Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 142002
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
302 PM EST Thu Dec 14 2017

.SHORT TERM...(This evening through Friday)
Issued at 253 PM EST THU DEC 14 2017

...Lake effect ramps up again this evening with moderate to heavy
accumulations expected into Friday...

Northwest flow aloft persists between strong ridge over western
Conus and deep trough in eastern Canada. Stronger shortwave evident
in wv loop over northern Manitoba to northern Ontario. This wave
drops across Upper Great Lakes tonight into Friday morning helping
to sharpen up sfc trough currently along the south shore of Lk
Superior. These larger scale features combined with sufficient over
water instability with delta t/s 18-20c tonight will result in lake
enhanced snow. Initial area for stronger lake enhanced snow
develops late this aftn into the evening vcnty of Porcupine
Mountains to the higher terrain just south of Houghton. At least
that is what most recent high res guidance, including the
HRRR/NAM/WRFs, show which makes sense based on current wind fields
across Lk Superior and western U.P. Should also see stronger
dominant band of snow develop this evening over far northeast
area near Lk Superior, vcnty of Grand Marais and Deer Park.

As shortwave works through tonight, expect low pressure to form
along the trough over eastern Lk Superior after midnight. Result
will be winds turning northwest over western U.P. which will spread
snow showers farther inland. Forecast soundings as all this occurs
shows lake equilibrium levels up to around 10kft AGL. Given depth of
convective layer and stronger lift within DGZ, should see moderate
to at times heavy snow (SLRs 25-30:1) with greatest focus overnight
for the higher terrain north and east of Ironwood and Porcupine
Mountains to Rockland/Mass City and to Twin Lakes. Northwest flow
also favors higher terrain of Baraga county vcnty of Alberta and
Herman for heavier snow overnight. Tweaked timing for a bit
earlier start time for Keweenaw to Baraga county winter weather
advisory, but overall kept previous timing for advisory into
Friday over the west and northwest for the moderate to heavy snow.

Over the east, expect strong band of snow that develops vcnty of
Grand Marais to remain stationary overnight before pushing onshore
late tonight or Fri morning. This continues to be potential
problem point of the forecast though as some models indicate with
sfc low over eastern Lk Superior and land breeze enhanced
southwest sfc flow, that the heavier snow band may lift back over
Lk Superior before shifting back onshore Fri morning with possibly
some embedded mesolows within the overall trough. Once the band
and various mesoscale features moves onshore, regime will
gradually transition to more of a northwest flow multiband setup
rest of Fri into Fri evening. Lake induced equilibrium levels up
to 10-12kft AGL favor heavier snow at times, though h85 temps only
around -13c to -15c will cut down on the over-water instability
slightly. Overall looks like solid advisory event with isolated
near warning amounts (most probable near Grand Marais), highly
dependent whether stronger band of snow late tonight stays onshore
and/or if mesolow enhanced snows persist for any appreciable time.
This will be a nowcast type of scenario to pin down. Strong winds
and blowing snow limited with the snow tonight into Friday so
that should lessen the impact to vsby outside of heavier snow
bands.

Away from the lake effect, could see some light snow or flurries
late tonight into Fri morning as the upper level shortwave moves
through. In general the lift with the wave looks weak so snow
amounts inland should be less than a half inch for most areas.

.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 afternoon
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 18Z TAFS through 18Z Friday afternoon)
Issued at 1246 PM EST THU DEC 14 2017

Light lake effect will keep ceilings around the MVFR range this
afternoon across the western terminals. Later this afternoon through
the overnight hours expect this lake effect to intensify allowing
ceilings and visibilities to drop at KCMX/KIWD. Could see LIFR
conditions at times during heavier snow showers mid evening through
the overnight hours. Expect IFR conditions later tonight through end
of period at both sites as snow showers continue. KSAW will mainly
VFR conditions into this evening before light snow moves back in
which will result in mainly IFR vsby and MVFR cigs. Conditions will
improve on Fri morning as northwest winds keep most of the lake
effect snow showers away from the terminal.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 253 PM EST THU DEC 14 2017

Winds will stay generally below 20 knots through the weekend except
for a few northwesterly gusts to 25 knots late Friday night and into
Saturday. Southwesterly winds will increase late Monday to 20 to 30
knots before veering to northwesterly gales to 35 knots Tuesday
evening. With increasing wave heights, freezing spray is possible
late Tuesday night and into Wednesday. Winds will then remain
between 20 to 30 knots Wednesday especially across the eastern half
of Lake Superior before weakening wednesday night.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory from 10 PM this evening to midnight EST
     Friday night for MIZ006-007-085.

  Winter Weather Advisory from 7 PM this evening to 4 PM EST
     Friday for MIZ001-003-004-084.

  Winter Weather Advisory until 4 PM EST /3 PM CST/ Friday for
     MIZ002-009.

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

$$

SHORT TERM...JLA
LONG TERM...KEC
AVIATION...JLA
MARINE...BB



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