Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 060935

Area Forecast Discussion
National Weather Service Marquette MI
435 AM EST Tue Dec 6 2016

.SHORT TERM...(Today and tonight)
Issued at 435 AM EST TUE DEC 6 2016

Upper air pattern consists of a closed 500 mb low over the northern
plains with a shortwave ridge over the upper Great Lakes this
morning. The closed low moves slowly east and moves an upper trough
into the upper Great Lakes this afternoon and tonight with the low
ending up near Thunder Bay Ontario by 12z Wed. Nam shows some 850-
500 mb q-vector convergence with some deeper moisture moving through
the area today and both exit tonight. Complicated forecast for today
as cold air moves into the area late today. Lake effect does not get
going until tonight and the wind direction does not really help
until late tonight as winds turn more westerly in the Keweenaw. This
was already covered in the forecast. Mixed pcpn this morning will
switch over to all snow late this afternoon with the arrival of the
colder air. Used the prob ice present to depict snow and a narrow
band moves through the cwa today with the cold front. Out ahead of
the cold front, removed snow out of the forecast and went with
drizzle, freezing drizzle and rain showers based on temperatures.
That was the only real big change to the going forecast.

.LONG TERM...(Tuesday night through Monday)
Issued at 330 PM EST MON DEC 5 2016

The main weather impacts, during the extended, will occur Wednesday
through Friday night as significant lake effect snow is expected for
mainly west to northwest wind favored snowbelts. It does look like a
headline will be need for this event within the next day or so.

A sprawling surface low and upper-level 500mb low pressure system
will slowly shift from the northern MN/Ontario border on Tuesday to
western Quebec on Thursday and eastern Quebec on Friday. Initially,
Tuesday night, surface winds will be out of the southwest to west-
southwest as the cold front/surface trough slides through the area
which would begin to give lake effect snow potential over mainly the
Keweenaw Peninsula and possibly over the east; however, the colder
850mb temperatures are expected to be over the west half Tuesday
night. 850mb temperatures over the west are progged to be around -
10C to -12C range while the east is expected to cool at 850mb from
around -8C in the evening to around -10C to -11C overnight on CAA.
Current thinking is that the wind will be more southwesterly through
Tuesday evening which would keep the heavier lake effect snow off to
the west of the Keweenaw, but the more west-southwest wind direction
overnight would help to push the snow bands onshore overnight
Tuesday night, giving only light accumulations (an inch or so) late
Tuesday night.

As the low and trough continues to the east Wednesday through
Friday, winds will be west-southwest Wednesday morning and then
become more westerly throughout the day. This, along with 850mb
temperatures dropping into the -12C to -14C range and additional
shortwaves sliding through the area at the same time, will allow for
the lake effect potential to steadily increase over mainly the
Keweenaw Peninsula; where around 2 to 4 inches of snow are expected
to fall throughout the day. The more westerly winds should keep the
rest of the U.P. in a few snow showers/increased cloud cover
throughout the day. Wednesday night through Thursday the low
continues farther to the east, which will effectively shift the
winds to the northwest across all of the U.P. At the same time,
another shortwave will slide through the U.P. as 850mb temperatures
cool to the -12C to -15C range. This will place the convective cloud
layer and added forcing in the DGZ with inversion heights reaching
to around 10-12kft west and slightly lower over the east. This will
effectively set the stage for heavy lake effect snow for northwest
wind favored snowbelts through Thursday. The lake effect snow will
likely continue for north to northwest wind snowbelt through Friday
night before winds begin to shift to the south and southwest by
Saturday afternoon as shown by both the EC and GFS. Either way, west
to northwest wind favored snow belts will end up with several inches
of snow by Friday afternoon. Early estimates continue to suggest a
foot or more of lake effect snow through Thursday with several more
inches possible in northwest snow belts Thursday night into Friday.
North to northwest wind favored locations will also see moderate
snowfall accumulations from late Thursday afternoon through Friday

Looking farther out, it looks like much colder air will begin to
slide south out of Canada toward the middle of next week. Again, the
trend looks colder than normal for that time period, but the exact
details will need to be ironed out as that time approaches.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1201 AM EST TUE DEC 6 2016

Ahead of an approaching disturbance, regional radars currently show
some returns across the area. With this pcpn aloft fighting a layer
of drier air below, any pcpn, -ra/-sn, that occurs should have
little impact at KIWD/KCMX/KSAW. Otherwise, expect VFR conditions to
continue at KIWD/KCMX overnight. At KSAW, developing upslope flow
off Lake MI is likely to lead to IFR cigs overnight. Not out of the
question for LIFR during the early morning hrs and perhaps a bit of
-FZDZ. Expect conditions to fall to MVFR at KIWD/KCMX this morning
while KSAW improves to MVFR. There may be a period of -sn today at
all terminals as well.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 435 AM EST TUE DEC 6 2016

Period of active weather will continue this forecast period.
Gradient is expected to tighten up this morning with a period of
gales east of the Keweenaw over Lake Superior into early afternoon.
Gales in the far western portion of the lake this afternoon into
Wed. Another brief gradient increase will occur Wed, before winds
shift from southwest/west to northwest coupled with much colder air
flowing across the lake Thur into Fri. This coupled with winds
mainly between 25-30kt and occasional gales to 35 kt will allow
waves to easily build later in the week.

Upper Michigan...
  Lake Effect Snow Advisory from 7 AM Wednesday to 7 PM EST Friday
     for MIZ001-003.

  Lake Effect Snow Watch from late Wednesday night through Friday
     evening for MIZ002-004-005-009.

  Lake Effect Snow Advisory from 1 AM Thursday to 7 PM EST Friday
     for MIZ084.

  Lake Effect Snow Advisory from 1 AM Thursday to 7 AM EST
     Saturday for MIZ006.

Lake Superior...
  Gale Warning until 1 PM EST this afternoon for LSZ264>267.

  Gale Warning from 4 PM EST /3 PM CST/ this afternoon to 10 AM
     EST /9 AM CST/ Wednesday for LSZ162.

  Gale Warning from 4 PM this afternoon to 7 PM EST Wednesday for

Lake Michigan...


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