Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 150426
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1126 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 night through Thursday)
Issued at 313 PM EST THU DEC 14 2017

Friday night and Saturday: Lake effect snow in the NW wind snow
belts will be ongoing Friday evening, especially across the west
half of Alger County. A surface pressure saddle point will then
shift southeastward across the CWA Friday night, allowing the
surface winds to gradually veer through the night. Though inversion
heights will lower to about 3kft, ideal snow growth conditions in
the remaining convective layer combined with light winds and upslope
effects should result in a period of low-QPF/high-SLR snow for far
western Alger County and much of Marquette County along Lake
Superior. The thermodynamic set-up with light winds supports SLRs of
at least 30:1 and possibly higher than 40:1. Given the light wind
field and the high SLRs, it is possible a couple meso-lows could
produce high snowfall rates over a 1-2hr period. Given the time of
day/week, overall impacts should be relatively minor. The light,
high SLR LES will then shift to the north half of the Keweenaw on
Saturday as 850hPa temps remain as low as -14C.

Very light snow of a up to a few tenths of an inch forced by WAA may
occur along the SW CWA on Saturday, but again, overall impacts
should be fairly minor.

Sunday and Monday: Somewhat zonal flow along with weak surface
ridging and increasing 850hPa temps will allow for mostly dry
conditions and moderating temps during this time.

Tuesday through Thursday: Another shot of colder air associated with
an ESE-ward advancing mid-level trough will usher in more LES for
the W to NW wind snow belts Tuesday into Wednesday, and the N to NE
wind belts on Thursday. Gusty west winds, especially across the
Keweenaw, will be possible Tuesday into Tuesday night as a notable
isallobaric wind component crosses the CWA behind the trough.
&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1125 PM EST THU DEC 14 2017

Lake effect snow showers will continue allowing ceilings and
visibilities to drop at KCMX/KIWD. Could see LIFR conditions at
times during heavier snow showers overnight. Expect IFR conditions
later tonight into the afternoon at both sites as snow showers
continue. KSAW will have light snow 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
there.
&&

.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 until midnight EST Friday night for
     MIZ006-007-085.

  Winter Weather Advisory until 4 PM EST /3 PM CST/ Friday for
     MIZ001>004-009-084.

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

$$

SHORT TERM...JLA
LONG TERM...Kluber
AVIATION...07
MARINE...BB



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