Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 232045

Area Forecast Discussion
National Weather Service Marquette MI
345 PM EST Thu Feb 23 2017

.SHORT TERM...(This evening through Friday)
Issued at 341 PM EST THU FEB 23 2017

The main forecast concern through Friday evening will be the arrival
of system snow across the area on Friday, with the potential for
upslope/lake enhancement snow in the northeast wind snow belts
Friday afternoon/evening. The initial system snow looks like it
will be on the wet and heavy side, especially across central and
eastern portions of the area. In the afternoon hours, the snow is
expected to transition over to a mixture of freezing drizzle/ice
pellets across the east.

Afternoon water vapor imagery shows a strong, deep upper-level
trough beginning to lift out of the southern Rockies with a
strengthening lee cyclone developing in far southwest
Kansas/southeast Colorado. Tonight, expect mid and upper level
clouds to stream back northward as the above mentioned system begins
to lift northeast towards the Great Lakes region. Do not expect any
precipitation tonight; however, through the early morning and
morning hours as surface to 850mb flow veers to the north-northeast
expect light lake effect snows to develop in the north and northeast
wind snow belts. 850mb temperatures do not look terribly cold and
the inversions are quite low, so not expecting much in the way of
lake effect accumulations across the north through the early morning
hours on Friday. However, further south across south central
portions of Upper Michigan were 850-700mb warm air advection begins
to lift north through the early morning hours, a fairly strong mid-
level front will strengthen and may allow for a quick 1 to 2 inches
of wet, heavy snow to fall through the early morning hours.

As we progress through the mid-late morning through the afternoon
hours, the models are fairly consistent with the warm air advection
wing to lift north across the area allowing system snow to spread
north across the remainder of Upper Michigan. Temperature profiles
are on the warmer side of things, especially across eastern and
central portions of the area, so the snow should keep wet and heavy
characteristics. As we progress through the afternoon hours, the
models are fairly consistent with a dry slot moving over at least
eastern portions of the area. Forecast soundings show cloud ice
dissipating within the dry slot; however, given the depth of the low-
level cold air would not be surprised the freezing drizzle is able
to refreeze before reaching the ground. Therefore, may see a mixture
of freezing drizzle/ice pellets. Further west across central and
western portions of the area through the afternoon hours, things
are a bit more uncertain. The GFS would favor a much drier
solution and would hold off additional precipitation chances until
the evening hours, but given the onshore flow and cooling 850mb
temperatures behind the system tend to favor the high-res models
guidance that favor higher QPF, especially across the higher
terrain in the northeast wind snow belts.

.LONG TERM...(Friday through Wednesday)
Issued at 603 AM EST THU FEB 23 2017

Positive height anomalies that have dominated the Great Lakes n thru
Hudson Bay in recent days, bringing unseasonable/record breaking
warmth to the area, have been shifting e and se over the last 24-
36hrs and will shift e more quickly this weekend. This will occur in
response to building heights over the ne Pacific/AK/nw Canada that
will support a trof shifting from the western CONUS to central N
America this weekend. These changes aloft will bring colder, more
typical late Feb conditions this weekend following a Plains to Great
Lakes winter storm that will lead the troffing into central N
America. Next week, 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 bitterly cold air, the coldest air in the northern
hemisphere, eventually developing across central/northern Canada.
With that large scale trof having varying amplitude into the CONUS
as shortwaves swing around it, temps next week may be quite variable
btwn blo and above normal across the Upper Lakes, though
normal/above normal may be the more common outcome on most days.
Whether or not the bitter cold air building to the n will be able to
make a surge to the s beyond next week remains to be seen, but right
now there are no strong signals for that to occur.

Beginning Fri, energy that is now over the western CONUS will have
shifted out into the central Plains by 12z and will close off a mid-
level low over IA during the day with associated sfc low tracking
toward northern IL/southern Lake MI. Overall thinking from yesterday
hasn`t changed too much as the mid-level low is still fcst to open
back up as it shifts across the western Great Lakes region Fri
night/Sat, though model trends indicate a slower opening up of the
low. This still suggests that the deformation hvy snow shield that
develops on the nw side of the system will peak to the sw of here
and then tend to weaken as it lifts into the Upper Lakes.

