Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 231923

Area Forecast Discussion
National Weather Service Marquette MI
323 PM EDT Mon Oct 23 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 323 PM EDT MON OCT 23 2017

Strong storm wqill continue to develop as phasing of systems occurs
over the area. Closed low over se MO and a shortwave over the Red
River valley of the North will phase together tonight with two
closed lows eventually consolidating into one over the eastern U.P
by 18z Tue to 00z Wed. NAM shows some deeper moisture coming in from
the east along with strong 850-500 mb q-vector convergence tonight
through Tue. GFS shows about the same thing as well. One new trend
from the latest model runs is that the sfc low is slighly further
north and also a bit further east and rather than set up in northern
Lake Michigan, it now comes up from Lake Huron and makes it about as
far west as Newberry. Did not make too many changes to the going
forecast. Winds still look strong and kept up the high wind warnings
and the wind advisory. Did expand the wind advisory into Iron and
southern Houghton Counties. Kept up the lake shore flood warnings as
waves will be high as well. Could see up to 3 inches of rain out of
this system as well. Snow should not amount to too much as ground is
still warm and will see very little accumulation in the western high
terrain tonight into Tue morning and up to an inch Tue afternoon.

.LONG TERM...(Tuesday through Sunday)
Issued at 450 AM EDT MON OCT 23 2017

Focus remains on Tue into Tue night with a potentially significant
low pressure system and associated potential threats. Potential
threats include: Damaging winds, lakeshore flooding/beach erosion
from very large Lake Superior waves, and maybe some snow over
portions of the interior W.

Forecast period starts at 12Z Tue. Models are in much better
agreement that a 980-985mb surface low will be somewhere in the
vicinity of eastern Upper Michigan (models vary between northern
Lake Michigan and just north of the SOO). Models show the low
meandering around some but staying in the same general vicinity for
the following 12-18 hours through 00-06Z Wed, then weakening while
shifting to the E. The CMC is a little different in that it starts
around the same area at 12Z, but shifts the low farther south over
the following 12 hours. At this point, there is still uncertainty
given how potent the system will be and how much of an impact the
position/strength of the low will be on winds. Due to this, will not
go with the absolute strongest guidance, but will show a significant
increase in winds/waves from the previous forecast.

Winds: Using a consensus of guidance for the winds, most shoreline
areas and the Keweenaw should see gusts to around 50mph, with 60-
70mph gusts between between Big Bay and Munising or Grand Marais and
also over the tip of the Keweenaw. The exceptions would be over far
western Upper Michigan where shoreline gusts may be a lower and
around and E of Grand Marais where, depending on the track of the
low, winds may be more out of the SE. If the low tracks are
currently shown, strong gusts of possibly 45-55mph would extend
inland over central Upper MI, including as far south as the Escanaba
area. These peak winds would be strongest between 12 and 21Z Tue,
particularly in the 15-18Z time frame. Weaker, but still significant
winds will continue until after 06Z Wed near central and eastern
Lake Superior. The combination of the extent and duration of these
winds would quite likely lead to many trees coming down in the most
impacted areas, likely leading to widespread power outages.

Waves: Waves will increase to 25ft  over central Lake Superior Tue
morning through the afternoon, resulting in lakeshore flooding and
significant beach erosion on the N side of the Keweenaw and
Marquette and Alger Counties. Elsewhere along Lake Superior, peak
waves will range from 14-20ft, leading to lakeshore flooding and
beach erosion.

Snow: With the system now being modeled as more wrapped up, colder
air may allow for some snow accumulations over the interior higher
terrain of the W half Tue evening into Tue night. Currently have the
highest amounts over the higher terrain of Baraga and northern Iron
Counties with 2-4 inches. However, there is a lot of uncertainty in
that since some parameters will be near borderline values for snow
and track/strength will play an important role. Some guidance
suggested higher amounts up to 6 inches, even as far E as our office
in Negaunee Township, but did not feel comfortable going with those
high of values at this time since some models show little to no
snow. Will not issue any headlines for snow at this point given the
uncertainty and borderline amounts in the forecast. Will let the
next couple shifts take a close look.

There is potential for another significant storm system late in the
week, but given model variability/disagreement, did not make any
changes to the forecast during that time frame. Left the blended
initialization untouched for time periods after this upcoming storm.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 119 PM EDT MON OCT 23 2017

VFR conditions should prevail into this evening at KIWD/KCMX/KSAW.
Powerful storm system lifting n thru Lower MI tonight will spread
rain across the area and lead to the development of strong winds
that should gust to 40g50kt or higher at KCMX/KSAW toward the end of
this fcst period. Conditions will fall to MVFR at KCMX and to IFR at
KIWD/KCMX where winds will be more sharply upsloping.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 323 PM EDT MON OCT 23 2017

A powerful fall storm system will lift n across Lower MI tonight
with sfc low pressure ending up over the far eastern U.P. Tue
morning into the afternoon and get as far west as Newberry. High end
storm force winds will develop over central and eastern Lake
Superior late tonight/Tue morning with high end gales over far
western Lake Superior. Hurricane force wind gusts will likely occur
as well late tonight/Tue morning. Winds will diminish w to e Tue
aftn and Tue night. A short period of light winds under 20kt will
occur on Wed as a weak high pressure ridge arrives. Another strong
low pressure system will impact the Upper Great Lakes late this
week, bringing another round of strong gales late Thu/Fri and could
be some storm force gusts with this event.

Upper Michigan...
  Wind Advisory from 7 AM EDT /6 AM CDT/ to 5 PM EDT /4 PM CDT/
     Tuesday for MIZ010>013-084.

  High Wind Warning from 5 AM to 11 PM EDT Tuesday for MIZ001-003.

  Lakeshore Flood Warning from 6 AM to 11 PM EDT Tuesday for

  Wind Advisory from 7 AM EDT /6 AM CDT/ to 11 PM EDT /10 PM CDT/
     Tuesday for MIZ002-009.

  Lakeshore Flood Advisory from 6 AM EDT /5 AM CDT/ to 11 PM EDT
     /10 PM CDT/ Tuesday for MIZ002-009.

  High Wind Warning from 4 AM to 11 PM EDT Tuesday for MIZ005-006.

  Lakeshore Flood Warning from 5 AM Tuesday to 2 AM EDT Wednesday
     for MIZ005-006.

  Lakeshore Flood Advisory from 5 AM to 2 PM EDT Tuesday for

  High Wind Warning from 7 AM to 5 PM EDT Tuesday for MIZ004.

Lake Superior...
  Storm Warning from 2 AM to 2 PM EDT Tuesday for LSZ250-251-267.

  Storm Warning from 2 AM to 11 PM EDT Tuesday for LSZ249-266.

  Storm Warning from 4 AM to 11 PM EDT Tuesday for LSZ243>248-264-

  Storm Warning from 2 AM EDT /1 AM CDT/ to 8 PM EDT /7 PM CDT/
     Tuesday for LSZ241-242-263.

  Gale Warning from midnight EDT /11 PM CDT/ tonight to 2 AM EDT
     /1 AM CDT/ Wednesday for LSZ162-240.

Lake Michigan...
  Gale Warning from 11 PM this evening to 10 AM EDT Wednesday for



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