Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 121818

Area Forecast Discussion
National Weather Service Marquette MI
218 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 through Sunday)
Issued at 418 AM EDT MON MAR 12 2018

The main issue in the extended portion of the forecast will be the
potential for moderate lake effect snow over mainly north-central
and eastern portions of the U.P. through Tuesday afternoon.

Tuesday into Tuesday night: An upper-level closed low is progged to
slide southeast from eastern Upper MI and southern Ontario into the
lower Great Lakes through this time period. This will help to
intensify a broad surface low off the east coast. At the same time,
a strong surface high is progged to strengthen over the northern
Plains. Between the two systems, the U.P. will be in a tighter
pressure gradient, allowing for stronger north to north-northwest
flow through Tuesday evening. The combination of strong low level
flow, along with 850mb temperatures around -16C Tuesday and Tuesday
evening, will lead to a continued increase in lake effect snow
potential for north to north-northwest wind favored snow belts.
There will be a fairly deep layer of moisture in the DGZ, which will
help to boost SLRs across the north-central and eastern portions of
the U.P. during this time period. This will set the stage for final
snowfall totals from Monday through Tuesday evening of around 4 to 8
inches over the high terrain north-central and 1 to 4 inches
elsewhere downwind of Lake Superior. The snow will be fluffy, so the
gusty north to north-northwest winds will allow for some blowing and
drifting snow, especially along Lake Superior. Again, the heaviest
snowfall totals will likely be in the high terrain of the north-
central U.P. where upslope creates additional lift.

Wednesday through Thursday night: The aforementioned dry high
pressure ridge over the Plains will slide into the area briefly late
Tuesday night into Wednesday morning. Then on Wednesday afternoon
and evening a quick moving wave will slide through the area. This
will give a few lake effect snow showers across the north central
and eastern U.P. on a quick shift back to north to northwest winds.
Inland and portions of the western and south central U.P. will see
quite a bit of sunshine during this time period. Temperatures will
also be near to slightly above normal.

Friday through Monday: Models begin to diverge significantly during
this time period, which is not too uncommon. The GFS would have some
light precipitation developing on WAA into the area Friday night
into Saturday; however, the EC is very dry during the same time
period and holds off on the precip until Sunday night into Monday.
At this point, with the increased model differences, will stick with
a consensus of the models.

.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
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