Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 240451

Area Forecast Discussion
National Weather Service Marquette MI
1251 AM EDT Mon Apr 24 2017

.SHORT TERM...(This evening through Monday)
Issued at 343 PM EDT SUN APR 23 2017

12Z raobs/latest wv imagery and RAP analysis show a confluent wnw
flow alf over the Upr Lks btwn nrn branch troffing centered over
Hudson Bay and a zonal srn branch flow dominating the CONUS. The
cold fnt which swung thru Upr MI late last ngt/early this mrng has
pushed into scentral WI and stalled, but the frontal bndry at h85-7
is still nearly ovhd and supporting a bkn band of rain/snow showers
over the wrn cwa. Sfc hi pres bldg into nw Ontario is extending a
sfc rdg axis over Lk Sup, and the llvl drying/sharper acyc flow
associated with this feature has brought some clrg to that portion
of the cwa. Very dry air is also located to the s of Upr MI even
over the stalled sfc fnt. Looking well upstream, a vigorous shrtwv
that caused 12hr h5 hgt falls of nearly 100m in the srn stream flow
is moving into the central Rockies.

Tngt...As the srn branch shrtwv now moving into the Rockies
aprchs the wrn Plains late, a sfc lo pres is fcst to deepen over
the ncentral Plains while the hi pres over northern Ontario drifts
slowly to the e. As the flow alf veers to the s in response to
the falling mslp to the w, the fntl bndry that stalls to the s wl
return to the n. The associated isentropic ascent best shown on
the 290-295K sfcs (h8-7) wl support some lgt pcpn generally in
the form of snow over mainly the nw half of the cwa away fm drier
llvl air over the e, but the steady shift to the n of the warm fnt
and influence of the llvl dry air wl limit pops/pcpn amnts. The
presence of a good deal of lingering clds over the w and incrsg
hi/mid clds over the e associated with the waa wl limit the
diurnal temp drop despite the llvl dry air.

Mon...The shrtwv/lo pres in the ncentral plains is fcst to drift ne
toward nw MN late in the day, lifting the sfc warm fnt and band of
waa pcpn to the n of Upr MI. The short range guidance shows quite a
bit of mid lvl drying in the warm sector. With the prospect of at
least some sunshine thru hi clds and h85 temps rising to arnd 5C,
temps should rise well into the 50s, especially in the downslope
areas influenced by the llvl se flow, where readings wl probably
reach the 60s. Tended toward the hier end of guidance for temps.
More clds/at least sct showers could arrive over the far w late in
the day as the lo pres/deeper mstr and stronger forcing ahead of the
shrtwv aprch.

.LONG TERM...(Monday night through Sunday)
Issued at 351 PM EDT SUN APR 23 2017

The main forecast highlights through the week remain the active
pattern advertised by the medium range models, which will bring
multiple chances for precipitation across the area. Winter weather
is expected to make a return with freezing rain, sleet, and snow
possible through the middle/end of the week. There is still quite
a bit of uncertainty, so continue to monitor the forecast!

Monday night into Tuesday, low pressure will continue to lift
northeast towards western Upper Michigan as a couple of weak
shortwaves lift northeast across the region. As the better lift and
deeper moisture arrives, expect rain to begin across the west early
Tuesday morning. Further to the east and south, mid-level air looks
far too dry for any overnight precipitation. Through the day on
Tuesday, precipitation will begin to wane across the west; however,
a north to south oriented surface trough is expected to remain
anchored across the central portions of Upper Michigan. This surface
trough will become further enhanced Tuesday evening and overnight as
additional shortwave activity lifts across the region, bringing back
precipitation chances across much of the area. Precipitation type
will also be an issue as the upper-level flow continues to remain
quasi-parallel to the surface trough, making the Northern Great
Lakes serve as a pivoting point between the colder Canadian air
dropping southeast and warm, moist air lifting northeast. Tuesday
evening into the overnight hours, precipitation is expected to
remain all rain as surface temperatures through the low levels
remain above freezing. However, there will be a transition over to
freezing rain and sleet as colder Canadian air undercuts the warm
moist air across the west on Wednesday morning and may push east
into portions of central Upper Michigan. Forecast soundings show the
potential for limited cloud ice at times; therefore, we could see
more freezing drizzle than rain across the west. For simplicity and
consistency have opted to leave it as freezing rain for now. Warming
surface temperatures over the past few weeks will also complicate
ice accumulations, albeit still possible, especially on elevated
surfaces. Impacts from this wintry mix of precipitation will be
highly dependent on the longevity and intensity of freezing rain.

Precipitation is expected to linger through much of the day on
Wednesday. However, confidence is much lower in how things will
evolved on Wednesday with precipitation type across the central
portions of the area. With the colder, shallow air continuing to
move east with time, did opt to run with non-diurnal temperature
which did push some mentions of freezing rain across portions of
central Upper Michigan. Wednesday night through Thursday, as the
main longwave trough beings to lift northeast out of the central
Plains, the elongated surface trough draped across the region will
transition from an open wave to a maturing system. As this
occurs, there is the potential for locations across Upper Michigan
to see accumulating system snow and freezing rain as this system
tracks across the region; however, this will be highly dependent
on the track of the system. The medium range models track the
system anywhere from the western U.P. to eastern U.P. overnight
Wednesday into Thursday. The further east track would be more
favorable for system snow across the west and possibly central
portions of the area. However, if the system were to take the
western most track, much of the area may be dry slotted during the
day Thursday. Considering the variety of plausible solutions, not
comfortable pinpointing any specific amounts or areas that may
see system snow at this time. However, this is definitely a time
period that needs to be monitored as the system continues to
develop and evolve over the next few days.

Depending on when the track of the system, precipitation chances may
linger through the day on Thursday before gradually coming to an end
from south to north as the system finally exits the region and moves
north of the Hudson Bay. Friday looks mostly dry as high pressure
briefly moves overhead. This weekend the active weather will
continue with additional chances for precipitation. The GFS is much
more aggressive bringing precipitation back north on Saturday,
whereas, the ECMWF is much slower.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1251 AM EDT MON APR 24 2017

A northward lifting band of -sn may affect KCMX for the next hr or
two. Otherwise, dry low-level air mass will dominate the area thru
today, allowing VFR conditions to prevail at KIWD/KCMX/KSAW. Winds
will become gusty to 20-25kt at all terminals this aftn.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 351 PM EDT SUN APR 23 2017

N winds up to 20 kts over the e half of the lake will diminish this
evening as a hi pres ridge builds over the Upper Lakes. As this
ridge shifts to the e and a deepening lo pres in the Plains moves
toward MN, expect winds to veer toward the e-se and increase up to
30 kts on Mon. Where the winds will be strongest over the ncentral,
there could be a gale. Winds will veer southeasterly overnight at 20
to 30 knots before gradually diminish to 10 to 15 knots across the
western half of the lake by Tuesday morning. Further central and
east, expect the southeast winds of 20 to 30 knots to persist. A few
gale force gusts to 35 knots are possible early Tuesday night.
Northeast gales of 35 knots look likely across much of the lake as
the pressure gradient increases behind an exiting surface trough
late Tuesday night through Wednesday. It is possible these winds may
hold on through Wednesday night into Thursday, especially across the
central and eastern portions of the lake. By Friday morning, winds
will back west-northwest and diminish to around 10 to 20 knots.
These winds will continue through the weekend, but veer to the east-

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Ritzman
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