Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 102033
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
333 PM EST Sun Dec 10 2017

.SHORT TERM...(Today and tonight)
Issued at 444 AM EST SUN DEC 10 2017

Main concern in the short-term will be increased lake effect
snowfall potential today. Advisories continue into early this
afternoon for most locations along Lake Superior.

Today: A trough sagging south across Lake Superior this morning,
will be the initial focus for lake effect/enhanced snowfall across
the Keweenaw and eastern Lake Superior early this morning. The
trough will into the rest of the central and eastern U.P. by
daybreak. This will allow snow coverage and intensity to increase
across north central and eastern Upper Michigan as the trough
passes. Then, winds are expected to shift to the north and northwest
into the early afternoon hours. This, along with a quick moving
shortwave moving through, will allow lake effect snow to continue on
the back side of the trough as 850mb temperatures drop to around
-18C to -20C across the area. The Keweenaw will see the better
chances of snow early in the day as the trough sinks southward;
however, the northerly wind direction is less favorable for heavier
lake effect snow in that area and inversion heights drop to around
3kft by late morning. This should allow for only a few additional
inches of snowfall through mid to late morning, when the advisory
expires. Over the north-central and eastern U.P., the increase fetch
across Lake Superior, along with the aforementioned colder
temperatures aloft, will allow for at least moderate lake effect
snow even after the initial trough slides through the area early
this morning. Inversion heights are progged to be around 5kft to
7kft this morning before coming down to around 3kft by early to mid
afternoon when the advisory is set to expire in those locations.
Current thinking is that a widespread 3 to 6 inches of snow could
fall from near Big Bay to Harvey and point east near Lake Superior.

Tonight: A weak ridge will slide across the Upper Great Lakes this
evening, which will allow the lake effect potential to steadily
diminish across all of the U.P. This will especially be true by late
evening as the next low pressure system begins to approach from the
west, effectively shifting winds to the south across the area. This
doesn`t necessarily mean that the snow will completely end; however,
as another shortwave and associated surface low brush past the
western U.P., the chances for light system snow will increase late
tonight for the far western U.P. and along the WI border. At this
point, this looks to be just a quick shot at some light snow for
those areas with an inch or two accumulation expected. Most of the
U.P., away from the WI border will see an inch or less.

.LONG TERM...(Monday night through Sunday)
Issued at 332 PM EST SUN DEC 10 2017

The dominant pattern of an upstream amplified ridge will persist,
and will maintain the downstream trough over the Great Lakes region
through the bulk of the extended periods. Closer to Thur/Fri,
ensembles do begin to indicate the ridge beginning to relax
marginally; however, guidance continues the theme of quick clippers
skirting the Upper Midwest/Great Lakes.

The more concerning feature in the medium term, Mon ngt-Tue ngt,
will be on a departing clipper that will bring strong winds to the
Upper Peninsula. In addition to the tight pressure gradient poised
to develop, it also appears favorable for good LES bands setting up.
With winds turning northeasterly then northerly, the most favored
areas will likely be Northeast Marquette County stretching east
through Alger County. SLRs have continued to be progged around 25:1
to possibly 30:1, with QPF totals between 0.4 to 0.6", resulting in
snowfall in excess of 8" to possibly much higher than a foot in
places by late Tue ngt. Further away from Lake Superior and snowfall
totals diminish significantly, to possibly sub-advisory conditions.
But the wildcard could be the gusty winds causing blowing-drifting
conditions and reduced visbilities in places from fresh snowfall in
prior days. Much colder temps will also accompany the back edge of
the departing shortwave, as a potent thermal trough dives into the
Great Lakes region. Temps will struggle to warm beyond the single
digits...likely warming into the low/mid teens by late Tue aftn. But
given the gusty winds, wind chill values will linger around zero to
a few degree below zero.

Tue ngt-Sat: Troughing will finally begin to lift/pivot east,
allowing mid-lvl heights to rise and create more of a
diffluent/dry flow aloft. This should diminish the coverage of LES
and any organized snow bands across the U.P. for a few periods;
however, flow will eventually turn northwesterly and help to re-
energize some snow showers later in the week. Guidance is keeping
up with a semi- active setup, with another clipper system arriving
Thur. The only wrinkle with the Wed ngt/Thur system could be a
period of strong parcel ascent along front edge, resulting in
faster moistening of the profile and development of snow showers
earlier. This could translate into yet another period of
moderate/heavy snow. Temps will continue to be sub-seasonal with
highs in the upper teens to perhaps mid 20s by late next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 120 PM EST SUN DEC 10 2017

Typical lake effect scenario playing out right now, but that will
gradually diminish through this evening. Synoptic snow will move in
late tonight into Mon morning, mainly impacting KIWD and possibly
KSAW. Behind that low pressure system, more lake effect kicks in
late Mon into mid-week.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 444 AM EST SUN DEC 10 2017

Northeasterly winds will gust to 20 to 30 knots this morning with
freezing spray possible, especially across the eastern half of Lake
Superior. Tonight, winds will weaken to below 20 knots but then
increase Monday afternoon into Monday night with gale force gusts to
40 knots and heavy freezing spray possible. A gale watch has been
posted for Monday afternoon into Monday night for central and
eastern portions of Lake Superior. Winds will then weaken to 20 to
30 knots on Tuesday and below 20 knots on Wednesday. The pressure
gradient will increase across Lake Superior Wednesday night into
Thursday, allowing winds to once again increase to 20 to 30 knots.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Storm Watch from Monday afternoon through late Tuesday
     night for MIZ005-006.

Lake Superior...
  Gale Warning from 7 PM Monday to 7 AM EST Tuesday for LSZ248>251-
     265>267.

  Gale Warning from 4 PM EST /3 PM CST/ Monday to 1 AM EST
     /midnight CST/ Tuesday for LSZ162-240>242-263.

  Gale Warning from 4 PM Monday to 7 AM EST Tuesday for LSZ243>245-
     264.

Lake Michigan...
  Gale Warning from 7 PM Monday to 7 AM EST Tuesday for LMZ221-248-
     250.

&&

$$

SHORT TERM...KEC
LONG TERM...Beachler
AVIATION...Titus
MARINE...KEC



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