Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 151725 AAA

Area Forecast Discussion...UPDATED
National Weather Service Marquette MI
1225 PM EST Fri Dec 15 2017

Issued at 1223 PM EST FRI DEC 15 2017

Have tweaked pops/qpf/snow amounts and associated hazards into Sat.
Main change was to upgrade winter weather advisory for Alger county
to a winter storm warning for heavy lake effect snow this aftn
through tonight. Leaned on blend of higher res guiance which has
been doing well thus far today to come up with qpf/snow for tonight.
Snow tonight will be especially focused in a dominant band over
western portions of Alger county with sfc winds west to northwest
and winds at 925mb gradually veering more north to northeast. Strong
convergence and high SLRs seen with snow since ydy of at least 25:1.
Other issue with this 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 but late tonight
into Saturday morning, sfc winds becoming more north to northeast as
high builds to north of Lk Superior should push the heavier snow
onshore vcnty of Harvey and Marquette. Since sfc-h925 winds are
light think the heavier snow will 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 the higher SLRs.

Other issue late tonight into Saturday was 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. Then 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.

.SHORT TERM...(Today and tonight)
Issued at 435 AM EST FRI DEC 15 2017

A shortwave over the area is driving some light snow across the
area, with lake effect in the NW snowbelts of the western U.P. and a
band of heavy lake effect N of the Superior shorelines of eastern
Upper MI. Behind the shortwave, wind fields will allow LES to move
onshore in the NW wind snowbelts of the E this morning. Little
change in thinking from the previous shift, so no headline changes
were needed. Lake effect diminishes to a degree tonight, lingering
strongest longest into eastern Marquette and far western Alger
County through tonight. From 12Z today to 12Z Sat, additional
accumulations are expected to be 3-5" in the snowbelts of the
western half, 5-8", possibly up to 11", in Alger and northern
Schoolcraft, and 2-5" in Luce County.

.LONG TERM...(Saturday through Thursday)
Issued at 350 AM EST FRI DEC 15 2017

Beginning Saturday: With sfc high pressure sliding north and east of
Lake Superior and 850 mb temps in the -16C to -20C range, expect
some lingering light lake effect snow mainly in e to ne flow areas.
Very light snow of a up to a few tenths of an inch forced by WAA may
also occur along the Wi border counties, but overall impacts should
be minimal.

Sunday and Monday: Mainly zonal flow aloft along with weak surface
ridging and increasing 850 mb temps will allow for mostly dry
conditions and moderating temps during this time.

Tuesday through Wednesday: A shortwave trough moving in Mon night
will usher in another shot of colder air into the region generating
more LES for the W to NW wind snow belts Tuesday into Wednesday.
Gusty west to northwest winds, especially across the Keweenaw and
north central shoreline areas, will be possible Tuesday into Tuesday
night aided by an isallobaric wind component crossing the CWA behind
the trough. Mixed layer off the GFS forecast soundings would suggest
several locations reaching advisory criteria wind gusts of 45 mph
or greater.

Wed night into Friday: Model uncertainty increases for later in the
week regarding evolution of a low pres system developing over the
Plains and moving into the Great Lakes region. The 00z ECMWF
solution is not as deep and farther south than its previous run and
shows the low taking a similar track as the 00Z GFS and GEFS through
central Lower Mi and across Lake Huron Thu night into Fri morning.
Following a blend of the 00z GFS and ECMWF solutions...WAA snow
ahead of this system would spread into Upper Mi late Wed into Wed
night and continue into Thu with the potential for significant lake
enhanced snow over the northeast snow belts Thu afternoon into
Friday morning.  Model trends on this developing storm system and
its potential impact on holiday travel will need to be monitored
heading into next week.

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 649 AM EST FRI DEC 15 2017

Lake effect snow showers will continue at KCMX and KIWD. KSAW will
have light snow into this morning.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 435 AM EST FRI DEC 15 2017

Winds will stay generally below 20 knots through the weekend except
for a few northwesterly gusts to 30 knots today. Southwesterly winds
will increase late Monday to 20 to 30 knots before veering to
northwesterly gales to 35-45 knots late Mon night into Wed morning.
With increasing wave heights, freezing spray is possible late
Tuesday night and 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...


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