Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 130939

Area Forecast Discussion
National Weather Service Marquette MI
439 AM EST Wed Dec 13 2017

.SHORT TERM...(Today and tonight)
Issued at 439 AM EST WED DEC 13 2017

...Slippery Morning and Evening Commutes Expected Across Portions of
Upper Michigan Today...

A clipper system is currently tracking across the Upper Mississippi
Valley as multiple shortwaves evident on water vapor imagery
continue to dig southeast towards the region. 850mb winds have back
to the south-southeast this morning, which allowed lingering lake
effect snow east of Marquette to push offshore this morning. Across
the west, light snow was observed; however, a more robust band of
snow has developed across central Minnesota and northwest
Wisconsin, which will be the main forecast concern for the day.

Today: The main concern is the strong fgen band expected to track
along the Wisconsin/Michigan border through the day today as the
main clipper system tracks across southern Wisconsin this afternoon.
This band is expected to track west to east across western and
central Upper Michigan this morning and will impact the morning
commute. As strong isentropic lift develops along this band of
frontogenesis, expect fairly deep lift to develop and allow for snow
to fall moderate, to even heavy, at times. Forecast soundings show
this deep lift with a fairly deep residence time for hydrometeors
through the DGZ. Therefore, expect this system snow to be rather
efficient. However, with the thermal profile anchored more towards
the -10C isotherm, SLRs should be lower than 20:1, and will make for
a wetter, more sloppy snow. The track of the surface and 850mb low
coupled with 850mb temperatures around -15C, we`re also looking at a
good setup for lake enhanced snow across the south central. This
will lead to localized amounts a bit higher on the west side of the
Bay of Green Bay. The system snow will come to an end across the
west this afternoon, but may linger into the evening hours across
the south central. Across the Keweenaw and eventually north central
Upper Michigan as the 850mb flow comes around to the east and then
northeast later this morning and afternoon, respectively, and
remains between -15 and -18C expect lake enhanced snow to impact
those locations. Across the north central, this lake enhanced snow
will transition over to lake effect by this evening. Did expand the
winter weather advisories and issued an SPS to account for the
impacts expected during the morning and evening commutes.

Tonight: As the clipper system continues to track southeast across
the lower Great Lakes cold air advection will ramp up across the
Upper Great Lakes and allow for lake effect snow to return, if not
already ongoing from this afternoon. As a few weak shortwaves dig
across the region overnight, this will back the 850mb flow and push
the resulting lake effect snow from northeast to northwest snow
belts. With 850mb temperatures progged to remain around -18C over
night, expect lift through the DGZ to be strong enough to support
additional snowfall accumulations, possibly upwards of 3 inches in
some spots.

.LONG TERM...(Thursday through Tuesday)
Issued at 408 AM EST WED DEC 13 2017

Intermittent lake effect snow is expected through much of the
extended forecast with continued colder temperatures. The greatest
impact will likely be early in the extended late Thursday into
Friday evening as moderate to heavy lake effect snow is possible.

Thursday through 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 -16C and -22C, warmest Thursday into Thursday
evening. The colder temperatures will slide in aloft Friday and
Friday night as a reinforcing shot of colder air sinks southward
into the U.P. with another strong shortwave aloft. Initially winds
will be westerly across the U.P. Thursday and Thursday evening;
however, a surface low is expected to develop and intensify over
eastern Lake Superior as this wave digs into the area. This will
effectively shift the winds to the north 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 north to northwest wind favored snowbelts
Friday into Friday evening. Inversion heights are progged to jump to
around 10kft and 15kft as the wave slides overhead. Again, this
would point to a period of heavy lake effect snow late Thursday
night into Friday evening as deep layer moisture and forcing exist
through much of the sounding. Current thinking is that several
inches of lake effect snow may fall from portions of the north-
central 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 are possible
Friday into Friday evening across the eastern half of the U.P.
downwind of Lake Superior.

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 lake effect 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 reinforced over the eastern
CONUS generally allowing for northwest flow aloft as a broad ridge
continues over the western CONUS. This will lead to intermittent
lake effect snow chances through much of this period 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

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1222 AM EST WED DEC 13 2017

MVFR ceilings continue to spread east across the area as snow ahead
of approaching clipper system moves in. IFR visibilities expected
at all three sites as the snow intensifies overnight and early
Wednesday, but conditions to remain IFR at KIWD through the
afternoon and evening while KSAW and KCMX will see MVFR conditions
return late in the forecast as snow ends there.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 408 AM EST WED DEC 13 2017

Winds will remain at or below 25 knots through Thursday night as the
pressure gradient relaxes across Lake Superior. Winds will increase
to 20 to 30 knots late Thursday night through Friday evening as the
next low pressure system develops and strengthens over eastern Lake
Superior. Winds will then remain in the 15 to 25 knots range through
the beginning of the work week.

Upper Michigan...
  Winter Weather Advisory from 11 AM this morning to 1 AM EST
     Thursday for MIZ005.

  Winter Weather Advisory until 7 PM EST /6 PM CST/ this evening
     for MIZ010>013.

Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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