Waa/isentropic ascent will quickly translate ne thru the Upper Lakes
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. The
NAM, which had been a notable outlier in bringing a heavy swath of
pcpn s to n across the area Fri morning under a strong isentropic
ascent regime has pulled back and is now more inline with most other
guidance. This surge of pcpn will be all snow with all fcst
soundings across the area showing column temps blo 0C. With mixing
ratios around 3g/kg avbl in the 700-750mb layer, should see a
general 2-4in snowfall with this initial batch of snowfall on Fri.
Do have some concern across the s central/se fcst area where a
number of models show higher qpf under a bit more focused isentropic
ascent as well as some elevated instability which may yield some
convectively enhanced pcpn. Whether or not this occurs will be more
of a near term fcst problem as the event unfolds. Snowfall on Fri
will be wet/hvy making plowing/shoveling more difficult than normal.
The wet snow will also make roads especially slippery.

Fri aftn/night, there is uncertainty in whether sufficient mid level
drying will surge n into at least the eastern fcst area to cut off
ice nucleation as moisture above the sub -10C isotherm cuts out.
Local procedures suggest that will occur, but there are concerns
since not all models are aggressive with the drying. For now, fcst
reflects some mix with -fzra, more likely just -fzdz, which cuts
down snow accumulations over the e half to just 1-3 inches Fri
night. If the mid level moisture does not cut out, snow
accumulations will be higher than currently fcst Fri night. To the n
central and especially w, air mass will be more than cold enough to
support lake enhancement as winds back more directly onshore.
However, the w will be very near the edge of deep layer moisture,
making for a challenging fcst that could range from 6-12hrs of hvy
snow to just light snow. Fcst for the n central and w leans toward
the more conservative side with snow accumulations Fri night in the
3-6 inch range. System will exit on Sat with a transition to light
LES from w to e. Finally, gusty winds up to 30mph, higher at times
in exposed areas near Lake Superior, will lead to blsn, mainly Fri
night into Sat morning.

As it appears now, the potential for snowfall amounts to reach 12
or 24hr warning criteria is low and does not warrant the issuance
of a winter storm watch or warning.

The only other fcst item of note this morning occurs during the
midweek period next week. Shortwave dropping down the W Coast
Sun/Mon is fcst to shift e and ne to the Great Lakes midweek. GFS
still remains weaker with this wave, but is trending a little more
amplified. As has been the case over the last 24hrs, the
CMC/ECMWF remain more amplified and stronger with sfc low that
will lift into the Great Lakes, and suggest a low track far enough
n for mixed pcpn or even just rain for a time for at least parts
of the fcst area. Majority of CMC ensembles favor a warmer look,
and fcst will continue to include mixed pcpn. A few ensembles wrap
up a strong system, but the majority don`t. Will be a system to
monitor next week.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1221 PM EST THU FEB 23 2017

Expect conditions to improve through the afternoon hours with the
MVFR ceilings scattering out and leaving behind mid and upper-level
clouds tonight. With a storm system approaching from the south,
expect ceilings to drop back down into at least MVFR during the
early morning hours on Friday on onshore flow continues and cools
a bit. Expect lake effect snow showers to return across all
terminals with the lowering ceilings. As the system approaches
winds will veer around to the northeast at all terminals and
become gusty as well. Will allow subsequent TAFs to fine tune the
arrival of any lake enhanced/system snowfall for late tomorrow

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 522 AM EST THU FEB 23 2017

NE to N gales to 35-40 kts are expected over much of Lake Superior
Fri morning into Fri night. NW gale force gusts to 35 knots are then
possible over south central and eastern Lake Superior Sat into Sat
night. Some heavy freezing spray is possible Fri night into Sat
night, but coverage will be limited.

Upper Michigan...
Lake Superior...
  Gale Warning from noon Friday to 7 PM EST Saturday for

  Gale Warning from 7 AM EST /6 AM CST/ Friday to 1 AM EST
     /midnight CST/ Saturday for LSZ162-263.

Lake Michigan...
  Gale Warning from 7 AM to 7 PM EST Friday for LMZ248-250.



SHORT TERM...Ritzman
LONG TERM...Rolfson
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