Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191148
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
648 AM EST Sun Nov 19 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Sun Nov 19 2017

Strong low pressure will move away from the Great Lakes today into
eastern Canada. Cold winds blowing over Lake Michigan will continue
to produce snow showers through much of the day before ending late
this afternoon and evening. Little to no snow accumulation is
expected, but a dusting is certainly possible. Normal highs for this
time of year are in the middle 40s and many areas will remain below
the freezing mark all day. Dry weather is expected tonight and
Monday as southerly winds increase ahead of a clipper system passing
well off to our north. The clipper will push a cold front through
our area on Tuesday bringing small chances for precipitation. After
highs back in the 40s for Monday and Tuesday we cool back into the
30s behind the front for Wednesday.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 330 AM EST Sun Nov 19 2017

No significant weather concerns really in the short term. Focus is
on lake effect snow showers today and small chances for
precipitation on Tuesday.

The mid lake buoy is reporting a water temp of +9C this morning so
-4C air at 850mb is cold enough to produce lake effect snow if
enough moisture is present. The thermal trough swings through this
morning with -12C air at 850mb`s so we are looking at fairly robust
instability this morning with delta T`s around 20C. Moisture is not
all the deep, on the order of 5,000ft to 7,000ft. More than enough
for LES though. Conditions should begin to become unfavorable this
afternoon as the moisture depth decreases to below 4,000ft and the
DGZ becomes unsaturated. Winds shift a bit more westerly as well
which will take upstream preconditioning out of play off of Lake
Superior. Bottom line, snow showers will continue with occasional
bursts of moderate snow through midday. The snow showers should
begin to fade early this afternoon and move inland and diminish
later this afternoon. Any accumulations will be on the order of a
dusting to potentially around a half inch in spots.

Tonight through Monday night look dry and increasing breezy as a
decent gradient builds in ahead of the clipper system passing off to
our north. Tuesday a front will push through the forecast area. We
will see a few showers along and ahead of the front mainly towards
Lansing and Jackson in the afternoon. In addition behind the front a
few snow showers will be possible late in the day across Central
Lower. Moisture is pretty limited though with the frontal passage.
The afternoon snow showers up north will be of the lake effect
variety as the cold air advection behind the front is strong.

.LONG TERM...(Tuesday night through Saturday)
Issued at 330 AM EST Sun Nov 19 2017

A deep upper trough will quickly move across the state Tuesday night
into Wednesday. H8 temps briefly fall to around -12c behind the
trough. There isn`t a lot of moisture with this system and we don`t
expect much in the way of lake effect, but we added a low chance pop
to the model solutions that didn`t have any.

We expect dry weather Wednesday and Thanksgiving Day, so travel
conditions across southwest Lower Michigan should be good during
that time. Toward the end of the week, however, a stronger cold
front may bring mixed precipitation to the region.

The cold front is progd to move across the lake Friday night. But,
similar to the current situation, boundary layer moisture is on the
low side. H8 temps fall to around -12c, so there should be enough
instability over the lake to create some snow showers, but the lake
of deep moisture will preclude any appreciable accumulations.

Highs will be mostly in the 30s through the period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 647 AM EST Sun Nov 19 2017

Lake effect stratocumulus clouds will continue to stream off of
Lake Michigan today with variable ceilings between 1500ft and
4000ft. So, expect conditions to vary between MVFR to VFR through
the course of the day. An improving trend will be noted though
this afternoon and evening from west to east. The ceilings should
lift to VFR for good between 20z and 00z. Snow showers will
continue into mid afternoon with a gradual diminishing trend as
well. Some MVFR visibilities are possible in the heavier snow
showers through early afternoon.

Winds will be from the west-northwest today at 10-20 knots with
gusts to around 24 knots at times.

&&

.MARINE...
Issued at 330 AM EST Sun Nov 19 2017

Winds have fallen below gale force this morning and we have
downgraded the Gale Warning to a Small Craft Advisory. The SCA runs
through 18z on Monday at this point, given we could be looking at
southwest gales Monday afternoon and Monday night. Typical rough
conditions out on the big lake right through Tuesday night with
waves larger than 4 feet that entire time. Waves will be large this
morning with 8 footers still being reported at the southern Lake
Michigan buoy. We could be looking at 10+ footers again Monday night.


&&

.HYDROLOGY...
Issued at 1200 PM EST Sat Nov 18 2017

Observed rainfall amounts are on pace to be in fairly good
agreement with forecasts. As a result, several rivers are
expected to rise over the weekend. Most sites will remain within
banks, while those exceeding banks are within the Grand and
Kalamazoo basins. This is where most of the rain has fallen and is
also where the second wave of precipitation is expected to be
greatest. The only site projected to get close to flood stage is
Holt on the Sycamore Creek.

The positive news is that while minor flooding can be expected
immediately along streams and rivers, any larger impacts should be
mitigated by quieter conditions in the upcoming week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 1 PM EST Monday for LMZ844>849.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...Duke
HYDROLOGY...JAM
MARINE...Duke


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