Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 142341
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
641 PM EST Thu Dec 14 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EST Thu Dec 14 2017

Another cold front will sweep through the Great Lakes Region late
tonight and early friday, bringing more lake effect snow showers.
Reduced visibilities and slippery roads will impact the Friday
morning commute over western lower Michigan. Some additional light
snow is expected Friday night into early Saturday with a warm
front, then temperatures will moderate above freezing Sunday
into early next week.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 330 PM EST Thu Dec 14 2017

Have issued a Winter Weather Advisory for lake effect snow for
late tonight and Friday for the western two tiers of counties
minus Van Buren and Kalamazoo. Have left these two counties out
of the advisory since winds for the first six hours of the event
are southwesterly.

Next shortwave diving southeast through the area triggers a quick
hitting lake effect event late tonight into midday Friday. Total
accumulations of generally 2-4 inches expected, with heaviest snow
showers expected during the morning commute time as sfc cold
frontal passage and hence best sfc convergence is occurring.

Guidance suggests that the more intense snow showers may be
displaced just inland from the Lk MI shoreline, closer to Hwy 131.
This is due to the strong westerly winds coming off the lake and
pushing the best surface convergence farther inland. Thus some of
the coastal communities such as Muskegon and Holland may be on
the lower side, with higher amounts focused more toward Grand
Rapids and Big Rapids.

Diminishing trend anticipated after midday Friday as upper trough
begins to lift out. Stronger winds during the afternoon may
produce some areas of blowing snow, and also send the snow
showers much farther inland. Guidance indicates best coverage of
snow showers on Friday afternoon will be near and south of I96.

Another quick burst of 1-3" snowfall possible Friday night into
early Saturday as band of isentropic lift snow breaks out
ahead/north of apchg warm front. This may be enhanced at the onset
by sw flow lake effect.

.LONG TERM...(Sunday through Thursday)
Issued at 330 PM EST Thu Dec 14 2017

Active weather pattern continues with couple of storms in the
extended and some lake effect snow showers.

Southern stream moisture makes a run at Lower Michigan on Sunday but
the northern stream remains well separated and it appears we may
miss out on much precip as the northern stream is dominant and the
sfc low passes well north of the forecast area. Cold front comes
through Monday night with cold advection and lake effect snow
showers Tuesday and Tuesday night then tapering off Wednesday as
warm advection begins ahead of the next low. Bumped up Superblend
POPs for lake effect snow showers during this time period.

Did not make any changes to Wednesday and Thursday as the 12Z GFS
guidance looks reasonable while the ECMWF has diverged to a more
amplified flow and deeper low...which looks to be overdone compared
to continuity. The less amplified GFS means a colder storm with
mostly snow while the ECMWF would be warmer with rain. The blend was
a compromise between the two, but leaning towards the GFS.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 634 PM EST Thu Dec 14 2017

Light snow was leading to some impacts to start the forecast
period. IFR occurring around KGRR...which appears to be localized.
Elsewhere MVFR or better ongoing. The snow should weaken somewhat
over the next hr or two...so I did trend KGRR up. Later tonight
the next wave of low pressure nears from the west with impacts
expected to develop during the morning. Snow will reduce the
visibility...especially for KGRR...KMKG and eventually KLAN.
The wind will also increase during the day...and gusts over 25
knots may occur during the afternoon.

&&

.MARINE...
Issued at 330 PM EST Thu Dec 14 2017

Next incoming cold front will kick up the lake again later
tonight and Friday with westerly flow increasing to 30 kts and
waves up to 8 feet. Will therefore reissue small craft advisories.


&&

.HYDROLOGY...
Issued at 330 PM EST Thu Dec 14 2017

Many rivers have iced over pretty quickly 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. Mild
temperatures early next week may 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 from 1 AM to 4 PM EST Friday for MIZ037-
     038-043-044-050-056-057-064-065.

LM...Small Craft Advisory until 5 AM EST Saturday for LMZ844>849.

&&

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...Ostuno
AVIATION...MJS
HYDROLOGY...CAS
MARINE...Meade



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