Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 140935

Area Forecast Discussion
National Weather Service Marquette MI
435 AM EST Thu Dec 14 2017

.SHORT TERM...(Today and tonight)
Issued at 435 AM EST THU DEC 14 2017

Early this morning, lake effect snow continued across the north-
northwest wind snow belts, with multiple narrow bands of moderate
snow impacting eastern Marquette and much of Alger counties. A
number of shortwaves were evident across central Canada on water
vapor imagery tracking south-southeast towards the Upper Great

Through the morning hours, the lake effect snow will continue to
shift from the north-northwest to west wind snow belts. At times the
lake effect across the east may fall moderately, but is expected to
remain progressive so opted to hold off an issuing a winter weather
advisory for this morning. Did however issue an SPS highlighting
additional accumulating snow this morning and possible slick
conditions due to continued snow covered roads. Out west, the lake
effect snow is expected to remain light as weak surface ridging
attempts to work in from the Arrowhead of Minnesota.

Later this afternoon as a weak shortwave digs south across the lake,
this will reinforce surface troughing oriented west to east across
the northern half of Upper Michigan and southern Lake Superior. The
increased convergence along this surface trough out west will allow
the ongoing lake effect to intensity this evening; therefore, opted
to start the new winter weather advisory this evening across the far
west and the move up the spine of the Keweenaw Peninsula overnight.
Across the east, the lingering lake effect snow as mentioned above
will remain progressive but should focus more across eastern Alger
and northern Luce counties. Across the central, we could see some
light snow/flurries, with the exception of the south central where
they should remain mostly dry.

Tonight: Across the west, ongoing lake effect will further intensify
and transition from the west to northwest wind snow belts as a
strong, potent shortwave digs across the region ushering another
bout of cold air advection across the region. With the arrival of
the shortwave and additional cold air, forecast soundings show
inversion heights across the west rising to around 10-12k ft, strong
lift through the DGZ, and ample lake-induced CAPE. Also, with the
lingering surface trough providing additional lift across the west,
expect snow to fall moderate to heavy at times. It is possible that
a few counties across the far west may need to be upgraded to a

Across the central, as the above mentioned shortwave digs across the
region, widespread snow will be possible. However, do not expect
much more than a dusting to an inch, especially across the south
central. Across the north central, things get a bit tricky as it
will depend on where the surface trough is oriented, as it could
lead to localized lift and increased snowfall amounts.

Across the east, how things play out will depend on whether or not
the west to east oriented snow band along the trough axis makes it
onshore. Eventually the lake effect snow is expected to push
onshore, but there is uncertainty in the timing. Therefore, did opt
to hold off on issuing any headlines during this time period, but
certainly at least advisories will be needed as that band pushes
onshore. Right now models are consistent with the surface trough
lingering across southeast portions of Lake Superior with strong
convergence and resulting lift through 1000-850mb hugging the
shoreline of Alger and Luce counties; however, they do push the QPF
onshore rather quickly. Right now, think there should be a decent
land breeze overnight, due to the land/lake temperature difference,
that will lead to enhanced convergence along the surface trough, but
should help keep the band offshore until the trough starts to move
onshore towards Friday morning. As mentioned above, there will
likely need to be advisories, but given the deepening convective
layer and ample lift through the DGZ if stronger bands have a longer
residence times, a winter storm warning may be needed.

.LONG TERM...(Friday through Wednesday)
Issued at 407 AM EST THU DEC 14 2017

Intermittent lake effect snow is expected through much of the
extended forecast with continued colder temperatures; however, there
will be some slight moderation in temps this weekend before colder
air moves in again. The greatest impact will likely be early in the
extended Friday into Friday evening as moderate to heavy lake effect
snow is possible for northwest wind snow belts.

Friday and Friday night: The deep troughing over the eastern CONUS
is expected to linger through this time period allowing below normal
temperatures to remain in place. 850mb temperatures are progged to
be between -18C and -22C Friday through this time period. Colder
temperatures will slide in at the surface as a reinforcing shot of
colder air sinks southward into the U.P. with another potent
shortwave aloft. A surface low is expected to develop and intensify
over eastern Lake Superior as this wave digs into the area and
heating from the lake helps to deepen the low. This will effectively
allow winds to become north-northwest to northwest across much of
the area, especially over the eastern half of the U.P. This would
allow for favorable conditions for a period of moderate to heavy
lake effect snow for the aforementioned snowbelts Friday into Friday
evening. Inversion heights are progged to jump to around 10kft to
13kft as the wave slides overhead. Again, this would point to a
period of heavy lake effect snow during this time period as deep
layer moisture and forcing exist through much of the sounding and
most notably the DGZ. Current thinking is that several inches of
lake effect snow will fall from portions of the northwest U.P. and
especially through the eastern U.P. along Lake Superior. Models are
fairly similar in pegging those areas for the heavier snow; however,
a slight change in wind direction will shift the favored snow bands.
Stay tuned for updates for this time period, but it does appear that
headline worthy snowfall totals can be expected Friday into Friday
evening across the eastern half of the U.P. downwind of Lake
Superior. Issued a winter weather advisory for the western U.P.
through Friday afternoon; however, as the trough shifts east, the
snow should begin to taper off by late Friday afternoon over the
west. The eastern U.P. will likely need at least an advisory
through Friday morning through Friday night, while the north-
central U.P. may also need an advisory through Friday afternoon
into possibly Saturday morning as winds become more north to

Saturday into Sunday: A weak low pressure system is expected to
slide to the south of the U.P. as yet another upper-level
disturbance slides across the Upper Great Lakes.  This will provide
just enough moisture and lift to provide very light snow or possibly
flurries across the U.P. 850mb temperatures moderate significantly
with much of the area seeing 850mb temps in the -6C to
-8C range.  This will minimize any lake enhancement for this time
period. Surface temperatures will warm as well with most locations
seeing highs in the mid to upper 20s by Sunday.

Rest of the extended: Broad troughing is expected to be reinforced
over the eastern CONUS by Wednesday allowing for northwest flow
aloft as a broad ridge builds over the western CONUS. This will lead
to intermittent lake effect snow chances picking up once again
Wednesday through the rest of the extended with the favored bands
depending largely on the low to mid level flow. Models differ on
timing of the better shortwave enhancements during this time period,
which is typical for the end of the extended forecast; therefore,
will stick with a consensus of the models with the intermittent lake
effect snow chances, mainly downwind of Lake Superior. There is a
hint of a stronger low pressure system pushing into the area next
Thursday into Friday; however, models are having trouble with time
and placement. Again, will stick with consensus for this time period
with the introduction of pops next Thursday.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1138 PM EST WED DEC 13 2017

Lake effect snow showers will continue at all terminals at times
with MVFR ceilings and variable reduced visibilities. Lake effect
snow showers will end by afternoon at KSAW.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 435 AM EST THU DEC 14 2017

Winds will between 10 and 20 knots are expected today, but will
increase to around 20 to 25 knots tonight through Friday as low
pressure develops and strengthens over eastern portions of the lake.
Friday night through the weekend, winds look to remain in the 15 to
25 knot range. Early next week, winds will ramp up to between 20 t0
30 knots. Gales may be possible.

Upper Michigan...
  Winter Weather Advisory from 10 PM this evening to 4 PM EST
     Friday for MIZ001-003-004-084.

  Winter Weather Advisory from 5 PM EST /4 PM CST/ this afternoon
     to 4 PM EST /3 PM CST/ Friday for MIZ002-009.

Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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