Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221946

Area Forecast Discussion
National Weather Service Marquette MI
246 PM EST Wed Feb 22 2017

.SHORT TERM...(This evening through Thursday)
Issued at 245 PM EST WED FEB 22 2017

A mid-level front lifting through northwest Wisconsin into Upper
Michigan has allowed a narrow band of light rain develop this
afternoon. Further upstream across the northern plains, a shortwave
continues to rotate towards the Upper Great Lakes Region, with cold
air filtering southward from Canada.

It has taken the low-levels a bit to moisten this afternoon, but
expect this light rain to continue to lift northeast across the area
as the mid-level front traverses Upper Michigan. Given the
convective nature of the mid-level front, a few locations across
western and north central portions of Upper Michigan could see a
brief period of moderate rainfall through the evening. However, with
the band quickly lifting northeast, the better mesoscale lift will
be displaced northeast of the area. The attention then turns to the
above mentioned shortwave that will lift across the area tonight
bringing another chance for precipitation. As the main vort-max
arrives and colder air begins to filter southward, expect rain to
transition over to snow across the west and portions of the central
Upper Michigan. Thermal profiles do not look terribly impressive, so
do not expect SLRs to be high. Therefore, even though snow will
finally return to the area do not expect much in the way of
accumulations. Locations right along the lake shore and across the
higher terrain will have the best chances at seeing any accumulating
snowfall with north to northwest onshore flow.

Thursday morning, as the deeper moisture vacations the region
soundings show the potential for lingering precipitation, primarily
across the north wind snow belts. The question will be if cloud top
temperatures will be cold enough to support the production of ice.
With the 850mb temperatures only progged to drop to around -6 to -
8C, could see a mixture of light snow and freezing drizzle in the
north wind snow belts. Across the east, temperatures look like they
will be just warm enough to support drizzle, versus freezing
drizzle. Expect precipitation across the area to diminish through
the late morning hours, but cloud cover will linger across much of
the area. With the colder air dropping down from Canada, expect
temperatures to become more seasonable during the day on Thursday,
while still remaining 5 to 10 degrees above normal.

.LONG TERM...(Thursday through Tuesday)
Issued at 445 AM EST WED FEB 22 2017

Positive height anomaly that has dominated the Great Lakes n thru
Hudson Bay for the last several days, bringing unseasonable/record
breaking warmth to the area, will shift slightly e over the next few
days before shifting e more quickly this weekend. This will occur in
response to building heights over the ne Pacific/AK vcnty that will
support a trof over the western CONUS which will translate to
central N America this weekend. These changes aloft will spell an
end to the unseasonable warmth across the area as colder, more
typical late Feb conditions set in this weekend following a Plains
to Great Lakes winter storm that will lead the troffing into central
N America. Next week, it appears that the positive height anomaly
over the ne Pacific will retrograde a bit, and broad troffing will
set up across much of Canada. This will allow a good supply of
arctic air to build up to the n with the coldest air in the northern
hemisphere eventually developing across northern Canada. With
shortwaves tending to drop down the W coast and then swing e, temps
will likely be more variable btwn blo and above normal across the
Upper Lakes next week. The variation in temps will depend on depth
of shortwaves dropping down the W Coast and the magnitude of forced
building of heights downstream toward the E Coast as the trofs head
e or ne. This type of pattern, which may persist for a couple of
weeks, could certainly be an active one for the Upper Lakes.

Beginning Thu, rather vigorous shortwave tracking across the Upper
Lakes tonight will be just e of the fcst area by 12z Thu. In the
wake of the wave, shallow moisture not extending to the -10C
isotherm and upslope northerly wind could yield some -dz/-fzdz in
the morning near Lake Superior. Otherwise, expect a partly to mostly
cloudy, cooler day with highs in the 30s n to lwr 40s s central.

Attention then turns to shortwave energy moving across the western
CONUS tonight. This energy is fcst to close off a mid level low over
the central Plains by Fri morning before opening back up as it
shifts across the western Great Lakes region Fri night/Sat. The
deformation hvy snow shield that develops on the nw side of the
system will peak across the Plains soon after the mid level low
closes off. If the trend to then open up the mid level low is
correct, that will be key to snowfall here as it will signal a
decaying trend to the deformation hvy snow shield as it lifts into
the Upper Lakes. It appears the proximity of the mid level low over
Manitoba is an important factor in causing this system to
open/weaken as it lifts into a more confluent flow btwn that feature
and the downstream ridge.

