Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 222346

Area Forecast Discussion
National Weather Service Marquette MI
746 PM EDT Sat Apr 22 2017

.SHORT TERM...(This evening through Sunday)
Issued at 324 PM EDT SAT APR 22 2017

12Z raobs/latest wv imagery and RAP analysis show a split flow
dominating the wx pattern over NAmerica. Upr MI is on the srn flank
of a nrn branch flat upr trof centered near Hudson Bay. A shrtwv
embedded in this flow is tracking acrs far nrn Ontario, with
attendant sfc cold fnt stretching fm sfc lo pres aprchg srn James
Bay into nrn MN. Due to the warmth/dryness of the airmass ahead of
this bndry per local 12Z raobs that has supported max temps into the
60s/rh falling as lo as about 20 pct over the cwa, there is an
absence of pcpn and even much cld cover ahead of the slowly aprchg
cold fnt. But on the cold side, there is a solid ovc and some light
ra that changes to sn under a band of h7 fgen and with an influx of
much colder air ahead of 12Z h85 temps as lo as -15C at The Pas

Tngt...Lingering dry air associated with sfc hi pres retreating
slowly to the se wl bring dry wx early in the evng, but then
incoming cold fnt associated with the disturbance in the nrn branch
tracking thru Ontario wl reach the Keweenaw by 03Z and then the far
scentral arnd 12Z Sun. The band of pcpn under axis of h7 fgen on the
cold side of the fnt wl arrive over the far nw cwa toward midngt and
influence mainly the nrn tier with an upslope nly flow in the wake
of the fropa. Although the pcpn, which wl start as ra but then mix
with sn as colder air follows, wl be relatively light with an
absence of sgnft mstr inflow and passage of sharper dynamic forcing
to the n closer to the shrtwv track, there could be some wet sn
accum over the hier terrain of nw Upr MI as min temps dip to 32.

Sun...Hi pres bldg into nw Ontario under larger scale subsidence
following the exiting shrtwv is fcst to extend a sfc rdg axis into
the Upr Lks. Although the arrival of this rdg axis/some drier llvl
air and acyc flow as well as weakening fgen wl tend to diminish any
pcpn over mainly the nrn tier persisting in the mrng, a good deal of
mid lvl mstr/cld cover wl linger near an h85-7 fntl bndry that
remains near the area to the n of the sfc fnt that wl stall in WI.
The best chc for some partial clrg in the aftn wl be over the ne
cwa, which wl be more influenced by deeper drying. Did retain some
lo chc pops thru the aftn over the w, where the drying wl be less
emphatic. H85 temps falling as lo as arnd -6C over the Keweenaw and
llvl nly flow off Lk Sup wl cause much cooler wx for the cwa, with
hi temps holding in the 30s near Lk Sup.

.LONG TERM...(Sunday night through Saturday)
Issued at 333 PM EDT SAT APR 22 2017

With an active patterned expected through next week, we will see a
roller coaster of temperatures with periodic chances for
precipitation, including the potential for some snow.

Sunday night through Monday morning, as upper-level energy lifts
northeast of the area and flow becomes zonal across the region, the
cold front that pushed south across the area on Sunday will stall
out across central Wisconsin and lower Michigan. Upstream of the
region, another system is progged to develop in the lee of the
Rockies and lift northeast across the central Plains by Monday
morning. Ahead of this system, warm air advection will begin to lift
back north across the area. This elevated frontal zone will bring
precipitation chances back to the area, especially across the west
and north central. With the stalled out surface boundary expected to
be south of the area, we will be on the cooler side of the boundary.
Therefore, the combination of overrunning warm air and a pocket of
colder air at low levels may promote the potential for a wintry mix
of precipitation, including freezing rain, sleet, and snow. However,
the dominant precipitation type will be highly dependent on the
depth of the cold air at low levels and surface temperatures. During
the day on Monday, the stalled front across central Wisconsin and
lower Michigan will lift back north and allow for warmer air to
overspread Upper Michigan, as the above mentioned low pressure
system lifts northeast across the Upper Mississippi Valley. As
temperatures warm, any lingering precipitation will transition over
to light rain/drizzle. There should be a break in precipitation
during the afternoon and evening hours on Monday as we break out
into the warm sector.

As this surface low lifts north precipitation chances will return
Monday night and Tuesday as shortwave energy lifts across the area.
This surface low is expected to weaken as it traverses the region,
leaving behind a slow moving frontal boundary across the region, and
extending down into the southern Plains, as mid-level flow becomes
parallel to this boundary. Uncertainty does exists among the medium
range models as to how far east the precipitation will get during
the day on Tuesday, as the ECMWF is a bit more progressive with the
eastward movement of the frontal boundary. At the same time, low
pressure is expected to develop along the tail-end of the slow
moving frontal boundary down across the southern Plains as a deep,
longwave trough digs across the rockies and ejects out across the
Plains. This developing system will lift northeast towards the
region Tuesday night through Wednesday. This will allow
precipitation chances to increase across Upper Michigan, especially
Wednesday morning and through at least the rest of the day.

While there is uncertainty among the models and ensembles in regards
to the track and strength of the system, forecast soundings from the
GFS/ECMWF do advertise thermal profiles becoming cold enough to
support snow, at least across the western portions of Upper Michigan
on Wednesday. Further to the east, medium range models showing
temperatures aloft remaining just warm enough for precipitation to
remain all liquid, but a transition over to snow sometime Wednesday
night into Thursday looks possible as cold air advection increased
on the back side of the exiting low pressure system. As mentioned
above, there is quite a bit of uncertainty with this system and the
details will likely change over the next few days, but this time
period is something to monitor.

The end of the week and beginning of the weekend look near normal
temperature wise with high pressure dropping down from Canada.
Precipitation chances look low at this time, with the deterministic
models keeping precipitation well south of the area.

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 746 PM EDT SAT APR 22 2017

A cold front will drop s across the area tonight, passing KCMX this
evening and KIWD/KSAW overnight. Low clouds/IFR and even LIFR cigs
along with some -ra changing to -sn will impact the terminals
following the fropa and into Sun morning before the arrival of
somewhat drier near sfc air allows for an improvement late
morning/aftn. KCMX/KSAW will improve to VFR with stronger drying,
while KIWD will improve to MVFR.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 333 PM EDT SAT APR 22 2017

WSW winds ahead of an approaching cold front as hi as 20-25 kts in
the area between Isle Royale and the Keweenaw will shift to the N up
to 20-25 kts tonight behind a cold front that will sweep across Lake
Superior. These steady N winds will diminish and tend to veer to the
ENE as a hi pres ridge builds over Lake Superior. Monday winds will
become easterly and increase to around 15 to 25 knots. Throughout
the day on Monday, winds will further increase to around 20 to 30
knots across much of the lake as an area of low pressure lifts out
of the central Plains. Monday night into Tuesday, winds will veer to
the southeast at 20 to 30 knots. Depending on the track of low
pressure, a few gale force gusts may be possible. During the day on
Tuesday as low pressure lifts across the area, winds of 15 to 25
knots are expected with south-southeast winds veering northwest.
Overnight Tuesday into Wednesday, winds will further veer
northeasterly and increase to 20 to 30 knots. Expect these winds to
continue Wednesday and the first half of Thursday as another system
develops in the Plains and lifts across the region.

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


LONG TERM...Ritzman
MARINE...KC/Ritzman is the U.S. government's official web portal to all federal, state and local government web resources and services.