Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 141015

Area Forecast Discussion
National Weather Service Marquette MI
615 AM EDT Sat Apr 14 2018

.SHORT TERM...(Today and tonight)
Issued at 615 AM EDT SAT APR 14 2018

Moderate snow will continue over the next few hours near Menominee
and far southern Menominee county, so extended the advisory until

Otherwise, attention turns to the upcoming storm system that will
bring snow to the area starting late tonight. All or most of the
snow moves in after 06Z, but in that last 6 hours of the short term
period, up to 4-6" of snow is expected along the WI border, with 1-
3" expected over much of the rest of the U.P. Snow Ratios will be
near 10:1, so the snow will be dense and make travel and snow
removal more difficult. Gusty winds will continue through the short
term with inland gusts of 25-30mph and shoreline gusts of 30-40mph.
This will lead to blowing snow where/when fresh, blowable snow
exists...further hindering travel. In coordination with other
offices, watches were upgraded to Winter Storm Warnings starting
late tonight and going through Sun night. Most of the impacts with
this system are in the long term (see discussion below for more

With the prolonged and strong E-NE winds, ice shoves and ice jams
are a concern...mainly on NE-E facing areas such as Marquette
through the E side of the Keweenaw.

.LONG TERM...(Sunday through Friday)
Issued at 602 AM EDT SAT APR 14 2018

An active/progressive pattern will be the rule thru the upcoming
week as a series of vigorous shortwaves track off the N Pacific and
then across the CONUS underneath mean positive height anomalies
setting up across central and eastern Canada. Biggest pcpn producer,
a widespread significant snowfall for Upper MI, will occur later
tonight thru Sun as a deep trof lifts across the Great Lakes/Ohio
Valley. Next shortwave reaching the W Coast Mon will track to the
western Great Lakes at the middle of the week. Pcpn, snow or
rain/snow, with this system will be much lighter than its
predecessor given limited time for return flow in the wake of the
prior, more substantial trof. However, given what could be quite a
vigorous wave, there may be a stripe of mdt pcpn forced just n of
the shortwave track. A third shortwave reaching the W Coast Wed/Thu
may reach the western Great Lakes late week or over the weekend. As
for temps, blo normal temps will prevail thru the upcoming week,
though with time, the magnitude of temp departures will decrease
overall as anomalously deep mid-level low currently shifting e from
Hudson Bay and across Quebec departs and is replaced with above
normal heights. This will eliminate the source of very cold air for
Apr that currently exists not too far to the n of here. Keep in mind
that normal high temps are moving up thru the upper 40s and 50s over
the next 7 days.

Beginning Sun/Mon, models have moved to much better agreement for
the late season winter storm to impact Upper MI as they have trended
to the ECMWF/NAM solution in being much more aggressive in pushing
hvy pcpn into Upper MI. There are still some issues to sort thru,
but the overall expectation is for a significant late season
snowfall to impact the fcst area. Strong deep layer forcing and a
strong surge of isentropic ascent with copious moisture will swing
across Upper MI during the day Sun. Mixing ratios of 4-6g/kg in the
700-750mb layer will be advecting in the isentropic ascent zone
swinging n across the area, supporting the potential of 6-9 or 8-12
inch snowfall for the approximate 9 or up to 12hrs of strong ascent.
The DGZ is well aloft, in the 13-20kft agl layer, with a narrow low-
level DGZ, mainly across the central and w. As a result, snow-to-
water ratios will likely be low, probably on the order of 9-13 to 1
with strong winds thru the low-mid levels working to break up the
dendrites during a long fall. ENE 950mb winds of 30-40kt will add an
upslope component to the snowfall over the higher terrain of n
central Upper MI, Marquette/Baraga counties to the w of the city of
Marquette. Could be some lake enhancement, but temps are marginal
and with winds at and above 850mb backed to the e, it`s not a good
set up. Nonetheless, expect the upsloping to lead to a local
snowfall max in the aforementioned higher terrain n central.
Finally, the NAM introduces the unfortunate possibility of ptype
other than snow over the eastern fcst area as it drives a well-
elevated (around 700-750mb) above freezing warm nose (up to 2C) into
that area, leading to the potential of a lot of sleet. None of the
other models are that aggressive with the warm nose, but the
regional CMC is closest. Don`t have all the CMC level data, but it
does push 700mb temps just above 0C from Manistique to Whitefish Pt.
For now, will downplay the sleet potential, but will show lowest
snow ratios in that area, which will knock snow totals down a bit in
that area.

