Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 161146
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
646 AM EST Sat Dec 16 2017

LATEST UPDATE...
Update/Aviation

.SYNOPSIS...
Issued at 310 AM EST Sat Dec 16 2017

Snow will end this Saturday morning and precipitation is not
expected again until later Sunday mainly south of I-94, most
likely as a mix of rain and snow. After Sunday, precipitation
isn`t expected again until the middle of next week. After another
cold day today, Sunday and most of the coming week will have
seasonal temperatures with highs in the 30s.

&&

.UPDATE...
Issued at 646 AM EST Sat Dec 16 2017

Snow is rapidly diminishing as indicated by models. Have made a
few cosmetic updates to the forecast to reflect this. IR satellite
imagery indicates a broad area of cold cloud tops upstream making
it questionable how much the DGZ will dry out. I have removed
freezing drizzle due to this uncertainty.


&&

.SHORT TERM...(Today through Monday)
Issued at 310 AM EST Sat Dec 16 2017

No changes planned to inherited forecast. Surface observations,
local VWPs, and radar indicate a convergent/frontogenetic pattern
underway centered roughly along I-96 with enhanced fgen
convergence from Grand Rapids to Lake Michigan as noted on KGRR
and KBIV observations.

IR imagery and short range model progs indicate some drying in
the DGZ later this morning which should allow snowfall rates
approaching 1 inch per hour to taper off rather quickly. This
rapid dropoff should occur around 7 AM, meaning that the current
advisory set to expire at 10 AM could possibly be cancelled
early. Would like to get a better feel for travel conditions
before making this decision however. There may be a brief period
of freezing drizzle as deeper moisture peels out, but additional
impact should be negligible with trace accumulations falling on a
substantial snow pack.

.LONG TERM...(Monday night through Friday)
Issued at 310 AM EST Sat Dec 16 2017

A cold front will bring potential for mixed light rain and light
snow showers Monday night into Tuesday that will end as a few light
snow showers and flurries as colder air filters in after fropa. A
high pressure ridge will then gradually build in from the west and
bring fair wx with seasonable temperatures Tuesday night through
Wednesday night.

The wx pattern will become more unsettled again late in the week as
an upper level trough digs and amplifies over the Great Lakes region
and a low pressure system moves through. expected again until the
middle of next week. After

There is still a considerable amount of uncertainty in 00z medium
range guidance concerning the eventual track/strength/timing of that
low pressure system late in the week. However an overall guidance
consensus does show potential for accumulating snowfall Thursday
into Friday particularly over our northern fcst area where thermal
profiles will be colder.

Beyond that medium range guidance consensus suggests that it will
turn colder next weekend as the upper level trough continues to dig
and amplify over the eastern CONUS. Even colder arctic air may
potentially be on the way. It is noted that the 00z ecmwf suggests
h8 temps could fall to around -25 C by Christmas Day. That would be
by far the coldest airmass of winter thus far.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 646 AM EST Sat Dec 16 2017

Expect temporary IFR restrictions to visibility in snow to
briefly affect AZO...BTL...LAN terminals early this morning.
Otherwise, we expect a gradual transition from IFR ceilings before
18Z to fuel alternate MVFR ceilings areawide through 00Z this
evening. Winds will shift to east-northeast and become light during
the day.


&&

.MARINE...
Issued at 310 AM EST Sat Dec 16 2017

Current trends and WaveWatch3 guidance indicate we can safely
cancel the small craft advisory. Localized strong onshore winds
likely aided by frontogenesis will reverse to light offshore later
this morning as a surface front drops south. This will allow
waves to diminish rather quickly. Waves will ramp up once again
late Monday with strengthening onshore winds.


&&

.HYDROLOGY...
Issued at 322 PM EST Fri Dec 15 2017

Many rivers have iced over due to the snow and cold temperatures.
The Looking Glass near Eagle has risen above bankfull due to
downstream ice constricting the flow. It is expected to gradually
fall but some fluctuations are still possible. High temperatures
above freezing early next week will soften the ice a bit. Water
frozen in the snowpack ranges from 0.5 to 1 inch in most locations,
but a full snowmelt is not expected anytime soon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EST this morning for MIZ050-
     051-056>059-064>067.

LM...None.
&&

$$

UPDATE...TJT
SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...Laurens
AVIATION...TJT
HYDROLOGY...CAS
MARINE...TJT



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