Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 121847

Area Forecast Discussion
National Weather Service Marquette MI
247 PM EDT Mon Mar 12 2018

.SHORT TERM...(Today and tonight)
Issued at 509 AM EDT MON MAR 12 2018

Water vapor imagery and RAP analysis show sharpening nw flow over
the area as a shortwave and upper jet streak dive into the Great
Lakes. Snow associated with the shortwave has largely exited the
fcst area, but some trailing shsn are occurring, especially where
wnw winds upslope more strongly. Subsidence behind the shortwave is
leading to clearing skies over western Lake Superior as 850mb temps
are currently only -7 to -8C, not low enough to support any LES.

Mid-level trof will continue to expand over the Great Lakes today.
Meanwhile, 850mb temps will slowly fall, dropping to -12 to -13C
across Lake Superior by 00z. Considering the higher mid Mar sun
angle and air mass only cooling to become marginally cold enough for
LES, will likely see a hybrid type LES develop during the day -- a
situation where moisture off the lake combines with steepening low-
level lapse rates over the land to generate shsn that are more land-
based rather than lake-based. Cooling at the mid levels and being on
the cyclonic side of the upper jet will also support the shsn. These
snow showers should be more numerous over the western fcst area
rather than eastern fcst area this aftn as upsloping should further
aid development. Snow accumulations today will likely be under 1

Tonight, one shortwave will pass across the western fcst area during
the first part of the night, followed by a second dropping to
central Lake Superior by 12z Tue. Continued cooling at 850mb
combined with deep layer forcing from the wave will result in
expansion/intensification of shsn this evening. Then, thru the
night, nocturnal cooling and 850mb temps falling to -15 to -18C will
result in more traditional LES organizing in the n wind favored snow
belts. Have some concerns about ice cover utilized in the models and
how it affects the LES generated. The ice on the lake has become
more broken up in recent weeks and shouldn`t act as a solid sheet
that inhibits heat/moisture fluxes. As a result, LES accumulations
tonight could be greater than reflected in this fcst, especially
with the deep cold air under troffing leading to lake induced
equilibrium levels up to 8-10kft and DGZ well positioned in the
convective layer. For now expect, greatest accumulations over the n
central where upslope n wind and longer fetch should easily support
decent coverage of 3-5in/12hr snow accumulations with locally higher
amounts. Thus advy was issued for Marquette/Alger counties. To the
w, n wind will favor the high terrain of Keweenaw County and
Gogebic/Ontonagon Counties. Ice cover is more substantial off
western Upper MI, but with the ice cover probably not as great as
modeled and not inhibiting heat/moisture fluxes as much as models
indicate, snow accumulations could be a surprise over the w tonight.
Bumped up accumulations more solidly into the 2-4 inch range for

.LONG TERM...(Tuesday night through Monday)
Issued at 247 PM EDT MON MAR 12 2018

Upper air pattern consists of a 500 mb trough on the west coast,
closed low in the lower Great Lakes and a ridge over the Rockies 00z
Wed. There is also a shortwave over northern Manitoba that drops
southward Tue night and moves into the lower Great Lakes Wed night
into Thu.

In the extended, GFS and ECMWF show a 500 mb trough over New England
and another over the western U.S. 12z Fri. The trough in the western
U.S. moves little through Sun while the ern U.S. begins to get into
some upper level ridging. Troughing moves into the Rockies on Mon.
Temperatures remain near normal for this forecast period and will be
fairly quiet.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 215 PM EDT MON MAR 12 2018

Increasingly colder air moving into the Upper Great Lakes combined
with a disturbance dropping over the area will lead to increasing
shsn during this fcst period. Initial MVFR conditions at
KIWD/KCMX/KSAW will trend down late this aftn into this evening
with the development of widespread shsn. These shsn will increase
tonight with northerly winds likely leading to poorest conditions
at KSAW/KIWD where IFR conditions should occur overnight. The IFR
conditions could develop as early as the evening hrs. Improvement
is expected at all TAF sites by late Tue morning as a high pressure
ridge builds in from the west.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 509 AM EDT MON MAR 12 2018

Strongest winds across Lake Superior will be in the 20-30kt range
this aftn through Tue morning, strongest across the east half of the
lake. Winds for the rest of the week will mostly be at or blo 20kt
though a few periods of winds up to 25kt will occur. No gales

Upper Michigan...
  Winter Weather Advisory from 6 PM this evening to 5 PM EDT
     Tuesday for MIZ005-006.

Lake Superior...
Lake Michigan...


SHORT TERM...Rolfson
MARINE...Rolfson is the U.S. government's official web portal to all federal, state and local government web resources and services.