Area Forecast Discussion
Issued by NWS Marquette, MI

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914
FXUS63 KMQT 172139
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
439 PM EST Sat Feb 17 2018

.SHORT TERM...(This evening through Sunday)
Issued at 410 PM EST SAT FEB 17 2018

WV imagery and RAP analysis indicated cyclonic wrly flow through the
n cntrl CONUS around a deep mid/upper level low west of Hudson Bay.
A shortwave trough over WI supported an area of light snow that has
from far srn Upper MI through ern WI into nrn IL. Drier low level
air further north has limited coverage of the pcpn into the rest of
the cwa. Another signficant upstream shortwave was moving through
the Pacific Northwest.

Tonight, any remaining snow over the far s or se cwa will move out
during the rest of the afternoon, per radar/satellite trends.
Otherwise, favorable radiational cooling conditions overnight should
allow temps to drop into the single digits over inland locations
before mid/high clouds increase from west to east late.

Sunday, a broad area of WAA and isentropic lift will strengthen as
the shortwave move through the nrn plains. Models suggest that the
heaviest band of snow will move through nrn MN into wrn Lake
Superior and mainly the Keweenaw Peninsula. There is still some
uncertainty with the snowfall amounts as the ECWMF/NAM and
regional GEM remained or trended farther north compared to the GFS
with higher QPF axis. So, an advisory was issued only for the
Keweenaw where the highest amounts are likely. With 2-3g/Kg
moisture avbl and a period of intense lift and mid level fgen,
local amounts in the 3 to 6 inch range will be possible. Farther
south amounts should range from 1 to 3 inches over most of the
rest of the nrn half of Upper Michigan.

.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
Tue.

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
well.

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 18Z TAFS through 18Z Sunday afternoon)
Issued at 115 PM EST SAT FEB 17 2018

MVFR cigs at KCMX adied by some lake moisture in wsw flow are
expected to give way to VFR conditions by mid afternoon as drier air
moves in. VFR conditions should then 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 by the end of the
period. Cigs should remain MVFR.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 410 PM EST SAT FEB 17 2018

A few southwest gale force gusts to 35 knots are expected Sunday
night over eastern Lake Superior. Otherwise, winds are expected to
stay below gales through the rest of the forecast period.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory from 9 AM Sunday to 1 AM EST Monday for
     MIZ001-003.

Lake Superior...
None.
Lake Michigan...
  Gale Warning from 4 PM Sunday to 1 AM EST Monday for LMZ248-250.

&&

$$

SHORT TERM...JLB
LONG TERM...JLA
AVIATION...JLB
MARINE...JLB



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