Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 170911

Area Forecast Discussion
National Weather Service Marquette MI
411 AM EST Wed Jan 17 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 342 PM EST TUE JAN 16 2018

...Lake effect snow diminishes this evening, gusty winds overnight
through Wednesday...

The layout of lake effect snow has been quite complicated today as a
weak surface trough lingers across the eastern CWA and ridging
slowly builds across the western CWA. Moreover, LES activity became
increasingly cellular this afternoon in response to sheared low-
level flow and insolation. The wind shift ahead of the ridge was
located along a line from approximately Negaunee to Iron Mountain at
20UTC. Behind this line, light W to NW-wind lake effect will
continue into the evening. Ahead of this line, pockets of moderate
to heavy LES continue near Lake Superior. Given low visibility to
1/4mi and quick 1/2" to 1" accumulations under these showers, will
hold on to ongoing advisories for Marquette and Alger counties. As
WSW winds take hold later this evening, LES should shift northward
over Lake Superior. However, it would not be surprising to see a LES
band hug the shore of Keweenaw County or even possibly linger on
shore into the early overnight.

A weak trough embedded in larger mid-level troughing over northern
Quebec will brush NE Lake Superior overnight. Fairly dry low-levels
will prevent any precip, so only some mid-level clouds are expected.

Gusty winds and blowing snow will then be of some concern overnight
through Wednesday. W to WSW will increase overnight and remain gusty
through the day as Upper MI sits between a 1002hPa low over southern
Hudson Bay and a 1042hPa high over OK/AR. Though there will be a
substantial inversion around 2kft in response to robust WAA aloft,
dry conditions and 45-55kt winds on the inversion should translate
to very gusty conditions at the surface, especially with mostly
sunny skies during the day. With plenty of fresh, loose snow from
the past couple days, sharp reductions in visibility are expected
generally north of M-28 between Wakefield and Marquette, where gusts
of 30 to 35mph will be possible mid morning into the afternoon.
However, gusts to 40mph will be possible for westward facing slopes
of the Keweenaw Peninsula. Given this potential impact of briefly
very poor visibility during peak travel times Wednesday, have issued
an SPS for the aforementioned locations.

.LONG TERM...(Thursday through Tuesday)
Issued at 410 AM EST WED JAN 17 2018

...Potential winter storm is still on track for Sunday afternoon
through Tuesday...

The early portion of the extended forecast, Thursday through
Saturday, is set to be fairly quiet. There are a couple chances of
snow or rain/snow chances as shortwaves slide through the area and
temperatures steadily warm. The first shot of mainly light snow
would be Thursday as a stronger/fast moving shortwave slides through
the north half of the U.P. the best moisture/forcing will likely
stay north of the U.P.; however, the Keweenaw and locations along
Lake Superior could see a quick dusting of snow through the day
Thursday. Another wave is expected to slide through the area Friday
and again, the better forcing is expected to stay mainly over Lake
Superior. Not out of the question to see some rain/snow showers over
the Keweenaw.  That shortwave will likely produce mixed
precipitation as warmer air continues to advect northward on
southerly flow into the Upper Great Lakes. Actually, it looks like
high temperatures will warm above normal with upper 30s to near 40
degree readings possible Friday and Saturday.

Attention then turns to a potential winter storm for Sunday
afternoon possibly lingering through Tuesday morning. Models are in
good agreement on the track of the system, developing the low over
the Plains/mid Mississippi Valley Sunday morning, and then lifting
the low north and eastward into northern Lower Michigan. This would
be a very favorable track for heavy snow potential across central
and western Upper Michigan. The system would likely have plenty of
moisture to work with as the southerly flow is progged to be wide
open to the Gulf of Mexico moisture source. If this all works out as
each of the models are showing, there could be several inches of
snow across much of western and central Upper Michigan. The features
that would be responsible for this potential winter storm are well
outside of the more densely populated observation platforms, so it
is expected that the exact patch of the low and associated heaviest
snow band will vary over the next few days. Additionally, on the
east side of the low there will likely be some mixed precipitation
along with a potential dry slot, which will both have an impact on
snow totals. Again, confidence in forecasting this potential winter
storm will increase over the next couple days as the system is
better sampled. At this point, it will definitely be worth keeping
an eye on for the potential of widespread heavy snow Sunday
afternoon through Tuesday.

Tuesday and beyond, a consensus of the model blends was used. This
gives intermittent chance of lake effect snow; however, exact
placement will be dependent upon wind direction and placement of the
aforementioned stronger storm system.

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1142 PM EST TUE JAN 16 2018

Westerly winds will increase and become gusty through the morning
and afternoon hours at all TAF sites. These winds will allow blowing
snow given the fluffy nature of the recent snowfall, especially at
KCMX and KSAW where at times visibilities may drop down towards
MVFR/IFR category. Even though winds will be rather gusty at
times, model guidance still show very strong winds just off the
surface, with upwards of 45 to 55kt around 2000ft AGL. Therefore,
have maintained mentions of low-level wind shear. Winds will
gradually subside towards the end of this TAF period along with
any lingering visibility restrictions from blowing snow.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 342 PM EST TUE JAN 16 2018

W to WSW gales to 40 knots are expected to develop across western
Lake Superior overnight and eastern Lake Superior on Wednesday, then
diminish Wednesday evening. Heavy freezing spray is also expected
across the western lake during this time. Otherwise, no gales are
expected through the upcoming weekend.

Upper Michigan...
Lake Superior...
  Gale Warning until 7 PM EST this evening for LSZ267.

  Gale Warning until 10 PM EST this evening for LSZ265-266.

  Heavy Freezing Spray Warning until 11 AM EST /10 AM CST/ this
     morning for LSZ162-263-264.

  Gale Warning until 1 AM EST /midnight CST/ Thursday for LSZ162-

Lake Michigan...


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