Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 210451

Area Forecast Discussion
National Weather Service Marquette MI
1151 PM EST Mon Nov 20 2017

Issued at 912 PM EST MON NOV 20 2017

Most notable update to fcst revolves around strong/gusty winds.
Water vapor imagery and RAP analysis show a vigorous shortwave
moving across southern Manitoba into far northern MN. At the sfc,
associated 987mb low pres is over northern Ontario to the sw of
Pickle Lake with trailing cold front cutting across MN. Dry
prefrontal environment noted on regional 00z RAOBS supports dry fcst
until arrival of post frontal low-level moisture and colder air to
kick in lake effect processes very late tonight into Tue morning.

Of more importance is wind. Upstream, a number of sfc obs just ahead
of 6mb/3hr pres rise have indicated peak gusts in excess of 40kt
across ne ND/southern Manitoba/nw MN this evening. Highest gust from
obs was 53kt at Pilot Mound, Manitoba. With positive part of the
pres rise/fall couplet fcst to increase to +8 to 10mb/3hr as it
approaches nw Lake Superior late tonight and then shifts over
western Lake Superior in the morning, the 40+kt gusts currently
being observed upstream are a very good indicator of what will be
seen over the Keweenaw Peninsula late tonight/Tue morning. Rather
vigorous CAA will also support enhanced mixing as air mass moves
over the relatively warm lake waters. Have thus opted to issue wind
advy for Keweenaw/northern Houghton counties for 07z to 18z. Peak
winds up to 50mph, perhaps as high as 55mph, will occur in 09-13z
time frame. Will also include Ontonagon county for 07z-15z, lakeside
locations in particular. Probably won`t see much in the way of
snowfall during the wind advy period as strong winds will displace
orographic enhancement to developing LES farther downstream.

It appears strongest winds will occur in the w or wnw flow in the
wake of first cold front and ahead of secondary trof that drops
across the area on Tue. As a result, eastern counties bordering Lake
Superior may miss out on the more widespread advy level winds.
However, this will be reevaluated thru the night as additional
guidance arrives.

.SHORT TERM...(This evening through Tuesday)
Issued at 302 PM EST MON NOV 20 2017

Main concerns revolve around strong winds that are expected to
develop tonight and continue through Tuesday. A 988hPa surface low
in response to a potent shortwave trough near Winnipeg will track
just north of Lake Superior tonight. An associated trough will swing
SE across the CWA late tonight into Tuesday, ushering in blustery

An initial push of strong southerly winds aloft may mix down to the
surface at times this evening, especially for downslope locations
near Lake Superior. 850hPa temps will then quickly drop behind the
trough across the west overnight and the east on Tuesday. The
combination of cold air advection and an increasing pressure
gradient between thermally enhanced troughing over eastern Lake
Superior and a 1032hPa high building over the Northern Plains will
promote blustery conditions across the CWA, especially along Lake
Superior. NW gusts to 40mph, possibly 45mph, should affect most of
the Lake Superior shore in the NW wind belts. Resultant waves of 12-
15ft along the Lake Superior shore from Shot Point to around Grand
Marais Tuesday afternoon warrants a Lakeshore Flood Advisory for
Alger County due to minor flooding and beach erosion. Additionally,
those traveling to/from downstate should monitor the status of
traffic on the Mackinac Bridge as stronger crosswinds are expected
there overnight through Tuesday.

As for snow, strong winds, modest inversion heights, and fairly dry
air will limit accumulations of expected LES. Snow amounts should
remain below advisory levels for the typical W to NW wind snow belts
across the west overnight into Tuesday, and across the east on
Tuesday. Though winds will be strong, a rather solid/frozen snow
pack in these locations should limit blowing snow to only that which
falls during this event. For that reason, will hold off on any
headlines or Special Weather Statements.

.LONG TERM...(Tuesday night through Monday)
Issued at 302 PM EST MON NOV 20 2017

The mid-upper level pattern will remain fairly progressive into
early next week across the northern CONUS between mean troughing
over the Gulf of Alaska/NE Pacific and troughing over eastern Canada
and the NE CONUS.

