Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 210212
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
912 PM EST Sat Jan 20 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 327 PM EST Sat Jan 20 2018

After a quiet night, we will see more clouds and drizzle by Sunday.
A steady rain will develop into Sunday night and last into Monday
night. As one heads north into Central Lower Michigan a wintry mix
can be expected.  A light accumulation of snow and ice is expected
Sunday night into Monday morning, before the precipitation changes
to all rain there by Monday afternoon.  Some travel issues may be
seen in places like Ludington, Evart and Mt. Pleasant Sunday night
and Monday morning.  After steady rains Monday and Monday evening,
colder air returns, and many areas will see a switch to snow late
Monday night.

The snow is expected to continue into Tuesday with some minor
accumulations.  Quieter weather should be seen by Tuesday night and
last through Friday.  Then more rain or snow is possible again by
Friday night into Saturday.

It will stay mild through Monday, then colder temperatures are
expected Tuesday through Thursday.  Another warm up appears by
Friday and Saturday.

&&

.UPDATE...
Issued at 911 PM EST Sat Jan 20 2018

Leading edge of the stratus (overcast skies) has inched up to
I-94 and is expected to spread slowly northward overnight. Partly
cloudy skies with only thin cirrus north of the stratus deck
tonight, with a risk of patchy radiation fog developing due to the
light winds and recent snowmelt. Also there could be some drizzle
and fog breaking out late tonight near I-94 as ceilings of the
stratus deck continue to lower.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 327 PM EST Sat Jan 20 2018

The northern row of counties, and even Mecosta and Isabella Counties
will begin to see a wintry mix Sunday night into Monday, with the
possibility of needing headlines there.  Elsewhere a steady rain
will develop by late Sunday night and continues into Monday evening.
Some hydro issues will be possible.  The rain will change to snow in
most places late Monday night.

A patch of stratus was over portions of IA, MO and IL.  These clouds
will expand into Lower MI late tonight and include the entire CWA by
mid Sunday morning.  Expect areas of drizzle will break out too,
mainly into the afternoon, along with fog.  The fog should become
widespread, and locally dense Sunday afternoon and should linger
into Monday evening.

Main pcpn event really doesn`t start until Sunday night, mainly
late. By then we will see a front slowly sag south through the CWA,
with low pressure near Kansas City pumping deeper Gulf moisture into
the Great Lakes.  Expect a surge of rain will move in between 06Z
and 12Z on the heels of a low level jet.  The rain continues into
Monday morning, then a dry slot will pass through late afternoon and
evening, before the wrap around moisture brings more rain later
Monday evening.  All told expect many areas to see around an inch of
QPF.

Regarding the northern portion of the CWA, a wintry mix will likely
occur across the Highway 10 corridor, as well as Mecosta and
Isabella Counties.  Early on Sunday night, freezing rain is the most
likely pcpn type, but some rain and snow will mix in.  Some light
snow accumulation of less than an inch is possible.  Then by late
Sunday night the warm surge will cause a mix of freezing rain and
rain.  It appears Osceola and Clare Counties stand the best chance
to see a prolong period of freezing rain and over a tenth of an inch
of ice will be possible there.  All areas switch to plain rain into
late Monday morning.  Headlines will be possible for this region,
with the main impacts late Sunday night and Monday morning.

As the low pressure moves over MI and then to the east, colder air
will wrap in late Monday night, switching the rain to snow.  Little
to no accumulation is expected however through 12Z Tuesday.

.LONG TERM...(Tuesday through Saturday)
Issued at 327 PM EST Sat Jan 20 2018

The long term will have a 1 to 3 inch snow event Tuesday, as the
cold air comes back in. Another shortwave with more cold air will
likely cause more snow showers Wednesday into Thursday but snowfall
amounts will be light. A warming trend sets in for Friday and
Saturday.

As I mentioned yesterday we have a rather robust MJO going on and
that has forced the southern stream to dominate the weather patten
for the CONUS and it will likely remain so for at least 2 weeks
before we transition in week three back to a northern stream
dominated pattern. This does not mean we do not get any cold
weather, it just means the really cold air will remain north of this
area until the pattern shift in about 3 weeks. So, till then the
northern branch of the polar jet will largely stay north of here.
Even so, as large scale shortwaves move though, some cold air will
be brought south, which is why Tue through Thu temperatures will
average near normal.

