Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 092028
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
328 PM EST Mon Jan 9 2017

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

.SYNOPSIS...
Issued at 328 PM EST Mon Jan 9 2017

A winter storm system from the Central Plains will deepen rapidly
tonight as it heads for the northern Great Lakes Tuesday
afternoon. This will put southwest Michigan in the warm sector of
the storm ending our week of cold and snowy weather. However
before that as the warm air surges in tonight expect snow to
develop by late evening and it may be heavy at times overnight
north of Grand Rapids. The snow will change to rain from south to
north Tuesday morning. Expect breezy conditions, periods of rain
Tuesday afternoon with temperatures near 40. The cold front comes
through Tuesday night but it does not get far as another system
track through the Great Lakes Wednesday night into Thursday. This
is expected to bring freezing rain to northern area and more rain
to Central and southern areas.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 328 PM EST Mon Jan 9 2017

One more snow storm before a January thaw moves in and for the
most part last at least 2 weeks. We can thanks some major changes
in the hemisphere upper wave pattern for this. First there is
another East Asian Jet feature that crosses the Pacific. That
feature helps to cause the polar low to retread back to the north
pole. This all causes a more zonal upper air pattern that will
keep the real arctic air away for at least 2 weeks.

So for this to happen, as is typical we need a strong storm from
the central plains to transition us into the warmer air. This
system is developing over over Wyoming at 2 pm and will track
across upper Michigan Tuesday. This allows for a strong surge of
Gulf moisture north into Michigan tonight into Tuesday. There has
been some model disagreement on when the transition to rain will
be but actually the models have come into better agreement. Most
of the significant snow will fall between midnight and sunrise
over more of our CWA. The rain to snow line should reach I-94 well
before sunrise and to Route 10 by noon or so. That being so I
split the winter weather advisory into 3 sections to allow better
timing of the transition from snow to rain. Since northern areas
will be snow longer, there will be more snow up there.

This system departs quickly to we get onto the cold air for only
12 hours Tuesday night into early Wednesday. The upper wave from
the North Pole runs into the southern stream Wednesday and that
causes a wave on the front that brings more rain to the area
Wednesday night into Thursday.

.LONG TERM...(Thursday through Monday)
Issued at 328 PM EST Mon Jan 9 2017

Longer range model output is in agreement showing modified arctic
air over the region later Thursday into Saturday...with a moderating
trend into early next week.  Main forecast challenge will be
precipitation type as we waffle back and forth near critical
thickness values in the active weather pattern.

Precipitation will be ongoing Thursday along the leading edge of the
colder air.  Expect to see a change to snow as the system
departs...but precipitation amounts should be light.  Another fast
moving disturbance will bring a chance for light precipitation
Saturday.

A stronger wave develops over Texas on Sunday and moves into
Michigan by Monday. Current thinking is that snow will prevail on
Sunday... changing over to rain on Monday as warmer air approaches.
There are differences in the model output which could change the
precipitation type.

The coldest temperatures are expected Friday into Saturday
morning...with single digit lows possible in northern sections
around sunrise Saturday.  A warming trend is then expected in
advance of the system for Sunday into Monday...with temperatures
approaching 40 on Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1226 PM EST Mon Jan 9 2017

KGRR 88D was indicating area of light snow over west Michigan
this morning. While the early trend was for the snow area to move
east...a northerly component developed over the past few hours to
the southwest of KGRR...which kept light snow and lower visibilities
going longer than originally expected. This area has been shrinking
in size over the past hour or so...and will end the snow early this
afternoon at KGRR. Remaining TAFs will by dry with ceilings from
2-3kft this afternoon.

The dry weather will be short lived as another system brings mixed
precipitation back into the area late this evening into Tuesday.
Snow will be the primary precipitation type this evening...with a
change from snow to freezing rain around around sunrise...and then
to all rain Tuesday morning. Expect a faster transition to rain at
TAF sites along I-94 as the southerly wind brings moisture and
warmer temperatures to the north.


&&

.MARINE...
Issued at 328 PM EST Mon Jan 9 2017

I issued a Gale Warning for tomorrow evening into early Wednesday
morning. The short period for this is due to the quick movement of
this storm system.

&&

.HYDROLOGY...
Issued at 1140 AM EST Sun Jan 8 2017

Concerns continue in regards to ice jam potential, as several
sites have shown/still show the affects of ice development.

Most susceptible sites up to this point have been smaller streams
and rivers with frequent, sharp bends. The Looking Glass River
near Eagle and Flat River near Smyrna are two sites of higher
priority. Fortunately, most recent data out of these two points
shows both sites may have reached a peak and are beginning to
fall. In addition, yesterday`s concern on the Grand River near
Robinson Twp and Eastmanville subsided for now. Both sites seem to
have stabilized for the time being.

This has been common behavior over the last two days. Once
river/stream flows exceed the ability for ice to hold back water,
the jam either breaks or levels stabilize.

Despite any impression of stabilizing, rivers will continue to
demand attention. As has been mentioned in previous discussions,
the pattern remains active next week with moderating temperatures.
Precipitation amounts late Monday through Tuesday are forecast to
total somewhere around 0.75 inches. A frozen ground layer will act
to quickly distribute any snowmelt and/or rainfall to area
rivers. While there are never any guarantees, the combination of
milder air, existing ice and elevated river levels may result in
flooding through at least mid-week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 1 AM to 10 AM EST Tuesday for
     MIZ064>067-071>074.

     Winter Weather Advisory from 1 AM to 7 PM EST Tuesday for
     MIZ037>040-043>046.

     Winter Weather Advisory from 1 AM to 2 PM EST Tuesday for
     MIZ050>052-056>059.

LM...Small Craft Advisory until 5 PM EST Tuesday for LMZ844>849.

     Gale Warning from 5 PM Tuesday to 7 AM EST Wednesday for
     LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...MWS
AVIATION...MWS
HYDROLOGY...JAM
MARINE...WDM



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