Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 140909
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
409 AM EST Thu Dec 14 2017

.SHORT TERM...(This evening through Thursday)
Issued at 427 PM EST WED DEC 13 2017

WV imagery and RAP analysis indicated a mid/upper level ridge over
wrn North America and a trough from north of Hudson Bay through the
ern CONUS. A vigorous shortwave torugh that has produced a swath of
moderate to heavy snow from nrn WI into srn upper MI, extended from
se WI into wrn IN. At the surface, a 992mb low was located over srn
Lake Michigan resulting in cyclconic ene to ne flow across the cwa.
Lake enhanced snow (850 mb temps near -17C) into n cntrl Upper
Michigan was transitioning to LES with an area of moderate to heavy
snow.

Tonight: Expect the clipper system snow to slowly taper off into
this evening, per usptream obs over most of nrn WI with lingering 1-
2sm vsby. With amounts up to 8 inches already observed near
Menominee to Stephenson, the winter weather advisory was upgraded to
warning given potential for a few more inches, including some lake
enhancement. In addition to the snow, considerable blowing and
drifting snow will lead to to very poor driving conditions during
the evening commute.

Expect the initial burst of heavier snow around KMQT to also give
way to weaker multiple parallel band LES as subsidence moves in
and the 850-700 mb moisture moves out of the area with weakening
low level convergence. In addition, winds will also steadily back
to nrly this evening and to the nw overnight, shifting the focus
of any heavier bands.

Thursday, As another shrtwv drop toward the area out of Manitoba,
winds will continue to back from nnw to wnw. Even with 850 mb temps
remaining near -17C, inversion heights at or falling below 5k ft
will limite LES intensity. Only 1 to 3 inch amounts are expected for
nw flow favored areas with the greatest amounts from Munising
eastward.

.LONG TERM...(Friday through Wednesday)
Issued at 407 AM EST THU DEC 14 2017

Intermittent lake effect snow is expected through much of the
extended forecast with continued colder temperatures; however, there
will be some slight moderation in temps this weekend before colder
air moves in again. The greatest impact will likely be early in the
extended Friday into Friday evening as moderate to heavy lake effect
snow is possible for northwest wind snow belts.

Friday and Friday night: The deep troughing over the eastern CONUS
is expected to linger through this time period allowing below normal
temperatures to remain in place. 850mb temperatures are progged to
be between -18C and -22C Friday through this time period. Colder
temperatures will slide in at the surface as a reinforcing shot of
colder air sinks southward into the U.P. with another potent
shortwave aloft. A surface low is expected to develop and intensify
over eastern Lake Superior as this wave digs into the area and
heating from the lake helps to deepen the low. This will effectively
allow winds to become north-northwest to northwest across much of
the area, especially over the eastern half of the U.P. This would
allow for favorable conditions for a period of moderate to heavy
lake effect snow for the aforementioned snowbelts Friday into Friday
evening. Inversion heights are progged to jump to around 10kft to
13kft as the wave slides overhead. Again, this would point to a
period of heavy lake effect snow during this time period as deep
layer moisture and forcing exist through much of the sounding and
most notably the DGZ. Current thinking is that several inches of
lake effect snow will fall from portions of the northwest U.P. and
especially through the eastern U.P. along Lake Superior. Models are
fairly similar in pegging those areas for the heavier snow; however,
a slight change in wind direction will shift the favored snow bands.
Stay tuned for updates for this time period, but it does appear that
headline worthy snowfall totals can be expected Friday into Friday
evening across the eastern half of the U.P. downwind of Lake
Superior. Issued a winter weather advisory for the western U.P.
through Friday afternoon; however, as the trough shifts east, the
snow should begin to taper off by late Friday afternoon over the
west. The eastern U.P. will likely need at least an advisory
through Friday morning through Friday night, while the north-
central U.P. may also need an advisory through Friday afteroon
into possibly Saturday morning as winds become more north to
northeasterly.

Saturday into Sunday: A weak low pressure system is expected to
slide to the south of the U.P. as yet another upper-level
disturbance slides across the Upper Great Lakes.  This will provide
just enough moisture and lift to provide very light snow or possibly
flurries across the U.P. 850mb temperatures moderate significantly
with much of the area seeing 850mb temps in the -6C to
-8C range.  This will minimize any lake enhancement for this time
period. Surface temperatures will warm as well with most locations
seeing highs in the mid to upper 20s by Sunday.

Rest of the extended: Broad troughing is expected to be reinforced
over the eastern CONUS by Wednesday allowing for northwest flow
aloft as a broad ridge builds over the western CONUS. This will lead
to intermittent lake effect snow chances picking up once again
Wednesday through the rest of the extended with the favored bands
depending largely on the low to mid level flow. Models differ on
timing of the better shortwave enhancements during this time period,
which is typical for the end of the extended forecast; therefore,
will stick with a consensus of the models with the intermittent lake
effect snow chances, mainly downwind of Lake Superior. There is a
hint of a stronger low pressure system pushing into the area next
Thursday into Friday; however, models are having trouble with time
and placement. Again, will stick with consensus for this time period
with the introduction of pops next Thursday.
&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1138 PM EST WED DEC 13 2017

Lake effect snow showers will continue at all terminals at times
with MVFR ceilings and variable reduced visibilities. Lake effect
snow showers will end by afternoon at KSAW.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 427 PM 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 from 10 PM this evening to 4 PM EST
     Friday for MIZ001-003-004-084.

  Winter Weather Advisory from 5 PM EST /4 PM CST/ this afternoon
     to 4 PM EST /3 PM CST/ Friday for MIZ002-009.

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

$$

SHORT TERM...JLB
LONG TERM...KEC
AVIATION...07
MARINE...JLB



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