As far as day to day weather, Tuesday we have the upper level cold
pool moving through the area bringing the cold air back. 850
temperatures fall to near -12c by evening. This will result in a
period of snow showers with lake shore areas seeing the most snow.
Actually it seems we get a deformation snow band on the northwest
side to the departing upper level low, enhanced by Lake Michigan
since low to mid level winds will be northwest during this time.
Temperatures will likely fall during the day Tuesday and I am
thinking this will be a 1 to 3 inch event.

Meanwhile another Pacific system, currently in the Gulf of Alaska
will be enhanced by a much stronger system, currently near the
Dateline. That will sharpen this upper level wave as it crosses the
Rockies then phases into the eastern Trough Wednesday into Thursday.
That will likely bring more light snow to the area, mostly lake
enhanced snow showers.  We could get a few more inches of snow from
this.

Once that is done, that next upstream Pacific system will be getting
close enough to the CONUS to push shortwave ridging into the area.
That will mean a slow warm up with dry weather Friday into Saturday.

.Week Two....(Sunday through Friday)

As I suggested yesterday, the next southern stream system will reach
the Great Lakes in the Sunday to Monday time frame. This will also
be a very wet system that could bring another inch or so of rain to
the area. Thunderstorms would not be out of the question. We will
still be in warm phase (for the eastern CONUS) of the MJO next week,
so even when the cold air comes in behind the Sun/Mon system it will
not be arctic cold, it will just like this week, bringing the
temperature back to normal after a warmer than normal period
Saturday into Monday.  It is worth noting some of the model runs of
both the GFS and ECMWF do suggest a wave on the cold front Monday.
This could mean a significant snow event if it happens since by then
we will be back in the cold air. Once again though, the cold air
will not last long as the next upstream Pacific system will push
more warm air this way. So, expect week two to also be warmer and
wetter than normal. This is in total agreement with the fastest
CPC forecasts Jan 27 through Feb 2.

It should be mentioned there is a very large pool of cold air over
Siberia, with 850 temps below -40C. Some surface temperatures have
been reported to be colder than 80 below this past week there.  This
pool of cold air will start coming over the North Pole in week two,
which sets us up for colder than normal conditions just beyond week
two as the MJO gets into a cold phase for the eastern CONUS.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 715 PM EST Sat Jan 20 2018

Confidence is fairly high that IFR or lower conditions due
to stratus/fog and drizzle will eventually develop across
southern lwr MI later tonight or Sunday. However the timing of
when that occurs is still a bit uncertain.

It is possible that some radiational fog will develop tonight
since the boundary layer is moist from melting snow and the winds
are light. However there is an area of stratus with MVFR bases
around 1500 ft currently spreading in from the south which should
prevent radiational fog development - at least south of
MKG/GRR/LAN.

Even if radiational fog is not a factor tonight (at least for
the I-94 corridor), the incoming area of MVFR stratus should
eventually lower to IFR levels when the warm front lifts north
toward the area Sunday, with fog/drizzle also lowering the vsbys
to IFR levels.


&&

.HYDROLOGY...
Issued at 225 PM EST Sat Jan 20 2018

A complete melting of the snowpack is expected Sunday/Monday in
the Grand, Kalamazoo, and lower Muskegon river basins. This will
release about a quarter to half inch of water. Rain totals on
Monday will probably range between 0.6 and 1.2 inches (ECMWF and
ensemble consistently lower than GFS and ensemble). Depth of
frozen soil varies but overall expect the ground to remain frozen
enough to allow efficient runoff.

A number of river forecast points will likely rise above bankfull
in the upcoming week. There is a chance of minor flood stage being
reached at a few sites (of earliest concern are Holt and Eagle),
particularly if higher rainfall totals verify. A breakup of river
ice is expected, and ice jams can cause local unpredictable
fluctuations in water levels. Road closures are possible in low
spots near river banks.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

UPDATE...Meade
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...WDM
AVIATION...Meade
HYDROLOGY...CAS


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