Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 152224

Area Forecast Discussion
National Weather Service Marquette MI
524 PM EST Fri Dec 15 2017

.SHORT TERM...(This evening through Saturday)
Issued at 251 PM EST FRI DEC 15 2017

...Isolated bands of moderate to heavy lake effect snow into

Sfc low over eastern Lk Superior deepened more than forecast 24 hour
ago, now down to 1003mb near Sault Ste Marie. Trough extending west
of the low has a subtle wind shift along it and has seemed to flare
up snow showers over interior sections, but otherwise the trough is
hard to pick out. Heaviest lake effect today has stayed along the
shore of Alger county though are starting to see the snow expand
farther inland with even ERY briefly down to 1/4 mile in the last
hour. As the trough continues to drop across Upper Michigan late
this aftn, expect northwest flow lake effect to become more
widespread along Lk Superior. Strongest convergence will continue to
be focused over Alger county. Also looks like at least a weak
shortwave moving across through early this evening will further
enhance the snow over the eastern forecast area. Earlier update
already put Alger into a winter storm warning for heavy lake effect
snow. The snow over eastern Alger county will slowly shift to the
western part of the county late this evening as even though sfc
winds stay mainly west to northwest, H950-H925 winds gradually veer
north to northeast. In general followed NAM/GEM idea for winds
through tonight, but did lean on higher res guidance of WRF-ARW/NMM
for higher qpf/snow amounts. Other issue with this stronger band of
heavy snow is westward progression into eastern Marquette county.
Expect the heaviest snow tonight to stay mainly along the
Marquette/Alger county line as west-northwest sfc winds will persist
due to temps inland falling to near zero/increasing land breeze.
However, late tonight into Saturday morning, sfc winds becoming more
north to northeast as high pressure builds to north of Lk Superior
should push the heavier snow onshore vcnty of Harvey and Marquette.
Since sfc-h925 winds are light 10-15 kts, heavier snow may stay
pinned along the shore instead of setting up farther west over the
higher terrain as some of the high res guidance shows. That will be
something to watch though. Snow will be very fluffy with SLRs late
tonight into Sat likely over 30:1 maybe even toward 40:1. Snow could
add up very quickly because of these higher SLRs.

Over the west, expect mainly multiband lake effect to reorganize
overnight as winds become more east to southeast due to the high
building north of Lk Superior and as sfc low slides from northern
plains to Upper Mississippi River valley. Area of stronger
convergence should briefly form late evening into the overnight for
northern Gogebic into northwest Ontonagon vcnty of Porcupine Mts.
Increased snow totals into the evening those areas. Late tonight
that snow should move offshore as winds become southeast enough.
Another issue late tonight into Saturday is over northern Baraga
county as northeast winds may at least briefly focus heavier band of
snow vcnty of Baraga and L`Anse. Effective lake equilibrium levels
are still over 6kft AGL and temps at inversion top near -20c give
very high over-water instability. All the convective layer will be
within the DGZ so again looking at fluffy snow. Hazard over Baraga
should end late tonight as winds become more easterly there.

On into Sat, the main focus other than eastern Marquette county will
shift to the Keweenaw. Similar setup to what occurs late tonight
with similar inversion heights and availability of the DGZ and a
longer fetch support several inches of fluffy snow on the Keweenaw
for Saturday. Extended the winter weather advisory through late Sat
aftn to account for this potential. Farther inland on Sat, looks
like the low pressure wave and an associated swath of light snow
will stay just far enough south to keep most areas dry. East
drainage winds will keep far east coldest with max temps only lower
teens. Elsewhere expect temps to reach upper teens to near 20F.

.LONG TERM...(Saturday night through Friday)
Issued at 259 PM EST FRI DEC 15 2017

Saturday night through Monday: A relatively benign period of weather
is expected during this time. Weak WAA may bring result in very
light snow or possibly freezing drizzle across mainly the southeast
half of the Upper MI Sunday afternoon and evening. Otherwise,
temperatures should be slightly above normal during this period.

Monday night through Wednesday afternoon: The somewhat disjointed
phasing of two mid-level troughs will be ongoing across the Upper MS
Valley Monday evening. Moderate snow showers will accompany this
trough across the CWA late Monday evening into early Tuesday
morning, especially across the north half. Strong NW winds behind
the trough will be enhanced by a modest isallobaric wind. The
combination of gusty W to NW winds to 40mph and lake effect snow
will likely cause intermittent white out conditions across the
Keweenaw Peninsula through much of the day Tuesday, and along Lake
Superior east of Marquette Tuesday afternoon and evening. While even
stronger winds are not out of the question, the complicated phasing
of the troughs and that fact that this event is still four days out
supports a more modest forecast at this time. Either way, a period
of moderate lake effect snow for the W to NW wind snow belts is
expected Tuesday afternoon through Wednesday afternoon.

Wednesday night through Saturday: A potent mid-level trough moving
over the NW CONUS Tuesday night will become stretched across the
central CONUS by Thursday afternoon. There is considerable model
disagreement on the evolution of the northern portion of this trough
as it crosses the region late Wednesday night into Friday. The
deterministic GFS and a handful of GEFS members are indicating a
swath of moderate WAA snow across the CWA late Wednesday night
through Thursday afternoon. All other solutions favor a stronger
southern flank of the trough across the Lower MS Valley, with some
northern energy bringing a couple rounds of light snow Thursday
through Friday. However, it is far too early to take much stock in
any of these solutions given the expected complex evolution of the
western trough.

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 523 PM EST FRI DEC 15 2017

Lake effect snow showers with IFR-MVFR conditions will continue
through tonight at IWD and through most of Sat at CMX. Could see
occasional LIFR vsby on Sat at CMX if a stronger easterly wind band
of lake effect snow ends up impacting the terminal. At SAW expect
mostly VFR conditions through tonight but as winds turn northerly
late tonight into Sat morning, could see IFR to MVFR conditions
briefly develop before improving by midday Sat.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 251 PM EST FRI DEC 15 2017

Winds will stay generally below 20 knots through the weekend except
for a few northwesterly gusts to 30 knots this afternoon over
eastern sections. Southwesterly winds will increase late Monday to
20 to 30 knots before veering to northwesterly gales to 35-45 knots
late Mon night through Tue night. With increasing wave heights,
freezing spray is possible Tuesday night into Wednesday.

Upper Michigan...
  Winter Storm Warning until 1 PM EST Saturday for MIZ006.

  Winter Weather Advisory until midnight EST /11 PM CST/ tonight
     for MIZ002-007-009-085.

  Winter Weather Advisory until 1 PM EST Saturday for MIZ004-084.

  Winter Weather Advisory from midnight tonight to 1 PM EST
     Saturday for MIZ005.

  Winter Weather Advisory until 5 PM EST Saturday for MIZ001-003.

Lake Superior...
Lake Michigan...


LONG TERM...Kluber
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