Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200724

Area Forecast Discussion
National Weather Service Marquette MI
224 AM EST Tue Feb 20 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...(Wednesday through Monday)
Issued at 224 AM EST TUE FEB 20 2018

Upper air pattern consists of a 500 mb trough in the western U.S.
and a strong 500 mb ridge over the sern U.S. 12z Wed. The trough in
the western U.S. tries to advance eastward, but the shortwaves that
eject out of it get sheared out as the ridge remains over the sern
U.S. this forecast period. 850-500 mb q-vector convergence and some
deeper moisture arrives Thu night. Looks pretty quiet until Thu
night when next system arrives. Did not make too many changes to the
going forecast.

In the extended, GFS and ECMWF show a 500 mb trough over the western
U.S. 12z Fri extending up into the Canadian Prairies and a 500 mb
ridge across the sern U.S. The trough ejects into the southern
Rockies 12z Sat and into the Great Lakes Sat night. More troughing
moves into the area 12z Mon into Mon night. Temperatures stay above
normal for this forecast period. System moves out Fri with another
coming in Sat night and another on Mon.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1231 AM EST TUE FEB 20 2018

IFR conditions (vis and/or cigs) will mostly be the rule into Tue
morning this fcst period at KIWD and KCMX 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. IFR conditions at KSAW will likely lower
to LIFR late tonight and Tue morning. May even be a period of only
-fzra Tue morning. Expect slowly improving conditions Tue afternoon
and evening as pcpn generally ends and cigs rise to low end MVFR.

.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/ this evening
     for MIZ004>007-010>014-085.

  Winter Weather Advisory until 1 PM EST /noon CST/ this afternoon
     for MIZ001>003-009-084.

Lake Superior...
Lake Michigan...


SHORT TERM...Rolfson
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