Across the area, the lower snow-to-water ratio snow will make the
snow more difficult to shovel/plow. Signal in the models is for snow
to fall very heavily for roughly a 6hr period at most locations, so
where plowing does not occur, travel will become extremely
difficult, especially considering the denser nature of the snow.
Brisk/gusty winds will produce blsn/drifting snow as well, further
reducing vis during hvy snowfall. Snow may not be wet enough to
stick sufficiently to trees/power lines to cause any additional
issues with downed limbs/power outages. Finally, the normal seasonal
water level decline on Lake Superior has lowered water levels
roughly a foot from the abnormally high levels of last fall. Still,
there may be some minor beach erosion where shore-fast ice has
thinned or disappeared. Where shore ice exits, large waves impacting
the ice could send large sections of ice well up on beaches,
potentially damaging any property close to the shore. Beaches
oriented perpendicular to ene winds will be most susceptible along
with bays open to the waves.

Mdt/hvy pcpn will have lifted mostly n and e of the area by 00z Mon,
leaving behind lighter pcpn. Still looks like there could be a loss
of ice in the cloud deck as the pcpn winds down Sun evening under
mid-level drying, mainly across roughly the eastern 1/3rd of the
fcst area. This may lead to a little -fzra or more likely some
-fzdz. Elsewhere, ocnl -sn will continue, most persistently in areas
that see upsloping under low-level ene winds backing more northerly.
Additional snow accumulations of 1 to perhaps as much as 3 inches
could occur in those areas. NAM indicates another surge of pcpn
lifting nw into the e half of Upper MI overnight in the circulation
around broad mid-level low drifting to Lower MI or IN. It is the
only model indicating this and will be dismissed for now. If it
should occur, it would bring another burst of snow of 2-4in.

Lingering light pcpn will diminish/end Mon into Tue morning.
Aforementioned shortwave to arrive midweek could be an interesting
system. Models depict a vigorous wave accompanied by steep mid-
level lapse rates that may be able to generate a fairly narrow
stripe of mdt to perhaps hvy pcpn just n of the shortwave track.
Operational and ensemble guidance is not narrowed in on the track of
wave, but Upper MI is certainly within the area that could be
impacted. If wave does track just s of the area, another
accumulating snowfall will be in the offing.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 122 AM EDT SAT APR 14 2018

All sites should be VFR through the period. Winds will be
increasing later tonight into Saturday ahead of the advancing
low pressure system.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 615 AM EDT SAT APR 14 2018

As a strong low pressure system slides toward the area through the
weekend, winds will continue to increase across Lake Superior. Gales
of 40-45 knots are expected over Lake Superior into Sunday night.
Gales will slowly diminish to 30 kt winds Sunday night into Monday.
Winds for the rest of next week should settle down below 25 kts.
Heavy freezing spray will be an issue through the weekend.

Upper Michigan...
  Winter Storm Warning from 2 AM EDT /1 AM CDT/ Sunday to 8 AM EDT
     /7 AM CDT/ Monday for MIZ001>006-009-084.

  Winter Storm Warning from 2 AM EDT /1 AM CDT/ Sunday to 2 AM EDT
     /1 AM CDT/ Monday for MIZ007-010>014-085.

  Winter Weather Advisory until 10 AM CDT this morning for MIZ012.

Lake Superior...
  Heavy Freezing Spray Warning until 4 PM EDT this afternoon for

  Gale Warning until 2 AM EDT /1 AM CDT/ Monday for LSZ162-240>251-

Lake Michigan...
  Gale Warning until 8 PM EDT Sunday for LMZ221-248-250.



LONG TERM...Rolfson
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