Tue night into Wed, nw gradient flow should be gradually weakening
as a shortwave trough pushes e and strong ridging builds in from the
w. 850 mb temps near -15c should equate to a lake-h85 delta-t of
around 20C. Dry air should limit nw flow LES accumulation from 2 to
5 inches Tue night into Wed with the greatest amounts east. A few
spots could reach borderline advisory criteria during the event.
Warming temps and winds becoming w to sw should end any lingering
LES Wed afternoon over the far eastern shoreline.

Another clipper shortwave is progged by models to move from northern
Manitoba into northern Ontario Wed night and Thu bringing another
cold front and quick shot of colder air across the Upper Great Lakes
on Thu. Models differ on how cold the airmass will be with the 12Z
GFS and NAM coming in about 5 degree Celsius colder than either the
12Z Canadian or the 00z ECMWF. Even with the colder GFS/NAM
solutions not expecting much more than 2-3" of nw flow LES
accumulation Thu into Thu evening as again large scale anticyclonic
flow and dry air will limit accumulations.  Backing flow and
moderating temperatures will end any lingering LES Thu night.

Friday into Sunday, both the GFS and ECMWF advertise another strong
shortwave moving across the Upper Great Lakes with a 982 mb sfc low
tracking e through northern Ontario just north of Lake Superior Fri
afternoon and evening. Elevated warm layer in strong warm air
advection ahead of this low pressure system could lead to some mixed
precipitation late Thu night/early Fri in form of light snow/light
fzra before pcpn changes over to mostly rain late Fri morning.
Bigger story with this system will be the wind as ssw wind gusts
ahead of the system could approach advisory criteria over a few of
the eastern counties on Fri. Behind the cold front as winds shift w-
nw, gusts could reach advisory criteria at a few of the more exposed
spots along Lake Superior Fri night into Sat. Looks like a decent
shot of cold air moving in behind the system coincident with the
main shortwave trough and secondary cold front as 850 mb temps drop
near -16c per 12z GFS by late Sat into Sat night. With colder air,
expect light to moderate LES in the NW wind snowbelts. Accumulation
will be likely be limited by dry air beneath lowering subsidence
inversion in large scale anticyclonic flow. LES will taper off from
w to e on Sun as sfc high pres builds in from the w and temps slowly

Model uncertainty increases out to next Mon but the 12z ECMWF and to
a lesser extent the 12z Canadian show another shortwave and
associated sfc low moving through Ontario and glancing northern Lake
Superior. This could bring some light mixed pcpn to the area.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1151 PM EST MON NOV 20 2017

Cold front passing across the area overnight will be followed by the
development of strong w to nw winds, -shsn and MVFR conditions. At
KCMX, winds are likely to gust in excess of 40kt into the morning
hrs. Winds will gust upwards of 35kt at KIWD and 30kt at KSAW. The
gusty winds will also lead to some blsn at KIWD/KCMX. While MVFR
conditions should prevail, will probably see some brief periods of
IFR at KIWD and especially at KCMX where winds will be strongest,
kicking up more blsn. Winds will diminish during the late aftn and
evening. Conditions will improve to VFR at KSAW in the evening.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 302 PM EST MON NOV 20 2017

A strong low pressure system will track eastward just north of Lake
Superior tonight. Southerly winds to 30 knots through early evening
will becoming NW gales of 35 to 40 knots across much of Lake
Superior late tonight through Tuesday. Winds will diminish to under
25 knots while becoming westerly through Wednesday morning, before
backing to SW winds of 20 to 30 knots Wednesday night. Westerly
winds of 20 to 30 knots Thursday will back to the south on Friday.
Another strong low pressure system will then bring the potential for
northwest gales of 35 to 40 knots Friday night into Saturday.

Upper Michigan...
  Wind Advisory until 1 PM EST Tuesday for MIZ001-003.

  Lakeshore Flood Advisory from 11 AM to 9 PM EST Tuesday for

  Wind Advisory until 10 AM EST Tuesday for MIZ002.

Lake Superior...
  Gale Warning from 6 AM to 10 PM EST Tuesday for LSZ248>251-267.

  Gale Warning from 4 AM to 10 PM EST Tuesday for LSZ265-266.

  Gale Warning until 10 PM EST Tuesday for LSZ243>245-264.

  Gale Warning from 4 AM to 4 PM EST Tuesday for LSZ246-247.

  Gale Warning until 5 PM EST /4 PM CST/ Tuesday for LSZ162-

Lake Michigan...
  Gale Warning until 6 AM EST Tuesday for LMZ248-250.



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