Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 110825
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
326 AM EST Sun Dec 11 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 326 AM EST Sun Dec 11 2016

Snow will continue today...moderate to heavy...as low pressure in
the Plains moves toward the Great Lakes. Total snowfall in the 6 to
10 inch range is expected.

A blast of arctic air will arrive mid week and result in highs in
the mid teens Wednesday and Thursday along with lake effect snow.
The below normal temperatures will continue through next weekend.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 326 AM EST Sun Dec 11 2016

Forecast concerns deal with the unfolding snow event and the current
headlines. There hasn`t been too much change in regard to the
dynamics of this system as it remains multi-faceted with both a lake
effect component and warm air advection component.

Latest radar shows snow ongoing across the cwa with a distinct lake
effect area moving north along the lake shore over Ottawa and
Muskegon counties. These counties along with Allegan will see
several inches of lake effect snow that will combine with the
ongoing warm advection to boost snow totals. After combining qpf
(which is a bit higher with the 06z model run) with model snow
ratios, snow totals around 10 inches are forecasted from Muskegon
county south through Van Buren and 9 inch totals from Kent southeast
through Ingham. For consistency with surrounding offices, we
upgraded the advisory to a winter storm warning mainly along and
south of I-96. The heaviest snow will fall in this area from 14z
through 22z or so. Solid 3/4-1 inch/hr seems like a real possibility
given the strong isentropic lift at 285K. Strong pressure advection
was noted with 40kts perpendicular to the the pressure surfaces.
This snow will become increasingly wet as the day wears on due to
continued warm air flowing north into the system. Our cwa should
remain all snow though as we have fairly deep cold air in place. As
the snow becomes more moist, it will likely become more slippery too
creating bigger impacts.

The snow will begin to diminish later this evening as the low moves
east of the state. Mainly dry wx is expected Monday and a few
scattered lake effect snow showers possible Tuesday.

.LONG TERM...(Tuesday night through Saturday)
Issued at 326 AM EST Sun Dec 11 2016

We are looking at more unsettled and cold weather through the long
term portion of the forecast. We will see the next surge of arctic
air coming in just in time for the long term late Tue. Normally this
would ignite the lake effect and get it going strong. Indications
are right now that the sfc pattern will be a bit anti-cyclonic
immediately behind the front. We should see the low level flow
become more cyclonic through Wed, helping lake effect to get
started. As mentioned before, the degree of colder air and the flow
will have moisture depth fairly limited. The dgz will also be quite
low which will also likely limit the amount of lake effect.

The cyclonic flow aloft will lift out toward Friday, allowing a
brief break in the coldest of the air and lake effect. This will
eventually give way to a strong trough that is expected to be over
the Wrn states mid-week.This trough will eventually lift out, and
will likely develop a decent system and send it toward the region.
We are looking at least another burst of snow in the Fri/Sat time
frame. Models are even trying to bring warm enough air up from the
Gulf, that a mix will be a possibility.

As the storm moves through by late Sat, the area will become
entrenched under the upper low/cyclonic flow once again. This will
bring back the cold weather along with lake effect chances.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1245 AM EST Sun Dec 11 2016

This aviation fcst period will be one with lots of impacts through
most of the time in snow. Some lake effect has been crawling up
the coast over the past few hours, and is currently impacting KMKG
as of 0530Z with LIFR vsbys. Elsewhere, light snow is developing
from the SW with mainly MVFR and some IFR scattered around.

We will see the snow become more intense, and drive cigs and vsbys
down into the IFR and lower category by 15z most everywhere.
Conditions will remain down through most of the rest of the fcst
period at most of the sites. Some improvement could be seen at
KMKG late in the period, but should remain down through 06z
elsewhere.


&&

.MARINE...
Issued at 326 AM EST Sun Dec 11 2016

We extended the small craft advisory through Monday night. Winds and
waves will be hazardous for small craft during this time frame.

&&

.HYDROLOGY...
Issued at 129 PM EST Sat Dec 10 2016

The latest water temps on area rivers include the following
samples: 33 on the Muskegon River at Big Rapids, 34 on the
Kalamazoo River, and 35 on the Grand River at Eastmanville. Expect
rapid ice formation on these rivers starting the middle of this
upcoming week as air temps retreat into the teens and single
digits. Frazil ice development can occur quickly with these temps
combined with higher than normal flows. Snow also contributes to
ice development. In terms of ice jam potential, there is some risk
after ice develops given flows running on the higher side of
normal mainly for the Grand River basin. However, it is too early
to tell how much of a risk there is since the Grand River is
currently ice free. Residents in jam-prone areas should monitor
ice development over the course of the next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning until 4 AM EST Monday for MIZ050-056>058-
     064>067-071>074.

     Winter Weather Advisory until 4 AM EST Monday for MIZ037>040-
     043>046-051-052-059.

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

&&

$$

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


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