Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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154
FXUS63 KGRR 101131
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
631 AM EST Sat Dec 10 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EST Sat Dec 10 2016

We`re in the middle of a snowy period that will last through much of
next week. An incoming storm is poised to produce 8 to 10 inches of
snow later tonight through early Monday. An arctic airmass will
arrive the middle of next week and bring the coldest air of the
season...and more lake effect snow.

&&

.SHORT TERM...(Today through Monday)
Issued at 328 AM EST Sat Dec 10 2016

Forecast concerns deal with the approaching storm later tonight
through early Monday. A winter weather advisory has been issued for
tonight through early Monday.

The models have been pretty consistent in showing a developing low
in the Plains moving northeast across Michigan late Sunday. Much of
the early portion of the storm is isentropic lift related and those
situations are always a bit dicey in that they sometimes don`t
always go as planned. But the basic setup is consistent. Moisture
content and dynamics with the latest model runs are similar to
previous runs and so confidence is fairly high on this event.

The initial component of the storm will being this evening as
isentropic lift commences and saturates the column. The southwest
flow ahead of the low will also produce some lake effect as h8 temps
remain rather cold at -14c and thus over-lake instability remains
high. So instead of waiting for the isentropic pcpn to develop,
we`ll likely see lake effect develop in the southwest flow, and then
that will be aided by the isentropic properties later tonight.

The strongest dynamics will occur Sunday when pressure advection is
maxed and uvv`s are greatest. Accums in the 4 to 6 inch range seem
plausible Sunday to go along with 2 to 3 inches tonight. Another 1-3
inches are possible Sunday evening as the storm begins to wind down.

We`re forecasting a total event in the 6 to 10 (or so) range over a
period of 30 hours from this evening through around 4am Monday.
Highest totals will be over the west central CWA where we see a
boost from the southwest lake effect in advance of the main low.

This could turn into a wetter snow than we`ve seen in the past few
days as moisture content will be higher and so will the
temperatures.

.LONG TERM...(Monday night through Friday)
Issued at 328 AM EST Sat Dec 10 2016

Very cold air is poised to move into Lower Michigan Tuesday through
the rest of next week. Light lake-effect snow showers will be common.

There is a chance for light snow associated with the arctic front
Monday night into early Tuesday, especially across the northern half
of the forecast area. Deeper moisture will be present further north,
closer to the parent low. A shortwave moving through Monday night
will help to provide some lift. The DGZ is saturated with some lift,
so some light snow seems like a good bet. But QPF and accumulations
will remain light.

A non-diurnal trend seems likely on Tuesday with CAA well underway.
Highs should top out early in the day in the mid 20s. Lows Tuesday
night will likely drop into the teens for most, but the northern CWA
could see single digits. Wednesday through Friday will be very cold,
with highs generally in the teens to around 20 degrees. Lows in the
single digits should be common Wednesday night and Thursday night.
Persistent, light lake-effect looks likely from Tuesday on next
week, especially near and west of US-131. Accumulations will be held
in check due to a DGZ near the ground.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 630 AM EST Sat Dec 10 2016

Lake effect snow showers will spread inland a bit today due to
westerly boundary layer winds. Steady snow will develop this
evening as a storm in the Plains moves toward the lower Great
Lakes. Several inches snow is expected at the taf sites from this
evening through early Monday.

&&

.MARINE...
Issued at 328 AM EST Sat Dec 10 2016

We extended the small craft advisory through Sunday night as the
next storm rolls through the Great Lakes. For the most part, winds
and wave will be hazardous for small craft.


&&

.HYDROLOGY...
Issued at 203 PM EST Fri Dec 9 2016

The primary focus will be on river ice development into next week.
At this point it appears conditions will be very conducive to
frazil ice development, and it could occur quickly after the
Arctic front passes through. You need mean daily temperatures to
be 20 degrees or colder to promote an increase in thickness of
river ice. This will occur starting mid week. So, river ice could
form once temperatures plunge and the threat is there for rapid
growth after it initially forms. Near to above normal river flows
are favorable for increased frazil ice development coupled with
Arctic air.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 10 PM this evening to 4 AM EST
     Monday for MIZ037>040-043>046-050>052-056>059-064>067-
     071>074.

LM...Small Craft Advisory until 7 AM EST Monday for LMZ844>849.

&&

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...EBW
AVIATION...04
HYDROLOGY...Hoving
MARINE...EBW



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