96 will result in areas of fog
today which could be locally dense.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1234 am EST Mon Dec 9 2019

The moisture continues to stream in from the Gulf of Mexico which
is leading to the lowering of the cloud bases and visibility
across the region. Kmkg has dropped down to IFR and that should be
the trend for the remainder of the sites in southwest lower Michigan
through the night. Rain will be developing as well. The
rain/drizzle will persist through Monday. Colder air will start
working its way in Monday evening from the northwest. That will
transition the precipitation to snow which could persist for a
couple of hours. Gusty west winds will develop Monday
evening...ushering in the cold airmass.


issued at 321 am EST Mon Dec 9 2019

Winds and waves will increase substantially tonight as the Arctic
air pours in on northwest winds. Winds could flirt with gales for
a time. Small craft advisories will be issued, and we could
also need another Lakeshore flood advisory south of Muskegon.
Will take a closer look at that today.


GRR watches/warnings/advisories...
Lm...Small Craft Advisory from 7 PM EST this evening through 3 PM
Tuesday for lmz844>849.



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