Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 281147
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
647 AM EST Mon Nov 28 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 256 AM EST Mon Nov 28 2016

A deep low pressure system centered over the Upper Plains will
remain nearly stationary through Tuesday. This system will draw a
moist airmass into Lower Michigan resulting in occasional showers.
Gusty winds are forecasted as well. The system then tracks east
through the Great Lakes Region for the middle part of the week
drawing in a colder airmass. This will act to result in showery
weather here in Lower Michigan.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 256 AM EST Mon Nov 28 2016

The initial band of rain currently moving in from the west is
forecasted to slowly diminish due to the dry low level airmass
that is in place here in the CWA. Still enough momentum with this
band of rain to support higher POPs for early this am. Then a lull
in the precipitation is expected for the middle part of the day.

Models are in decent agreement in developing a wave of low
pressure upstream in the Middle MS Valley this afternoon. This
feature then tracks northeast through Lower MI later this
afternoon and into the evening. This system is expected to spread
numerous showers into the CWA. Locally heavy rain...gusty winds
and perhaps an isolated thunderstorm are possible. We will need to
monitor the 06z to 09z Tue period for possible enhanced wind
gusts...especially Kalamazoo to Jackson an up to Lansing area. The
low level jet does increase at this time and some weakness in the
surface stability is seen. If an organized line of showers could
get going...gusts over 40 mph would be possible. Then the mid
level dry slot moves in and is expected to rapidly diminish the
precipitation from southwest to northeast through the CWA 09z to
12z Tue.

Models are now trying to develop yet another mid level wave over
MI Tuesday evening. I will feature scattered showers for this
potential system.

.LONG TERM...(Wednesday night through Sunday)
Issued at 256 AM EST Mon Nov 28 2016

The general pattern for much of the long term remains unchanged with
cooler and unsettled weather expected. The details remain uncertain,
with exact pcpn timing/placement/type still yet to be ironed out.

We will be seeing the colder air pushing in across the area at the
beginning of the long term on Wed night. This will occur as the
center of the low starts to exit the area, and the colder air wraps
in behind it. This colder air is not significant by early December
standards. It will be cold enough that pcpn could start
mixing with/change over to a little snow.

Occasional rain and snow showers will eventually change over to
mainly snow showers by the weekend as additional colder air comes
in. The cyclonic flow will hold in place until Sat, allowing short
waves to move through and a lake effect influence to help pcpn chcs.
This should diminish late Sat as ridging builds in for a short time.

We are looking at another system potentially impacting the area as
early as Sun. There is a lot of uncertainty about the evolution and
strength of this system. We will keep a chc of pcpn in the fcst for
Sun for now, and watch future trends.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 641 AM EST Mon Nov 28 2016

Lower clouds and visibilities will be arriving as the day
progresses leading to impacts at the TAF sites. IFR looks likely
by the afternoon or evening as the low level moisture increases
and rain returns. In addition...gusty winds are expected...with
values over 25 knot by the evening. Local wind gusts over 35 knots
are possible later tonight. The wind will shift to the southwest
later tonight. At that time ceilings may improve somewhat.

&&

.MARINE...
Issued at 256 AM EST Mon Nov 28 2016

Hazardous boating conditions are forecasted into the middle part
of the week as a powerful storm winds up over the Northern Plains.
The winds could approach gale force at times into Tuesday. Will
maintain the high end Small Craft Advisory given these conditions
are expected to prevail for the period. Will need to monitor
trends closely as any increase in the mixing could certainly lead
to a period of gales.


&&

.HYDROLOGY...
Issued at 305 PM EST Sun Nov 27 2016

The latest 48 hour QPF being used for the RFC forecasts would bring
a few forecast points above bankfull if all the rain materializes.
This would include the Grand River at Ionia, Maple River at Maple
Rapids, Looking Glass River at Eagle, and the Sycamore Creek at
Holt. Trends will be monitored with future river forecast updates.
This rain would likely boost numerous locations from the 70th and
80th percentiles to perhaps the 90th percentile or even max for this
time of year, compared to climatology. That said, significant
flooding looks quite unlikely. In general, expect river rises within
banks for many locations and perhaps out of banks for the harder hit
areas.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 AM EST Tuesday for LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...NJJ
AVIATION...MJS
HYDROLOGY...Hoving
MARINE...MJS



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