Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 120233
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
933 PM EST Wed Jan 11 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 330 PM EST Wed Jan 11 2017

A low pressure system will move through the Great Lakes region
tonight and bring a wintry mix of precipitation. Fair weather
will return late Thursday through Friday as a high pressure ridge
builds in. Cooler temperatures will briefly return Friday into
Saturday before a moderating trend of temperatures occurs again
late in the weekend into next week.

&&

.UPDATE...
Issued at 933 PM EST Wed Jan 11 2017

The update this evening was mainly to freshen up the pcpn trends,
and add some drizzle/freezing drizzle to the fcst. The headline
remains the same for now.

The event has been going down pretty much as expected thus far.
P-type has been mainly rain for the Srn half of the area, with a
band of sleet and freezing rain, and then mainly snow toward
Ludington.

We are seeing the back edge of this pcpn starting to approach the
area from Lake Michigan. This feature is like a dry slot, with
the deeper mid/upper level moisture pulling away. We are expecting
that pcpn will likely go over to some drizzle/freezing drizzle
(depending on local temp) as most of the area loses the DGZ over
the next couple of hours and low level moisture/lift remains
sufficient.

We will need to monitor just how much the drizzle/freezing drizzle
becomes a factor. If areas like GRR can fall below freezing and
keep the drizzle, this would cause some impacts. The headline
would then need to be expanded.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 330 PM EST Wed Jan 11 2017

Primary short term fcst concerns involve determining potential for
snow/freezing rain late today through tonight into Thursday.

A consensus of latest short range guidance suggests that light
snow will develop across our northern fcst area late this
afternoon and evening as a 1000 mb low currently over northern
Missouri moves northeast to near Toronto by 06Z. Snow
accumulations of around an inch or two are expected across our far
northern fcst area tonight with locally higher amounts to 3 inches
possible.

A polling of 12Z model fcst soundings and higher resolution short
range/sref probabilistic guidance all suggest that pcpn from
around KMKG/KLDM ene to KRQB/KMOP will become mixed with or change
over to a several hour period of fzra this evening. Up to a tenth
of an inch of ice accumulation is possible. For the aforementioned
reasons which will result in hazardous travel conditions we have
issued a winter wx advisory for most of our northern fcst area.
Thx for coord on fcst/headline decisions APX/DTX.

Near to south of I-96 we expect rain to develop tonight. Pcpn
along the I-96 corridor may become mixed with or changeover to
a very brief period of sleet or very light freezing rain just prior
to ending prior to daybreak. Isolated convection should stay
south/se of our area tonight as we do not believe there will be
sufficient enough instability or forcing for convective initiation
to occur.

Tranquil wx will return beginning Thursday afternoon through
Friday as a high pressure ridge builds in.

.LONG TERM...(Saturday through Wednesday)
Issued at 330 PM EST Wed Jan 11 2017

A zonal flow upper pattern is in place throughout the long term. The
zonal flow of air will lead above normal temperatures during the
long term period. We are looking at highs in the 30s over the
weekend with readings pushing into the 40s early to mid next week.

There is one main feature to key on in the long term and that is a
cut off low that is forecast to be over the Baja of California
Saturday morning. The upper low pivots to the Texas panhandle Sunday
evening and is forecast to move into the western Great Lakes early
next week. This low will bring a southerly push of warmer air into
our region.

Surface high pressure will keep the weekend dry it appears for the
most part. We may see a little light snow late Sunday night on the
initial fringes of the precipitation shield of the low lifting north
through the plains. The bulk of the precipitation is expected on
Monday and Tuesday as the low moves northward near Lake Michigan.
850mb temperatures from 12z Monday into Tuesday evening, the main
time frame of precipitation, are above 0 C. Both the operational
ECMWF and GFS have us pushing towards +8C, so it mainly looks like a
rain event outside of some light snow mixing in possible on the lead
edge.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 654 PM EST Wed Jan 11 2017

Low cigs and vsbys came in quickly late this afternoon as the
pcpn developed quickly overhead. Now that the lower conditions
have moved in, they are expected to persist well into Thursday.

Rain will persist at the terminals through about 05z or so, give
or take an hour or two. KGRR and KMKG will have a chance of seeing
pcpn end as some light freezing rain, if the temps can drop below
freezing before it ends. We do think that some freezing drizzle
will be possible even after the rain ends at KGRR and KMKG. The
other sites seem like temps will remain warm enough that it would
be just drizzle. Once moisture deepens a bit near KMKG, they may
see some light snow on Thu.

LIFR-VLIFR conditions will likely persist all night across the
area. We expect that there will be slow improvement starting
toward 16z on Thu or so, with better improvement after 21z.


&&

.MARINE...
Issued at 330 PM EST Wed Jan 11 2017

A small craft advisory remains in effect through early this
evening. Wind speeds and wave heights will subside somewhat this
evening and overnight.


&&

.HYDROLOGY...
Issued at 330 PM EST Wed Jan 11 2017

Rivers are running above normal across the area due to rain, melting
snow and ice jams. The Looking Glass River at Eagle and the Grand
River at Comstock Park have warnings active, as they are expected to
reach flood stage. A watch is out on the Grand River at Robinson
Township due to ice jam potential. Multiple sites also have
advisories active. A period of colder than normal temperatures today
through the weekend may allow river ice to redevelop.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EST Thursday for MIZ037>040-
     043>046-050-051.

LM...None.
&&

$$

UPDATE...NJJ
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Duke
AVIATION...NJJ
HYDROLOGY...63
MARINE...Laurens



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