Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 211205
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
705 AM EST Mon Jan 21 2019

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Mon Jan 21 2019

- Cold Wind Chills occurring this morning

- Next system to bring a wintry mix/snow Tuesday into Wednesday

- Bitter cold air surges in behind Arctic Cold front Thursday

- Lake effect snow expected Thursday night through weekend

&&

.DISCUSSION...(Today through next Sunday)
Issued at 330 AM EST Mon Jan 21 2019

Ongoing wind chill event is occurring about as expected. Air
temperatures at all of the observing sites in the area are below
zero as of 300 AM. The coldest temperature at the present time is at
one of the traditionally colder sites, the Baldwin fire weather ob
site, at -18F. Winds are light in most areas, at or less than 5
knots and this will likely continue to be the case per the HRRR
surface wind forecast. Plenty of cooling to go yet tonight with
another 5 hours of darkness (sunrise just after 800 AM). Coldest
wind chills are where there is just a bit of wind at Alma and
Lansing. Both are indicating a wind chill right around -20F. Will
let the headline stand as is with no changes, continuing through
noon today.

The main item in the forecast to deal with is the system moving into
the area on Tuesday. The system is associated with the upper trough
seen moving ashore in California this morning in water vapor
imagery. The system moves through the Rockies tonight and emerges
into the plain on Tuesday. There are some model differences on how
the system evolves as it moves our direction. The ECMWF is slower,
with all of the models taking a slightly different track across the
area with the surface low. The GFS is further north and introduces a
bit more of a mix. At this point we have used a compromise of the
models and are in line with our previous forecasts. We are still
expecting mainly snow across Central Lower Michigan where we may see
3-6 inches of snow. A mix is expected in the far south, especially
along I-94. A few inches of accumulation is expected along I-96 as
well with the potential for a mix as well. At this point want to see
a bit more consistency in the models before issuing a headline but
it is looking like we will need one for the mix south and the snow
to the north.

The cold front poised to move through on Thursday will be potent,
bringing in a surge of Arctic air. -25C air at 850mb will be cold
enough to create travel issues where we see fine powdery lake effect
snows. Travel Thursday night into Friday towards Lake Michigan will
become difficult as salt will not be effective as temperatures
plummet.

Lake effect snows will become common in the wake of the Arctic
front, but as the prior forecast discussion noted, flake size will
be small. Persistent snows will occur down wind of Lake Michigan
although significant totals are probably not likely. Again, the
biggest concern will be travel issues with temps in the single
digits and below.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 705 AM EST Mon Jan 21 2019

VFR weather is expected the next 24 hours. Today, skies will be
mainly clear other than some high based cirrus clouds above
20,000ft. Tonight ceilings will lower into an altocumulus deck,
but even by morning bases should be at or above 7,000ft.
Winds will be under 10 knots today from the southeast.

&&

.MARINE...
Issued at 330 AM EST Mon Jan 21 2019

One Small Craft Advisory/Heavy Freezing Spray event has ended and
another is expected to begin this evening. We have ended the SCA and
Heavy Freezing Spray Warning that was in effect as winds and waves
have come down. Another event is expected from tonight into Tuesday
though. Winds and waves will peak late tonight and into Tuesday
morning. With temperatures in the teens F and winds in excess of 25
knots heavy freezing spray looks likely once again. The largest
waves will occur off shore with the winds being from the SSE.

Additional high waves are expected from Wednesday through Friday
behind the Tues/Wed system and again behind a cold front that will
surge through on Thursday.


&&

.HYDROLOGY...
Issued at 329 PM EST Sun Jan 20 2019

Very cold temperatures will persist through Tuesday morning and
will cause significant ice growth in rivers. Ice jams may form as
rivers freeze up, and may lead to rapid changes in water levels
and localized flooding. There is already a likely ice jam along
the Chippewa River west of the gauge site in Mt Pleasant, but
location is yet unknown and no flooding has been identified.
Other gauged rivers and streams are being monitored for
fluctuations in water levels. Temperatures will warm back into the
upper 20s to low 30s on Tuesday, and the low to mid 30s on
Wednesday. The warmer weather will also come with our next
widespread snow and rain event, which will raise water levels or
help break up any ice jams that form.

Precipitation should begin as snow Tuesday afternoon, then change to
a combination of a snow, a wintry mix and rain across West Michigan
Tuesday night and Wednesday. The best chance for rain will be along
and south of the I-96 corridor. The increase in water levels will be
minor for areas north of I-96 if little to no rain falls, as
moisture gets locked into a snow pack. Areas south of I-96 stand a
better chance of receiving between one-quarter and one-half inch of
rain. Runoff from the combination of rain and melting snow
(estimates of water in snowpack is between 0.2 and 0.5 inches) will
cause rivers to rise. We will start getting a better feel as to
whether any sites will reach/exceed bankfull tomorrow as river
forecast models take into account 48 hour QPF that includes this
system.

Precipitation for the remainder of the week will occur as several
light snow events. Temperatures will become very cold for the end of
the week, and will once again favor ice growth/regrowth.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Wind Chill Advisory until noon EST today for MIZ037>040-043>046-
     050>052-056>059-064>067-071>074.

LM...Heavy Freezing Spray Warning from 7 PM this evening to 1 PM EST
     Tuesday for LMZ844>849.

     Small Craft Advisory from 7 PM this evening to 1 PM EST Tuesday
     for LMZ844>849.

&&

$$

SYNOPSIS...Duke
DISCUSSION...Duke
AVIATION...Duke
HYDROLOGY...HLO
MARINE...Duke


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