Waa/isentropic ascent will quickly translate ne thru the Upper Lakes
late Thu night/Fri morning downstream of the deepening system over
the Plains. Additional forcing will be provided by the right
entrance of a 100kt upper jet lifting n across the Upper Lakes to
northern Ontario. NAM is an outlier, being deeper and a little
farther ne with the mid level low over the central Plains at 12z
Fri, which explains the much stronger push of isentropic ascent and
thus heavier pcpn moving across Upper MI very late Thu night and Fri
morning. Have favored the consensus of the other models in showing a
less aggressive push of isentropic ascent into Upper MI. This surge
of pcpn will be all snow. With mixing ratios around 3g/kg avbl in
the 700-750mb layer, could see a general 2-4in snowfall with this
initial batch of snowfall thru early Fri aftn. There are fairly
strong indications that mid level dry air may push into roughly the
e half of the fcst area later Fri into Fri night which would result
in a transition toward mainly -fzdz/-dz at times until a change back
to just snow by Sat morning. Meanwhile, diminishing deformation snow
shield will streak up thru the w half of the fcst area. At some
point, ne veering to nw winds and cooling column will support
development of lake enhancement off Lake Superior, and this will be
the biggest factor for boosting snow totals later Fri into early
Sat. Unfortunately, there is decent uncertainty in how much overlap
there will be between favorably cold column for lake enhancement
and deep layer synoptic forcing before it pulls out. Right now,
window looks fairly short. In the end, with snow accumulations
drawn out over a longer time rather than compressed into 12 or
24hrs, situation is marginal for reaching 12 or 24hr warning
criteria snow amounts. Thus, winter storm watch headlines are not
warranted with this fcst issuance. Snow will be on the wet/hvy
side, so plowing/shoveling will be more difficult. The wet snow
will make travel conditions more difficult as well. Finally, gusty
winds will lead to some blsn, especially in open areas more
exposed to Lake Superior.

Transition to diminishing LES off Lake Superior will occur during
Sat. Some light LES may continue thru Sun/Mon.

Heading into the midweek period, attention turns to the next
shortwave dropping down the W Coast Sun/Mon. Until recently, the GFS
was using this energy to wrap up a significant storm system that
would track ne into the Great Lakes region. Recent runs have trended
flatter and more positively tilted with the trof, and thus weaker
with sfc low reflection and pcpn. On the other hand, CMC/ECMWF runs
which used to look like recent GFS solutions have been trending
stronger. In fact, so much so that the sfc low takes a track far
enough nw to result in more of a mixed pcpn event or even just rain
for at least parts of the fcst area. GFS ensembles mostly support
the operational solution. The CMC ensembles show more spread in
strength, but a number do suggest a warmer solution that would lead
to mixed ptypes. Fcst for now will reflect an averaging of
solutions, yielding at least some mixed pcpn developing Tue.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1254 PM EST WED FEB 22 2017

A fairly narrow band of rain has developed along a mid-level front
across northwest Wisconsin. This band will continue to lift
northeast through the afternoon and evening hours impacting KIWD
first and then KCMX/KSAW bringing reduced visibilities, lowering
ceilings, and light rain. Depending on where the band sets up,
visibilities could drop a little lower than MVFR or be just above
MVFR. Later this evening, as a shortwave moves across the area,
additional lift will push through the area and impact all
terminals. This additional lift will also come with a cold surge,
and allow rain to transition over to snow this evening/tonight.
Towards the morning hours as the deeper lift vacations the region,
depending on how cold cloud top temperatures can stay, could see
some freezing drizzle mix in with the snow.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 245 PM EST WED FEB 22 2017

Tonight into Thursday morning as low pressure lifts out of central
Wisconsin across lower Michigan, the surface pressure gradient will
increase, along with subsidence, resulting in increased northerly
winds of 20 to 30 knots. Late on Thursday, expect the winds to
decrease in speed to around 15 to 20 knots. Thursday into Friday as
a storm system begins to organize across the Central Plains, flow
will become northeasterly and begin to increase to around to 20 to
30 knots, especially across western portions of the lake. As the
system gets closer during the day on Friday, expect northeast gales
of 35 to 40 knots to develop. As the system moves just to our south,
expect northeast winds to back to the north with gale force gusts
still possible Friday night into Saturday. Through much of the
weekend expect north winds 20 to 30 knots. By Sunday afternoon the
winds will begin to weaken to around 15 to 25 knots as the winds
back westerly. Monday through Tuesday, winds will become southerly
at around 20 knots.

Upper Michigan...
Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 10 PM EST this evening for LMZ248-250.



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