Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180746

Area Forecast Discussion
National Weather Service Marquette MI
246 AM EST Sun Feb 18 2018

.SHORT TERM...(Today and tonight)
Issued at 246 AM EST SUN FEB 18 2018

Upper air pattern consists of a 500 mb trough in the Pacific NW,
zonal flow across the west half of the U.S. and a shortwave over the
lower Great Lakes this morning. The trough in the Pacific NW digs
southeast into the western U.S. by 12z Mon as a ridge retrogrades
back towards the southeastern U.S. Nam brings in some 850-500 mb q-
vector convergence this afternoon which remains through tonight
along with deeper moisture, but most of the moisture is to the north
of the area. This is the trend as it looks slightly drier than
before, so will make some slight adjustments downward on the
southward extent of pops and also lighter amounts of qpf. Still
looks like advisory amount of snow for the Keweenaw and will not
change timing at all. This would be the only spot that would need
to have an advisory out of this event.

.LONG TERM...(Sunday night through Saturday)
Issued at 438 PM EST SAT FEB 17 2018

Active period of winter weather still expected into Tuesday. Ptype
may be more of an issue for more areas, especially Mon night into

Summary on expected weather and possible headlines Mon into Tue:
Headlines will likely be needed over all of Upper Michigan at some
point. A winter storm warning for just warning criteria snowfall
seems unlikely, however with models trending toward more mixed
precipitation and ice, could see warning at some point due to
moderate wet snow amounts and/or significant ice accums,
especially south and east. Would imagine most headlines for this
event will come out later tonight or on the dayshift on Sunday.

Lead system that brings snow over mainly northwest Upper Michigan
exits after midnight over eastern forecast area. Could see brief
uptick in the snow east of Marquette toward eastern U.P. with
increasing moisture advection and continued lift in right entrance
region of jet over northern Ontario and Quebec. Could see some light
freezing drizzle as the light snow tapers off and before next round
of light snow begins to move in over western U.P. late.

Mon into Mon night system still looks complicated to project mainly
due to two jet streams (polar and sub-tropical) that will be coming
together to bring the system into the Upper Great Lakes. Most of the
precip initially upstream of Upper Great Lakes on Mon morning will
be along sub-tropical jet in form of rain/freezing rain across mid
Mississippi River Valley while the main area of snow will be
expanding from the northern Plains to south half of MN and into
north half of WI on front side of larger troughing aloft and in H85-
H7 gen area in right entrance of polar jet from northern Plains to
Quebec. Though main sfc low and even sfc trough stays well to the
south of Upper Michigan (only as far north as southern WI into lower
Michigan) Mon into Mon night, fgen forced snow enhanced by
divergence aloft from upper jet and convergence along H85 trough
axis from near Omaha to south central Upper Michigan should expand
across Upper Michigan through the day. Potential for heavy snow
looks on the lower side as strongest moisture advection stays south
and east of Upper Michigan closer to the sfc low/trough and there is
not a stronger shortwave trough/deformation area that lifts across
the area. At this point, seems best shot at seeing warning snowfall
amounts will be over western Upper Michigan where there is less
chance of any mixed precip throughout and where SLRs may end up a
bit higher. WPC probabilistic winter guidance shows highest
probabilities for seeing at least high end advy for those areas as

Another wrinkle that is starting to show up is that most models now
show lack of ice nucleation occurring outside of when main area of
snow moves through late Mon morning into Mon afternoon. If that is
true, there would be more freezing drizzle or light freezing rain
over at least the south and east late Mon aftn through Mon night.
Some guiance would have freezing precip even as far west as Iron to
Baraga county on Mon night. That is a change from recent model runs.
Next low pressure wave lifts along the existing sfc boundary late
Mon night into Tue. Possible that our far southeast zones may see
0.10 to 0.20 inch of qpf from this next segment of this drawn out
system. Soundings indicate lack of ice aloft though and even if
there is deeper moisture, a farther north warm layer aloft is now
showing up. ECMWF increases H85 temps to around +5c over eastern
forecast area on Tue. While that warm layer aloft is present, sfc
temps are in the 20s. Freezing rain looks likely or maybe sleet if
warm layer is more 1-3c. Even more significant icing may occur
farther south into WI deeper into the heavier qpf from this next
wave. But, we are looking at more freezing rain and icing issues
even into our area. Widespread wintry precip should exit eastern
area Tue night with just some light lake effect possible into Wed as
cooler air moves across. High pressure will bring drier weather late
this week before another system brings mainly light snow to the area
by next weekend.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1202 AM EST SUN FEB 18 2018

Expect VFR conditions to prevail at at all sites into Sunday
morning. Light snow will move into the west at KIWD/KCMX by late
Sun morning with MVFR and possibly IFR vsby Sun afternoon. Best
chance for IFR vsbys will be at KCMX. Snow may stay far enough nw to
keep vsbys mostly VFR at KSAW. Cigs will lower to MVFR Sun
afternoon and should stay that way into Sun evening.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 246 AM EST SUN FEB 18 2018

South gales to 35 knots are expected over northern Lake Michigan
late this afternoon into this evening. Otherwise, winds are expected
to stay below gales through the rest of the forecast period.

Upper Michigan...
  Winter Weather Advisory from 9 AM this morning to 1 AM EST
     Monday for MIZ001-003.

Lake Superior...
Lake Michigan...
  Gale Warning from 4 PM this afternoon to 1 AM EST Monday for



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