Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 171931

Area Forecast Discussion
National Weather Service Marquette MI
231 PM EST Fri Jan 17 2020

.SHORT TERM...(Today through Saturday)
Issued at 412 AM EST FRI JAN 17 2020

Well...looking at the regional temperatures, it becomes pretty clear
which areas have seen lake-effect clouds remain overhead and who has
not. Currently around -20F in Gogebic County and close to -15F in
Iron County. Upper-level winds have taken a little longer to back
westerly this morning as remnant lake-effect clouds over much of
Upper Michigan, except counties along the WI border. Rapid refresh
models this morning suggest 850 winds will continue to back more
southwesterly through the rest of the morning and allow additional
clearing/cooling. Expecting temps to fall to near 0(or much colder
along the WI border where clear skies have been the rule) somewhere
along and south of a line from Ontonagon to Gladstone.

Today into tonight, Upper Michigan will be caught between an upper-
level ridge and trough as the final shortwave in this week`s parade
is progged to lift from the Central Plains through Lower Michigan by
Saturday afternoon. Leeside cyclogenesis will be the result tonight
as the wave pivots to a negative tilt lifting into Upper Michigan.
Ahead of this wave and developing low pressure system, a nose of
higher theta-e, along a 50kt LLJ, will track into Upper Michigan
between the exiting ridge and approaching trough. Models suggest
this nose of theta-e to coincide nicely with the increase of PoPs as
WAA and isentropic ascent follow shortly behind. As the wave pivots
and continues to lift to the northeast, decent pressure falls move
across south and east Upper Michigan to the tune of 1-2mb/hr from 6
to 15Z Saturday. In terms of purely the system snow, expecting this
time frame to bring the worst impacts for most of Upper Michigan.
High-res models have been consistently pegging additional lake-
enhancement across the Keweenaw and immediately along Lake Michigan
shoreline under SE flow through 12Z Saturday. As the open wave
pivots to the east across Lake Michigan tomorrow afternoon, winds
slowly trend to the northwest sometime around 00Z Sunday. This looks
to be the next chance for a blast of significant snowfall across the
NW wind LES belts. Models suggests a pretty potent convergence band
to develop as NW winds across w Lk Superior clash with still NE
winds across C Lk Superior and the result is a hefty LES band. At
this time, it seems likely this band develops, the question that
remains is where it develops. To account for this, have included
very deterministic high-res model output before smoothing it out
across an smaller area than the last few days. For SLRs, latest
guidance was to increase these about 10% across the board, but I
only went up about 5% as model soundings show much the DGZ slightly
blo the greatest lift which is slightly elevated to start with this
event, before lowering as LES takes over. So expect SLRs to increase
through the duration of this event.

The result in snow totals from 00Z Sat through 00Z Sunday is a
widespread 6 to 9 inches across much of the UP, a small lull of 5 to
7 from L`anse to near Bessemer where the system snow tapers and lake-
enhanced doesn`t quite begin. Across the Keweenaw, two separate
enhanced bands are expected across this region so snow totals are
significantly higher. For northern Houghton and Keeweenaw counties,
expecting somewhere in the 9 to 13 inch range, with the potential
for up to 16 inches should any of these convergent bands remain over
any particular area. Ended up going with an advy for all of the cwa
to start for now, with the idea that LES across the Keweenaw and
potential enhancement off Lake Michigan will have a better grasp
with 12Z guidance. This would get the initial message out, while
still giving the day shift enough time to look into newest guidance
and upgrade to a warning if needed. At this time, seems the Keweenaw
has the best chance to go to a warning, but guidance differs enough
on location of convergent band that I wanted to wait until this
afternoon. LES snow doesn`t really get started before 00Z Sunday
across the east, so expect the discussion on that in the long-term

.LONG TERM...(Sunday night through Friday) Issued at 230 PM EST
FRI JAN 17 2020

Upper air pattern consists of a 500 mb ridge in the western U.S.
with a trough over the Great Lakes region 00z Sun. The ridge
amplifies 12z Sun over the west with troughing moving into New
England. Highly amplified ridge moves into the Rockies on Mon with
the trough digging into the ern U.S. Lake effect snow will be
winding down on Sunday with quieter and drier weather for Sun night
into Mon.

In the extended, the GFS and ECMWF show a 500 mb trough in the
western U.S. with a trough also across the ern U.S. with a ridge
across the plains 12z Tue. This ridge moves into the Mississippi
River valley 12z Wed. Troughing then moves into the plains 12z Thu
which moves into the upper Great Lakes 12z Fri. Temperatures for
this forecast period will go back above normal. Quieter and drier
weather lasts into Wed.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1236 PM EST FRI JAN 17 2020

Could be some briefly lower (MVFR) cigs at SAW late this afternoon
with SE upslope flow into the terminal but not sold on that
happening so kept it in a TEMPO for now. Otherwise, main story of
the TAF period will be the arrival of steady light snow tonight.
Have stair-stepped vis down into IFR tonight and then LIFR early
Saturday morning at CMX and SAW. LIFR vis definitely possible at IWD
as well but downslope SE flow may help keep snow just a little
lighter there so with it being late in the TAF period decided not to
include it for now. While some 1/2 to 1/4 mile vis is possible at
the terminals tomorrow morning, this will mostly be a drawn-out
light snow so we should stay above airfield minima for the most
part. Brief period of LLWS at IWD late tonight as well but it`s
marginal since downslope gusty winds at the same time will reduce
the overall shear magnitude.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 230 PM EST FRI JAN 17 2020

Southeast gale event across central and eastern Lake Superior still
on track for later tonight into Saturday afternoon. Next brief gale
events will be in the west Saturday evening with northwest gales to
35 knots. These are the two periods for strongest winds for this
forecast period. Otherwise, the wind stays below 30 knots.

Upper Michigan...
  Winter Weather Advisory from 9 PM EST /8 PM CST/ this evening to
     1 PM EST /noon CST/ Sunday for MIZ002-004-009-084.

  Winter Weather Advisory from 3 AM Saturday to 1 PM EST Sunday
     for MIZ006-007-014-085.

  Winter Weather Advisory from 10 PM this evening to 1 PM EST
     Sunday for MIZ001-003-005.

  Winter Weather Advisory from 9 PM EST /8 PM CST/ this evening to
     7 PM EST /6 PM CST/ Saturday for MIZ010>013.

Lake Superior...
  Gale Warning from 1 AM to 10 AM EST Saturday for LSZ249>251-266-

  Gale Warning from 1 AM to 7 AM EST Saturday for LSZ243>248-264-

Lake Michigan...


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