Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 132005
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
305 PM EST Wed Dec 13 2017

.SHORT TERM...(Today and tonight)
Issued at 439 AM EST WED DEC 13 2017

...Slippery Morning and Evening Commutes Expected Across Portions of
Upper Michigan Today...

A clipper system is currently tracking across the Upper Mississippi
Valley as multiple shortwaves evident on water vapor imagery
continue to dig southeast towards the region. 850mb winds have back
to the south-southeast this morning, which allowed lingering lake
effect snow east of Marquette to push offshore this morning. Across
the west, light snow was observed; however, a more robust band of
snow has developed across central Minnesota and northwest
Wisconsin, which will be the main forecast concern for the day.

Today: The main concern is the strong fgen band expected to track
along the Wisconsin/Michigan border through the day today as the
main clipper system tracks across southern Wisconsin this afternoon.
This band is expected to track west to east across western and
central Upper Michigan this morning and will impact the morning
commute. As strong isentropic lift develops along this band of
frontogenesis, expect fairly deep lift to develop and allow for snow
to fall moderate, to even heavy, at times. Forecast soundings show
this deep lift with a fairly deep residence time for hydrometeors
through the DGZ. Therefore, expect this system snow to be rather
efficient. However, with the thermal profile anchored more towards
the -10C isotherm, SLRs should be lower than 20:1, and will make for
a wetter, more sloppy snow. The track of the surface and 850mb low
coupled with 850mb temperatures around -15C, we`re also looking at a
good setup for lake enhanced snow across the south central. This
will lead to localized amounts a bit higher on the west side of the
Bay of Green Bay. The system snow will come to an end across the
west this afternoon, but may linger into the evening hours across
the south central. Across the Keweenaw and eventually north central
Upper Michigan as the 850mb flow comes around to the east and then
northeast later this morning and afternoon, respectively, and
remains between -15 and -18C expect lake enhanced snow to impact
those locations. Across the north central, this lake enhanced snow
will transition over to lake effect by this evening. Did expand the
winter weather advisories and issued an SPS to account for the
impacts expected during the morning and evening commutes.

Tonight: As the clipper system continues to track southeast across
the lower Great Lakes cold air advection will ramp up across the
Upper Great Lakes and allow for lake effect snow to return, if not
already ongoing from this afternoon. As a few weak shortwaves dig
across the region overnight, this will back the 850mb flow and push
the resulting lake effect snow from northeast to northwest snow
belts. With 850mb temperatures progged to remain around -18C over
night, expect lift through the DGZ to be strong enough to support
additional snowfall accumulations, possibly upwards of 3 inches in
some spots.

.LONG TERM...(Thursday night through Wednesday)
Issued at 303 PM EST WED DEC 13 2017

...Lake effect Thu night into Fri then warmer late this weekend into
early next week...

Upper troughing and cold continues into first part of weekend. Could
be brief relaxing of upper trough to more of a WNW flow aloft late
this weekend into early next week which may allow us to see temps
push above normal into the lower 30s on Sun-Tue. Primary long range
models (GFS, ECMWF, GEM) along with associated ensembles and recent
runs of longer range CFS indicate any warm up will be brief with
persistent pushes of cold air dropping through again later next week
and on into the rest of the month. Signal continues that it could
get very cold (sub zero lows and single digit highs) just beyond the
end of the long term toward the holiday weekend. We`ll have to wait
and see on that though.

Main weather issue for the long term is bout of moderate to heavy
lake enhanced snow expected Thu night into Fri for the northwest
wind snow belts near Lk Superior. Strong shortwave trough digs down
across Lk Superior and Upper Michigan late Thu evening through early
Fri morning. Similar to recent trends it seems, could see light snow
arriving just in time for Fri morning commute away from the lake
effect areas. Additional shortwave energy drops across Fri morning
through late Fri afternoon but moisture with that wave is less than
the earlier morning wave so probably will not see much widespread
light snow but could see some more flurries. Lake induced troughing
helps low pressure over far eastern Lk Superior deepen from 1013mb
late Thu night to around 1008mb Fri morning. Subtle deepening of the
low, but this will only increase low-level convergence with the lake
effect.

Soundings over west and northwest show lake induced troughing to at
least 10kft AGL with strong lift well within DGZ. Winds in blyr less
than 20 kts into Fri should allow snow to be quite efficient with
SLRs 25-30:1 at least. Winds do look to shift some from W to NNW and
back to NW as the shortwaves move through. Overall, expect moderate
to heavy lake enhanced snow over west and northwest Thu night into
Fri morning. Meanwhile, over the east the low and sfc trough could
disrupt the lake effect over the east with main area of heavier lake
effect possibly shifting out over Lk Superior late Thu night or more
so Fri morning depending on where main center of low ends up. 12z
GEM shows such a scenario while most other higher res guidance still
keeps heavier snow showers in over northeast forecast area. Will
need headlines for this event. At this point, winds and blowing snow
does not look to be big factor. Snow could be very fluffy though so
should see solid advisory but if snow showers can stay anchored
later Thu night into Fri morning certainly a potential for isold
warning amounts of 8"/12 hours. Too much uncertainty where focus for
heavier snow will be to go with a winter storm watch for lake effect
attm, especially since the wind/blowing snow should not be too big
of an issue.

Beyond the lake effect late this week, weekend looks pretty quiet
other than some snow that develops as warmer air works in. Stronger
upper level waves that could focus stronger low pressure systems
remains well to south as it looks now, so think we will be okay in
terms of staying away from stronger low pressure/widespread heavy
snow that can sometimes come with switch from colder pattern to
warmer one. Cold front charging in Tue/Wed of next week will
bring next better chance of widespread snow with more lake effect
by Wed as colder air returns.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 108 PM EST WED DEC 13 2017

Light to moderate widespread snow will end this afternoon as the
supporting low pressure system slides to the southeast. So, some
improvement to MVFR is expected. However, winds will become
northeasterly throughout the day today, allowing upslope flow and
additional snow showers across KSAW and KCMX through the end of
the day. Tonight, as winds back to nrly, lake effect snow showers
will return to all terminals at times with MVFR ceilings and
variable reduced visibilities.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 408 AM EST WED DEC 13 2017

Winds will remain at or below 25 knots through Thursday night as the
pressure gradient relaxes across Lake Superior. Winds will increase
to 20 to 30 knots late Thursday night through Friday evening as the
next low pressure system develops and strengthens over eastern Lake
Superior. Winds will then remain in the 15 to 25 knots range through
the beginning of the work week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 1 AM EST Thursday for MIZ005.

  Winter Weather Advisory until 7 PM EST /6 PM CST/ this evening
     for MIZ010>013.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Ritzman
LONG TERM...JLA
AVIATION...JLB
MARINE...KEC



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