Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 240938

Area Forecast Discussion
National Weather Service Marquette MI
538 AM EDT Tue Oct 24 2017

.SHORT TERM...(Today and tonight)
Issued at 537 AM EDT TUE OCT 24 2017

Water vapor imagery and RAP analysis show that the vigorous
shortwave that was over the Lower Mississippi Valley 24hrs ago has
lifted into northern Lwr MI in response to a strong shortwave
digging into the Ohio Valley. At the sfc, rapidly deepening sfc low
is near Mackinac Island, and the pres is down to 29.0 inches. As
expected, large area of rain, mdt to hvy at times, associated with
the system is currently spreading w across the fcst area. Winds are
quickly ramping up. Gusts of 40-45mph have been reported from
Munsing to Newberry so far.

Going fcst is on track with what has been forecast for the last
24hrs. Sfc low is nearly finished with its deepening phase and
should meander into far eastern Upper MI this morning before
weakening trend begins this aftn, followed by an ene movement
tonight. Low-level wind fields will peak this morning with a
corridor of 65-70kt 850mb winds curving across eastern Lake Superior
into Marquette/Alger and Delta Counties. As a result, expect the
strongest sustained winds and gusts, aimed across s central Lake
Superior into the area btwn Marquette and Munising. Damaging wind
gusts of 65 to perhaps 70mph should occur at times for at least a
few hrs this morning. Winds only tail off very slightly farther w
into the Keweenaw, so still expect gusts to 60+mph in that area.
Overall, ongoing high wind warning headlines appear to be good
shape. Considered adding Delta to warning given the corridor of
strongest winds aloft extending over that area, but lack of caa
should limit efficient mixing and the potential of gusting
frequently to 58mph or more. Will be something to monitor. Main
headline change was to add Schoolcraft and Luce counties to wind
advy as strengthening band of winds translates e across that area
over the next few hrs. Expect gusts of 45-55mph. As the low drifts
into far eastern Upper MI today, the eastern edge of the strong wind
band will likely shift w of Luce County and perhaps Schoolcraft
County before the stronger winds shift back e later in the day. No
changes to lakeshore flooding along Lake Superior.
Significant/damaging beach erosion and beach flooding is expected
around the n side of the Keweenaw and along the beaches of
Marquette/Alger Counties as waves build upwards of 25ft. Lake
Superior is currently about 10 inches above the long term avg Oct
water level, which will exacerbate the beach erosion/flooding.

Other concern is ptype. Synoptic pcpn shield will continue to spread
w over the next few hrs and will probably make it to far western
Upper MI. Although the intensity of the synoptic pcpn will diminish
as it spreads w, cooler air mass with 850mb temps falling to 0 to
-4C over that area will lead to lake enhancement, further aided by
upsloping. Utilizing wetbulb zero heights from the NAM/GFS/RAP
suggests snow will begin to mix with the rain over the higher
terrain of the w by late morning and w of a Marquette to Iron Mtn
line during the aftn. Highest terrain should change over to all snow
this aftn. Took a conservative approach to the changeover and
possible snow accumulations today with only an inch or two over the
high terrain of far western Marquette County/Baraga County into
Iron/Gogebic counties. That said, not completely out of the question
that we could have a surprise with significant hvy/wet snow
accumulations over the high terrain of the nw half of Upper MI,
particularly around the Huron Mtns.

With influx of drier air, pcpn will diminish/end over the w tonight
with lake effect keeping pcpn streaming off Lake Superior over the n
central/ne fcst area. Pcpn will continue to mix with or change to
snow from w to e. May see another inch or so of snow over the high
terrain of the interior w half. Another disturbance dropping se thru
the Upper Mississippi Valley into the Great Lakes trof could spread
some -shsn into far western Upper MI late tonight.

.LONG TERM...(Wednesday through Monday)
Issued at 508 AM EDT TUE OCT 24 2017

Mainly spent time supporting short term operations with the upcoming
system. No changes in overall thinking from the previous shift with
a clipper that may impact the area late in the week.

A clipper system will pivot across the Upper MS Valley into the
Upper Great Lakes Thursday afternoon through Friday. While model
guidance differs on the track across Upper Michigan, the air mass
will be cold enough to support several inches of accumulating snow
for at least the interior west Thursday night. A slight shift north
or south in the low pressure track will result in considerable
differences in potential snow, so will continue to follow a middle-
ground approach to the forecast this far out.

Saturday through Monday, a seasonably cold air mass will support a
period of lake effect precipitation, mainly in the form of snow, for
the north to northwest wind snow belts.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 133 AM EDT TUE OCT 24 2017

A powerful, deepening storm system lifting nnw toward the Straits
by early this morning will spread rain across the area and lead
to the development of strong nrly winds that should gust to
40-45kt or higher at KCMX/KSAW from this morning into the
afternoon. Conditions will fall to MVFR at KCMX and KIWD and to
IFR at KSAW where winds will be more sharply upsloping along with
the heavier rain. Some snow will also mix with the rain by this
afternoon at KIWD and this evening at KCMX/KSAW. Otherwise, expect
imrprovement by late afternoon to MVFR at KSAW with slightly
diminishing winds. Drier air moving into the west this evening
will also allow cigs to lift to VFR at KIWD.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 537 AM EDT TUE OCT 24 2017

A powerful fall storm system will meander over far eastern Upper MI
today. Storm force winds dominate much of Lake Superior, except the
w. Highest winds will be over the central where some hurricane force
wind gusts to 65 to potentially 70kt will occur. Winds will diminish
a bit over far eastern Lake Superior this aftn, closer to the low
pres. Winds will diminish w to e tonight/Wed morning. Should see a
short period of light winds under 15kt over much of the lake at some
point later Wed into Wed evening as high pres ridge briefly moves
over the area. Winds will then ramp up as another strong low
pressure system approaches, arriving over the Upper Great Lakes Thu
night/Fri. Gales will likely occur late Thu/Fri.

Upper Michigan...
  Wind Advisory until 8 PM EDT /7 PM CDT/ this evening for

  Wind Advisory until 8 PM EDT this evening for MIZ014-085.

  High Wind Warning until 11 PM EDT this evening for MIZ001-003-

  Lakeshore Flood Warning until 11 PM EDT this evening for MIZ001-

  Wind Advisory until 11 PM EDT /10 PM CDT/ this evening for

  Lakeshore Flood Advisory until 11 PM EDT /10 PM CDT/ this
     evening for MIZ002-009.

  Lakeshore Flood Warning until 2 AM EDT Wednesday for MIZ005-006.

  Wind Advisory until 3 AM EDT Wednesday for MIZ007.

  Lakeshore Flood Advisory until 2 PM EDT this afternoon for

  High Wind Warning until 5 PM EDT this afternoon for MIZ004.

Lake Superior...
  Storm Warning until 11 PM EDT this evening for LSZ243>251-

  Storm Warning until 8 PM EDT /7 PM CDT/ this evening for LSZ241-

  Gale Warning until 2 AM EDT /1 AM CDT/ Wednesday for LSZ162-240.

Lake Michigan...
  Gale Warning until 10 AM EDT Wednesday for LMZ221-248-250.



SHORT TERM...Rolfson
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