626
FXUS63 KGRR 191543
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1043 AM EST Sun Jan 19 2020

LATEST UPDATE...
Update/Marine

.SYNOPSIS...
Issued at 314 AM EST Sun Jan 19 2020

- Inland lake effect snow tapers off early today

- Burst of snow by lakeshore today and along I-94 this afternoon

- Mainly dry weather Sunday night into Wednesday

- Chances for rain and snow the latter half of the work week

&&

.UPDATE...
Issued at 1042 AM EST Sun Jan 19 2020

Last portion of this one/two punch winter weather event is
underway. The first punch was the warm air advection snow Friday
night, the second was the lake effect last night into today. The
lake effect is in the process of winding down and will likely be
over for most of the area by 400pm this afternoon. The exception
will be along the I-94 where the snow may last into the late
afternoon for a bit. The snow is moving south along and ahead of a
cold front which is quickly changing the wind direction to out of
the north. The northerly flow will take the snow off shore and
out of the forecast area. Clearing is actually taking place across
Central Lower Michigan in the downsloping north wind regime.

The changes we made to Winter Weather Advisory were to end the
headline for areas north of I-96, essentially where the flow has
gone north already. Muskegon, Kent, Ionia and Ingham counties on
south are still in the advisory.

&&

.DISCUSSION...(Today through next Saturday)
Issued at 314 AM EST Sun Jan 19 2020

-- Inland lake effect snow tapers off early today --

No change to the previous forecast. We still expect a brief uptick
in lake effect snow early this morning followed by a gradual
decrease in coverage from east to west during the day.

Forecast reasoning: We are already seeing the beginnings of an
uptick with snowfall associated with the approach of another upper
PV max. The western edge of KGRR radar returns over Lake Michigan is
starting to creep westward, indicating a deepening layer of
convective instability with the synoptic lift. However, this is a
quick moving upper feature that will leave in its wake much lower
inversion heights and low level flow veering to become much more
lakeshore-parallel.

-- Burst of snow by lakeshore today and along I-94 this afternoon --

Continuing the previous discussion, we are increasingly concerned
about a snow burst pushing south mainly along the lakeshore.
Although short in duration, this could be highly disruptive and
there are indications its effects could be felt much farther inland
near the I-94 corridor around 2 pm this afternoon. Given that this
could be particularly impactful to travel, have extended the winter
weather advisory for our southeastern forecast area to cover this
scenario.

Forecast reasoning: This burst of snow will be associated with a
fast moving cold front dropping south during the day. Impressive
surface based convective instability is shown with this feature, and
this is being duly noted by snow squall parameter. This parameter
will be a good diagnostic to monitor on the SPC mesoanalysis page
today. Regarding significant inland penetration of the convective
instability, the NAM is aggressive as usual, but even the coarser
and more conservative GFS depicts this as well. Several convection
allowing models show a corresponding quick drop in visibility
associated with this narrow band extending all the way to Jackson.

-- Mainly dry weather Sunday night through Wednesday --

No changes to previous thinking and we see little indication that
this forecast will be subject to change.

-- Chances for rain and snow the latter half of the work week --

No change to previous thinking. Details on precipitation type
depends on the positioning of the associated surface low, which
still has limited predictability at the time range. Regardless, this
does not look to be an impactful system.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 641 AM EST Sun Jan 19 2020

There are indications we could see a brief but significant drop in
visibilities with a burst of wind and snow later today, chiefly
at the KAZO/KBTL/KJXN terminals along I-94. This is associated
with a sharp cold front moving rapidly southward across Southern
Lower Michigan. Attempted to represent this in TAFs with 1 hour
TEMPO groups, although any excursions into IFR would likely last
half an hour or less. Actual timing could easily be an hour or two
displaced from what is advertised. A similar brief intensification
is expected at KMKG, but with slightly earlier timing.

With the passage of this front, conditions improve markedly with
snow ending at most locations. MVFR/fuel alternate ceilings will
likely persist at most terminals into Monday morning, but some of
the inland locations such as KGRR and KLAN could very well lose
ceilings altogether.


&&

.MARINE...
Issued at 1142 PM EST Sun Jan 19 2020

Heavy Freezing Spray Warning and the Gale Warning have been
cancelled and we are down to a Small Craft Advisory and a
Lakeshore Flood Warning.

Waves will continue to decrease this afternoon and water levels
should begin to fall as well. The Lakeshore Flood headline will
likely be able to be dropped this afternoon ahead of the 7pm
expiration.


&&

.HYDROLOGY...
Issued at 415 AM EST Sun Jan 19 2020

... Re-inserting discussion from Saturday afternoon...

River Warnings remain at Comstock Park and Robinson TWP on the
Grand River. Comstock Park is falling and should fall below flood
stage Sunday night. Robinson TWP is holding steady and will likely
remain that way for at least the next couple of days. Water levels
on Lake Michigan certainly affect the lower end of the Grand River
at least to Robinson TWP. The push of wind and water tonight will
likely bring a rise in river levels from Robinson TWP downstream
to Lake Michigan. With cold and snow, river levels should fall in
most other areas, outside of ice jams.

Speaking of ice jams we will need to be on the lookout for them as
the colder weather settles in. River ice formation will commence
in earnest this evening as the cold air flows in. We already have
one ice jam of note on the Muskegon River just upstream of Rogers
Dam. At this point flooding has not been reported, but we have
issued a flood advisory for the potential for flooding as the
colder weather will likely increase the jam and potential back
water. We would not be surprised to see other ice jams form in the
coming days.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 1 PM EST this afternoon for
     MIZ056>058.

     Lakeshore Flood Warning until 7 PM EST this evening for MIZ037-
     043-050-056-064-071.

     Winter Weather Advisory until 7 PM EST this evening for
     MIZ064>067-071>074.

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

&&

$$

UPDATE...Duke
SYNOPSIS...TJT
DISCUSSION...TJT
AVIATION...TJT
HYDROLOGY...Duke
MARINE...TJT