Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 091834

Area Forecast Discussion
National Weather Service Grand Rapids MI
134 PM EST Mon Dec 9 2019


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


Issued at 1055 AM EST Mon Dec 9 2019

Low pressure is centered across Southern Wisconsin at 1030am with
a cold front extending to the southwest across Iowa. Southwest
Michigan is in the warm sector of the system at this point with a
steady rain just about to taper off. Much of the remainder of the
day will feature low clouds, drizzle and areas of fog.
Temperatures are near highs at this point with readings expected
to top out in the 40s in most areas and near 50 expected along
I-94. The cold front surges through the area overnight with
temperatures falling into the 20s. An abrupt change in the weather
tonight into Tuesday as compared to the last day or two.

We will be looking at potential headlines for late tonight
possibly through Wednesday as we go through the afternoon.
Headline decisions, if they are needed would be made with the
afternoon forecast package. The decision for headlines revolves
around travel impacts for the most part as snow amounts are
expected to be light. Snowfall on the order of an inch or two
across Western Lower Michigan with isolated spots to around three
inches are what we are expecting. A transition to much colder
weather, combined with some light snow may result in slower travel
and slippery conditions. We will hone in to find areas where the
snow may be heavy enough to create impacts. Again, significant
snow accumulations are not expected.

At this time we are planning to hold off on any Lakeshore Flood
headlines with this event as the high winds and waves look to be
of very short duration, 6 hours of less.


.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 MI.

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 18Z TAFS through 18Z Tuesday afternoon)
Issued at 135 PM EST Mon Dec 9 2019

Widespread IFR conditions are in place across the area at 100pm,
with LIFR nosing in from the west. The steadier rain is moving off
to the east leaving behind some drizzle and fog. The lower
ceilings will remain in the place into the evening hours, before
gradually lifting tonight.

A cold front will press in from the west this evening and sweep
across the TAF sites between 00z and 06z. A burst of rain and snow
will occur along the front as it passes through with ceilings
lifting in the wake of it.

Lake effect snow is expected overnight and into Tuesday as the
colder air flows over Lake Michigan.

A strong westerly wind is expected this evening with winds in the
15 to 30 knot range.


Issued at 1055 AM EST Mon Dec 9 2019

We have issued a Marine Dense Fog Advisory until 4pm for areas
north of Grand Haven in the area where the slack gradient from the
low will be.

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 are in effect.


LM...Dense Fog Advisory until 4 PM EST this afternoon for LMZ847>849.

     Small Craft Advisory from 7 PM this evening to 3 PM EST Tuesday
     for LMZ844>849.



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