Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221650
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1150 AM EST Tue Jan 22 2019

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 325 AM EST Tue Jan 22 2019

- Wintry precipitation this afternoon and tonight with moderating
  temperatures

- Snow showers and colder air returns late week and for the weekend

- Potentially impactful snow next Monday

&&

.UPDATE...
Issued at 1114 AM EST Tue Jan 22 2019

Light precipitation was developing upstream across IL and now into
NRN Indiana. Based on forecast soundings and observations it looks
like there will be mixture of precipitation types at the onset
especially for the I94 corridor. Some of the latest data suggests
we may need to extend the end time of the headlines. This will be
addressed this afternoon as additional guidance was still coming
in.

&&

.DISCUSSION...(Today through next Monday)
Issued at 325 AM EST Tue Jan 22 2019

We are looking at a fairly active seven day period, and likely
beyond with a much more typical winter weather pattern settling in.

We will be making no changes to the ongoing winter weather headlines
issued yesterday for the system coming through later today. We
expect that precipitation will begin to arrive this afternoon,
having to overcome quite an initially dry air mass in place. We
could have some p-type issues right off the bat, especially for
areas south of I-96. The issues come from a limited depth of
moisture initially that could produce an unsaturated dgz. This could
lead to some light freezing drizzle at the onset, before
transitioning to snow as the dgz saturates, then to rain as enough
warm air advects in along and south of I-96 overnight.

The unsaturated dgz problems are much less likely further north as
moisture is sufficiently deep for nucleation, which will lead to
plain snow. Up there, it looks like a prolonged light snow event as
the warm air advection and deformation areas will both be in play.
This will lead to a few inches of snow over a 24 hour period or so.

A brief shot of cooler air will come in behind the Tue/Wed system,
but lake effect does not look to be a big player right away. A short
wave ridge will build in briefly, before another wave will approach
later on Thu. This will bring deeper moisture in, with sufficient
over lake instability already in place with 850 mb temps in the
negative mid teens C. Accumulating snow will be likely for SW flow
favored areas. Snow amounts should not get out of hand as the jet
core doesn`t really drop south of the area, and inversion heights
are limited as a result.

We will see colder air drop in then by Friday, with 850 mb temps
dropping below -20C. Sfc temps on Friday may be hard pressed to get
out of the single digits. Additional short waves will moving through
to help keep lake effect flowing. A stronger wave is expected to
dive just south of the state later on Friday. It could end up close
enough that southern areas could see some light accumulations of
system snow.

Another better clipper system will induce some snow, with lake
enhancement for SW flow favored areas Saturday night into Sunday.
Then another better system is expected to move in from the west
Sunday night into Monday as a longer wave trough dives into the
middle section of the country. This system has potential for a bit
more snow as Gulf moisture could get drawn into this, with cold air
still entrenched over the area.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 707 AM EST Tue Jan 22 2019

VFR conditions will be present this morning, but MVFR conditions
and an icing threat will spread in from west to east this
afternoon as a mixture of snow, sleet and freezing rain develops.

IFR will become widespread tonight with a variety of precipitation
types and icing continuing. The precipitation should become mostly
snow at MKG and GRR tonight, mostly rain at AZO/BTL/JXN after
midnight, remaining a mixture of snow and freezing rain at LAN.

Southeast sfc winds around 10 kts becoming south 10 to 20 kts
this afternoon. Sfc winds relaxing a bit tonight, although
southwest winds of 40-60 kts expected 2-6K ft AGL resulting in a
LLWS threat.


&&

.MARINE...
Issued at 325 AM EST Tue Jan 22 2019

We will be leaving the Small Craft Advisory and Heavy Freezing Spray
warning as is this morning. Winds over the water ahead of the next
system are fairly solid this morning, and will remain so for the
foreseeable future. We will likely need an advisory for quite a
period. Heavy Freezing Spray will remain likely early today with the
cold air remaining in place for the time being. Warmer air
moving in will temporarily end this threat later today.

Much of the next seven days will likely see advisory conditions. As
arctic air moves back in for the end of the week, heavy freezing
spray will become likely once again. A good deal of ice is expected
to develop.


&&

.HYDROLOGY...
Issued at 316 PM EST Mon Jan 21 2019

Very cold temperatures will persist through Tuesday morning, before
we see a brief warm up for the middle of the week. Freeze-up ice
jams will continue to be possible on rivers and streams tonight, and
may lead to rapid changes in water levels and localized flooding.
Currently, ice jams have been identified or highly suspected along
the Chippewa River near Mt Pleasant, the Flat River near Smyrna, and
the Looking Glass River near Eagle. No known flooding is occurring
at this time.

Warmer temperatures midweek will also arrive with our next chance
for precipitation. Light snow or a wintry mix is expected to spread
into the area Tuesday evening before changing to rain over the
southern Lower Michigan and continuing as snow over the northern
half of Lower Michigan. The exact line between rain and snow is
still a little challenging to predict, but will delineate where rain
and melted snow run into the river system and where water remains
locked in a building snowpack. The highest potential for rain will
be near and south of the I-96 corridor. Where precipitation falls as
rain the longest, we could see between 0.25 and 0.5 inches of water.
An estimated 0.2 to 0.8 inches of water equivalent lies in the
current snowpack over southwest Michigan, which could all melt over
the course of a few days where the rain falls. Runoff from rain and
melted snow may break up any ice jams that have formed, or could
possibly increase the risk for flooding if the river channel remains
blocked by ice and more water is added. Water levels will also rise
where we see rainfall, and a few of the smaller rivers and
tributaries may reach bankfull.

Temperatures will become very cold once again Thursday night through
Sunday as another blast of arctic air pushes into the region. This
will once again favor significant ice growth on rivers and bring the
threat for ice jams. We will also see several rounds of light
snow.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 1 AM EST Wednesday for MIZ056>059-
     064>067-071>074.

     Winter Weather Advisory until 10 AM EST Wednesday for MIZ037>040-
     043>046-050>052.

LM...Heavy Freezing Spray Warning until 1 PM EST this afternoon for
     LMZ844>849.

     Small Craft Advisory until 1 AM EST Thursday for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...NJJ
DISCUSSION...NJJ
AVIATION...Meade
HYDROLOGY...HLO
MARINE...NJJ


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