Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 192122

Area Forecast Discussion
National Weather Service Marquette MI
422 PM EST Mon Feb 19 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 421 PM EST MON FEB 19 2018

Water vapor imagery and RAP analysis show a deep trof over the
western CONUS (500mb height anomalies of 300m) and strong ridging
over the eastern CONUS (500mb anomalies of 300m over the ne). Result
is sw flow into the Upper Lakes. Although no significant shortwaves
are noted in the sw flow, upper jet dynamics and low/mid level fgen
are taking advantage of abundant moisture (precipitable water per
12z raobs was around 200pct of normal at KMPX/KGRB) to support areas
of pcpn across the Northern Plains to Upper Lakes. Focused fgen for
much of the day led to a band of mdt/hvy snow from nw WI to the
Houghton vcnty. Houghton area has probably had around 4in of snow
since mid/late morning.

SW mid level flow will remain in place thru the short term. With a
lack of any significant shortwaves lifting out of the western trof,
pcpn will continue to be largely driven by upper jet dynamics and
low/mid level fgen. Fgen supporting the heavier snow over nw Upper
MI is fcst to fade away this evening. Hvy narrow band of snow from
the morning/early aftn is already dissolving into a broader area of
mdt snow so that diminishing trend is underway. Meanwhile, there is
generally a consensus for a push of isentropic ascent across the
area this evening. As a result, pcpn should be more widespread thru
the evening hrs before diminishing in intensity and coverage. Pcpn
will probably become patchy overnight. In general, moisture depth
tends to diminish with time tonight in addition to continued waa
pushing an elevated warm nose above 0C northward into central and
eastern Upper MI. This should will lead to ptype becoming more
-fzra/-fzdz dominated with time. Sheared out shortwave will lift ne
across MN into northern Ontario on Tue. This may support another
period of more widespread pcpn Tue morning before pcpn diminishes
and mostly ends w to e in the aftn. Overall, ice accumulations over
the se half are likely to be under one-quarter inch and mostly one-
tenth to two-tenths of an inch...probably closer to the lower end of
that range. Ice accumulations will be less that that over the w.
Snow accumulations should range from less than 1 inch se to 2 to 4
far nw. Per coord with surrounding offices, advy for the central
will run until 00z Wed, but with pcpn largely done by 18z, will
likely be able to cut the advy end time back with later updates.

.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM EST MON FEB 19 2018

More active winter weather possible late this week into next weekend
as general troughing over west half of Conus contiues to send systems
toward Great Lakes.

Active weather occurring early this week settles down considerably
as early as Tue night as sfc low exits into Quebec and quasi
stationary boundary moves to the lower Great Lakes. High pressure
over northern Plains then builds over western Great Lakes through
Wed. Colder air (h85 temps down to -18c) works in on northwest low-
level winds so there may be light lake effect for northwest to west
flow snow belts. However, do not expect much LES this time around
since area is within dry slot of H85 low lifting toward James Bay
resulting in minimal large scale low-level moisture. Another
negative for LES is expansive ice on western Lk Superior. Will only
have slight chance pops for mainly the Keweenaw late Tue night into
Wed morning. Expect partly to mostly cloudy skies along Lk Superior
and east for much of the day but skies should clear out Wed night.
High pressure and light winds along with pwats less than 0.10 inch
point to min temps dropping well below zero inland. Used colder WPC
and GEM bias corrected guidance.

High pressure will keep conditions dry over Upper Michigan on Thu
though increasing high clouds will signal the return of another
system lifting into the region from the central Plains. Shortwave
and area of q-vector convergence with H85 wave and moisture
advection appear to be main drivers for the light snow. Not much
enhancement coming from upper level jet as its primary lifting
influence stays south and east of here closer to sfc front and
baroclinic zone. Real good agreement from model qpf and GEFS
ensembles for a 6-12 hour period of light snow with QPF amounts
staying less than 0.25 inch. SW flow ahead of H85 low tries to bring
warmer air into the western Great Lakes, but right now looks like it
stays cold enough for just snow as ptype across all of Upper

After a break on Sat, another system could move in late Sat night
into Sun as shortwave trough rides across the Great Lakes downstream
of broad trough aloft over west half of Conus. There are expected
model differences that far out though. Main difference is GFS taking
shortwave/sfc low farther south across the Ohio valley while
ECMWF/GEM and GEFS would bring system farther north across central
Great Lakes. Latest GFS continues to keep U.P. dry on Sun while
other guidance has at least light qpf over much of Upper Michigan.
ECMWF would even bring moderate qpf over 0.25 inch across parts of
Upper Michigan. Probably stays cold enough for just snow for this
system as well. Another weaker system may move in on Monday, but
there are too many differences to go with anything more than slight
chances. Other than chilly night Wed night, temps through the long
term should be normal or even above normal.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1227 PM EST MON FEB 19 2018

IFR conditions (vis and/or cigs) will mostly be the rule thru this
fcst period at KIWD/KCMX/KSAW as waves of pcpn move ne across the
Upper Lakes. While pcpn should be only snow at KIWD/KCMX, snow at
KSAW will likely mix with or change to -fzdz at times tonight thru
Tue morning. May even be a period of only -fzra Tue morning.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 242 PM EST MON FEB 19 2018

May see northeast gale gusts to 35 knots over western sections of Lk
Superior through tonight. Otherwise, winds are expected to stay
below gales the rest of the forecast period.

Upper Michigan...
  Winter Weather Advisory until 7 PM EST /6 PM CST/ Tuesday for

  Winter Weather Advisory until 1 PM EST /noon CST/ Tuesday for

Lake Superior...
Lake Michigan...


SHORT TERM...Rolfson
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