Calm Weather Today – Midweek Storm — The Michigan Weather Center

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The weather will be calm today as it decides what to do tomorrow through Thursday as a large, messy storm system takes shape. There are no hazards, watches, advisories or warnings at this time, although we may see them later today. Below is the short-term discussion from the NWS Weather Forecast Center:

By Wednesday night and into Thursday, the aforementioned upper-level
trough is forecast to eject into the Southern Plains and spawn an area of
low pressure near the Texas Panhandle with an expanding precipitation
shield found toward the northeast. At the same time, a slow moving cold
front is anticipated to bisect the country from the Great Lakes to the
Southern Plains. The precise location of this cold front as it sinks
southward on Thursday will be crucial to determining which locations see
significant snow, rain, or a wintry mix. At the moment, the greatest
chances for disruptive snow extends from south-central Kansas through
central Missouri, northern Illinois, and into central Michigan. Areas of
sleet and freezing rain will likely be found just to the south of the
heaviest axis of snow, but rather high uncertainty remains regarding where
exactly the transition zone will set up. Residents are urged to stay tuned
to the latest forecast so quick preparations can be taken before the storm
begins.

Keep in mind these are just guesses at this point:

Confidence in the forecast increases for widespread snowfall on Thursday. Here are some main messages from this update. Predicted snow accumulations will be published in a later update. Besides snowfall, there is also a risk of river ice jams this week in southern Lower Michigan; please check for river updates in the coming days.

Forecast discussion

- Good deal of uncertainty remains for Wed-Thu System

Not much going on for today preceding the more potential noteworthy
event for Wed-Thu. Some lingering light snow showers continue this
morning for western areas. This is the result of sufficient over-
lake instability and a westerly component to the wind in the cloud
layer. These snow showers are expected to taper off as the flow
aloft becomes more southerly, and the sfc flow will be from the SE.
Some partial clearing is expected with the low clouds blowing out,
and lingering mid and high clouds holding in.

There is good consensus that there should not be many significant
impacts on Wed for the entire area, as pcpn should be all rain
during the daylight hours. Temperatures will be comfortably above
freezing as the rain develops overhead over the course of the day.
The only potential impact there could be hydrology related with the
rain and melting snow. We will address that more in the Hydrology
section below.

The uncertainty begins Wednesday night, and then continues through
the end of the event around Thursday evening. The uncertainty comes
in with regards to p-type and heaviest precipitation axis/p-type
amounts. The remaining uncertainty, and still a decent amount of
time before the impacts would arrive late Wed night/Thu morning will
keep us from issuing any watches at this time.

What is known is that we will see a gradual changeover of rain to a
wintry mix before going to all snow. This occurs as colder air is
drawn to the SE, and undercuts the warmer air aloft for some
uncertain amount of time. Many of the international models/ensembles
indicate that this window of mixed pcpn will be shorter, vs. a
longer potential in the american guidance. That then goes along with
where the heaviest pcpn axis ends up being. That is just another
layer of complexity.

The collaborated forecast will reflect somewhat of a middle of the
road scenario. That would be rain, changing to a little potential
freezing rain, then snow. The heaviest axis would be generally
across the southern half of Lower Michigan. Our thoughts of where
this might trend would be a little more to the south. We believe
that the further north solutions may be too far north for two
reasons. These reasons are there will be drier air feeding into the
area from the NE, and the further north solutions look to have the
mid level wave over-developed, which brings the sfc low a little bit
further north. The sfc low is only a part of the forcing, as this
event will be largely driven by a coupled upper jet scenario. This
system looks quite similar to the event from Feb 2nd, with the
difference being the presence of a mid level wave this time.

- Clipper system expected for later Friday

The pcpn will wind down quickly Thu evening, with a brief break in
pcpn Thu night and Fri morning. We will get back into the NW flow
once again, and a clipper will drop SE through the area. The brunt
of pcpn with that clipper will likely stay north of the area closer
to the core of the wave, with some light snow down here.

- Quiet and seasonable for the weekend and Monday

Once the late Fri/Fri night clipper moves east of the area, we
should see a fairly quiet and tranquil period through most of
Monday. The Polar jet retreats far enough North to keep the
unsettled weather up there. The upper flow off of the Pacific will
bring in a more mild air mass, vs the arctic from the North that has
dominated more recently.

Hydrology

We are monitoring two different concerns with regards to hydrology
with the upcoming system. The first will be snow melt and rainfall
on the front end of the upcoming system. Then the ice jam potential
aspect with the break up of ice with the up and down nature of the
temps along with runoff expected.

The good news is that the rivers are generally running around
normal, or even a little below normal over the Muskegon River basin.
This is good going into a melt/rain event like this. Much of the
area has less than 2 inches of water in the snowpack, with a little
over 2 inches toward the lakeshore. Much of this will probably melt
and run off with the ground frozen everywhere.

The good news is that new pcpn in the form of rain that would runoff
would be less than an inch. Heaviest amounts likely further south.
With rivers running at or below normal, they should be able to
handle this. A good chunk of the pcpn will come as snow, which will
not add to the runoff at this time.

The uncertain part of this is the ice jam part. There is not a lot
of ice on the Kalamazoo River, so there is less of a threat there.
The Grand and Muskegon basins do have more ice, and could end up
breaking up. Then it all comes down to how much breaks up, and then
hangs up in the typical areas. We will continue to monitor this, but
there is not a significant concern for now.

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