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fxus63 kgrr 121145 
afdgrr

Area forecast discussion
National Weather Service Grand Rapids Michigan
645 am EST Thu Dec 12 2019

Latest update...
aviation

Synopsis...
issued at 258 am EST Thu Dec 12 2019

- warm advection light precipitation this afternoon (light snow /
to drizzle)over northern County Warning Area

- light freezing drizzle west and north overnight/ some travel
impacts possible by Friday morning

- cold front brings lake effect snow Saturday night into Sunday
morning. Expect some light accumulations west of US-131

- significant snow event possible (looking more likely) Monday
afternoon into Tuesday. Colder with lake effect into Wednesday.

&&

Discussion...(today through next wednesday)
issued at 258 am EST Thu Dec 12 2019

There are three major systems heading our way in the next week.
First is a weak system that should bring US mostly light snow to
drizzle northwest today and freezing drizzle tonight. Then a major
East Coast storm will pull cold air into this area late Saturday
into midday Sunday, that will bring a 1 to 3 Inch Lake effect
snow event with it. Finally there is still the potential for a
major snow storm later Monday into Tuesday morning.

Afternoon and overnight system...

We have a weak shortwave tracking through the Great Lakes today
but the problem is there is a much stronger system upstream, on
the southern branch of the polar jet, coming on shore as I write
this. That will cause our system today to minor out as it moves
through the area. Which means the front stalls near US tonight as
the next upstream system pushes warm air back toward US due to the
digging trough, which by sunrise Friday will be over the Midwest.
The warm advection lift precipitation will mostly be north of our
County Warning Area today into early tonight. However as the front stalls we have
a persistent southwest winds (50 to 60 knots between 900 and 800
mb) which brings warm air into our area. Our surface temperatures
will rise above freezing south of Route 10 by midday. The freezing
level rises to near 2000 ft by evening. So any light snow with the
warm advection push (near Route 10 this afternoon) will change to
light rain or drizzle by late in the day.

Tonight the deep moisture moves out so the dgz will not be
saturated but the speed convergence and stalled front will trap
low level moisture and cause some drizzle tonight, mostly from the
Lake Shore to US-131. The question is will the surface temp fall
below freezing? Inland north of GRR has the best chance but that
area may be to far inland to see much drizzle. So for now no
weather advisory but we may need one if the next shift believes
there is a greater risk of accumulating freezing drizzle.

Saturday Evening Lake snow event....

This is the big East Coast storm that will bring the cold air back
into our area. However the cold air push will be shortlived as an
even strong system comes onshore over the western Continental U.S. Saturday.
That will force the shortwave trough brining the cold air in east.
Even so we get about 18 hours of cold enough air and deep enough
moisture for lake effect snow. This seems like a 1 to 3 inch sort
of event.

The Monday system...

The GFS has been forecasting this for nearly a week now and the
European model (ecmwf) has since the 10th /00z run been bringing the storm closer
to US on the operational runs. The 12/00z run brings snow to GRR
from the European model (ecmwf). Since this is polar closed upper low dropping
south into and southern stream system, this could be power house
storm. We will have to watch this closely.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 632 am EST Thu Dec 12 2019

A weak area of low pressure will track towards the western Great
Lakes today. The most likely impact at taf sites will be
southerly winds gusting between 20 and 30 knots, potentially
higher at mkg. Low-level jet will bring a core of higher winds
aloft, with 40-50 knots at 2000 feet causing low-level wind shear
from late morning into tonight. Precipitation will be limited at
taf sites with this system and mostly affect central and northern
Michigan. Temperatures look warm when precipitation arrives into
mkg, and will carry only a rain mention. As we cool overnight,
there is some potential for light snow or freezing drizzle there,
but by then much of the precipitation will have ended. Watching
potential for drizzle or freezing drizzle overnight not just at
mkg, but also GRR.

&&

Marine...
issued at 258 am EST Thu Dec 12 2019

Winds will start out strong from the southeast this morning, then
increase further from the south by this afternoon, allowing wave
heights to build into the 7 to 11 foot range, mainly north of
Holland. There is potential to see a few gale force wind gusts as
well, mainly from Holland northward and between 1pm and 9pm.
Onshore flow will also bring a risk for minor flooding and beach
and dune erosion for areas vulnerable to southerly flow. Wind
speeds will decrease overnight as low pressure passes to our
north, with wave heights subsiding Friday morning.



&&

GRR watches/warnings/advisories...
Michigan...Lakeshore flood advisory until 7 am EST Friday for miz037-043-
050-056.

Lm...Small Craft Advisory until 7 am EST Friday for lmz844>849.

&&

$$

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