Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221247
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
747 AM EST Wed Feb 22 2017

.SHORT TERM...(Today and tonight)
Issued at 456 AM EST WED FEB 22 2017

Scattered showers have resulted from a weak shortwave currently over
the CWA. These showers will exit E over the next few hours.

Short term is quite challenging due to unknown location and strength
of mesoscale banding associated with an incoming shortwave and
associated SFC low. All models generate bands of precip starting
either late this morning or this afternoon, which should be all or
mostly rain into the evening, but will begin to mix with snow from
NW to SE late this evening into tonight. Drizzle/freezing drizzle is
then expected tonight in N wind favored upslope areas late tonight,
but do not expect ice accumulations to be significant. Snowfall of
up to 1-2" over the higher terrain NW is possible. There is
potential for greater QPF amounts today/tonight, but wanted to stick
away from the outlier models given lack of certainty. Lows tonight
will range from the upper 20s to the mid 30s.

.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 enhancment 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 12Z TAFS through 12Z Thursday morning)
Issued at 746 AM EST WED FEB 22 2017

An area of rain will move into all sites today, transitioning to
snow this evening then possibly to freezing drizzle late tonight.
Expect ceilings and vis to lower as well. There is uncertainty as to
where the heaviest precip will develop, so expect changes in future
update.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 456 AM EST WED FEB 22 2017

A low pressure system moving through the region is expected to bring
NE gales of 35-40kts over western and north-central Lake Superior
late Thu night into early Fri night. N-NW gale gusts to 35 knots are
then possible over south-central Lake Superior Sat. Some heavy
freezing spray is possible Friday night into Saturday night.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Titus
LONG TERM...Rolfson
AVIATION...Titus
MARINE...Titus


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