Area Forecast Discussion
Issued by NWS Marquette, MI

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846
FXUS63 KMQT 130909
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
409 AM EST Wed Dec 13 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 337 PM EST TUE DEC 12 2017

WV imagery and RAP analysis indicated a mid/upper level trough over
the wrn CONUS and a trough from nrn Quebec into the Ohio Valley
resulting in nnw flow through the wrn Great Lakes. A vigorous
upstream shortwave trough was located over cntrl Alberta. Cold air
with 320-340 low level flow prevailed across Lake Superior producing
multiple wind parallel LES into the cwa. Radar indicated a steady
diminishing trend this afternoon with mainly just light and less
organized bands remaining. Winds were also weakening. So, the LES
headlines were cancelled. Radars also showed light snow advancing
through nrn MN in a strengthening WAA pattern.

Tonight, the remaining LES into the n cntrl cwa will continue to
diminish this evening as a weak sfc ridge moves in with diminishing
winds and inversion heights falling to 3k-4k ft. As the clipper
approaches and the sfc low and warm front move into MN the light
snow will increase over the sw with an around an inch possible
overnight. LES will also move offshore as winds become se.

Tuesday, the models have trended slightly farther north with the
path of the clipper and associated mid level fgen and isentropic
ascent over the region. Although moisture is modest with around 2
g/kg available, the dynamics should squeeze out a band of moderate
snow. With SLR values near 20, the system should bring snowfall
amounts of 1 to 3 inches near the WI border with higher amounts over
the far south toward Menominee where amounts up to 4 inches are
expected. In addition some ene to ne flow lake enhancement may add
to the totals at MNM. However, confidence in the
development/location of enhanced bands is low. Farther north, 850 mb
temps remaining around -16C with convergent ese flow will bring some
LES back into the Keweenaw and as winds back further in the
afternoon into nrn Marquette county, especially north of M-28.
Accumulations north of 1 to 3 inches will also be possible with some
locally higher amounts.

.LONG TERM...(Thursday through Tuesday)
Issued at 408 AM EST WED DEC 13 2017

Intermittent lake effect snow is expected through much of the
extended forecast with continued colder temperatures. The greatest
impact will likely be early in the extended late Thursday into
Friday evening as moderate to heavy lake effect snow is possible.

Thursday through 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 -16C and -22C, warmest Thursday into Thursday
evening. The colder temperatures will slide in aloft Friday and
Friday night as a reinforcing shot of colder air sinks southward
into the U.P. with another strong shortwave aloft. Initially winds
will be westerly across the U.P. Thursday and Thursday evening;
however, a surface low is expected to develop and intensify over
eastern Lake Superior as this wave digs into the area. This will
effectively shift the winds to the north 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 north to northwest wind favored snowbelts
Friday into Friday evening. Inversion heights are progged to jump to
around 10kft and 15kft as the wave slides overhead. Again, this
would point to a period of heavy lake effect snow late Thursday
night into Friday evening as deep layer moisture and forcing exist
through much of the sounding. Current thinking is that several
inches of lake effect snow may fall from portions of the north-
central 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 are possible
Friday into Friday evening across the eastern half of the U.P.
downwind of Lake Superior.

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 lake effect 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 reinforced over the eastern
CONUS generally allowing for northwest flow aloft as a broad ridge
continues over the western CONUS. This will lead to intermittent
lake effect snow chances through much of this period 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.
&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1222 AM EST WED DEC 13 2017

MVFR ceilings continue to spread east across the area as snow ahead
of approaching clipper system moves in. IFR visibilities expected
at all three sites as the snow intensifies overnight and early
Wednesday, but conditions to remain IFR at KIWD through the
afternoon and evening while KSAW and KCMX will see MVFR conditions
return late in the forecast as snow ends there.
&&

.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 from 11 AM this morning to 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...JLB
LONG TERM...KEC
AVIATION...RJT
MARINE...KEC



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