526
FXUS63 KMQT 181833
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
133 PM EST Sat Jan 18 2025

.KEY MESSAGES...

- Lake effect snow and considerable blowing snow over the
  northwest wind snow belts into Sunday morning, especially
  east, where northwest winds gusting 25 to 35 mph will create
  occasional whiteouts from snow and blowing snow.

- Dangerously cold arctic air settles into the area this weekend
  into early next week, leading to temperatures remaining
  subzero from Saturday night through at least Tuesday morning
  over interior western Upper Michigan. Much of the rest of west
  and central Upper Michigan may see temperatures fail to rise
  above zero on Monday and maybe Tuesday.

- Homeowners and property managers should take action now for
  this cold period, especially if past very cold periods have
  yielded impacts. Ensure your Winter Car Survival Kit is up-to-
  date. This weekend through Tuesday, limit time outdoors for
  you and your pets, and check on vulnerable neighbors.

- Frequent whiteouts are expected in the northwest wind snow
  belts Saturday through Tuesday morning due to the falling snow
  being a fine, powdery type snow that is highly effective at
  reducing visibility. Expect very hazardous driving conditions in
  the lake effect snow areas.

- No widespread, significant snowfalls for Upper MI through next week.
  Nearly all of the snow that occurs will be lake effect driven.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 505 AM EST Sat Jan 18 2025

RAP analysis and water vapor imagery reveal a Clipper shortwave
moving through northern Ontario and the Upper Great Lakes early this
morning. The associated sfc low with this shortwave is analyzed near
James Bay with the cold front now moving through Lower Mi as it
already passed through the U.P. last evening. Strong cold advection
in the wake of the front has supporting sharply falling temperatures
early this morning and wind-parallel multi-band LES over the
northwest wind snow belts of Lake Superior.

Today into tonight, expect temperatures to continue to plummet today
into tonight as northwest winds usher in the coldest air of the
season. Arctic air flooding into the Upper Great Lakes region will
cause 850 temps to fall from the teens Celsius blo zero early this
morning to -23C east and -27C to -29C west by 12Z Sunday. The
increasingly colder air mass will become increasingly less efficient
for snow crystal growth due to the DGZ being squashed near the sfc
of the lake or eliminated altogether. This will result in plates or
columns for snow crystals instead of the fluffier dendrites. The end
result will be finer snow and less overall accumulation. Also very
dry air being advected across Lake Superior (dew points blo zero F)
will likely result in LES bands being spaced farther apart with time
and becoming increasingly less organized which will also limit LES
accumulation. On the flip side, the finer snow crystals (plates,
columns) will be more efficient at being lofted into the air by
winds, and thus reducing visibility in blowing snow. Expect whiteout
to near whiteout conditions in blowing snow under the LES bands
later today into tonight. Also, with the increasingly colder air
mass and enhanced lake-inducing troughing, expect areas of
increasing convergence as land breezes develop off Ontario and nw WI
and central Upper Mi. This increased convergence could offset the
poor snow growth to bring locally moderate snow into eastern Alger
and northern Luce County and perhaps the higher terrain of the west
from Twin Lakes through Rockland to north of Ironwood as well.
Overall, today through tonight, look for 2 to 5 inches of lake
effect snow accumulation for most of the northwest snow belt
locations, with the exception of possible 6-8 inch snow amounts for
the above mentioned enhanced convergence areas. Given the
expectation of higher LES accumulations and more impacts from
blowing snow with whiteout conditions decided to issue a Winter
Weather Advisory for Alger, northern Schoolcraft and Luce counties
into Sunday morning.

As for temperatures, high temps in the teens early today will fall
through the day into the single digits west and low teens east.
Temps will continue to plummet tonight with min temps around 0F east
to 5 to 15 below zero interior west half, coldest near the WI
border.

If venturing out this weekend be sure to dress warmly in layers and
keep a winter survival kit in your car in case of an emergency.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 500 AM EST Sat Jan 18 2025

By 12Z Sunday, the 500mb ridge over the Yukon will be at its peak
intensity, with ridging also building over Newfoundland and
Labrador. This will set up an extremely efficient surge of frigid
Arctic air in the form of an anomalously deep trough centered over
the Upper Great Lakes, with the GEFS showing a nearly -35 dam 500mb
height anomaly over the UP by 06Z Monday, good enough for below the
2.5th percentile of the NAEFS climatology. The HREF mean 850mb
temperature will be around the -30C mark Sunday (slightly warmer
values over the eastern UP, slightly cooler over western Lake
Superior). This will translate into surface high temperatures 50+%
likely to remain below 0F on Sunday. Similar high temperatures are
expected Monday and Tuesday as 850mb temperatures will not change
much according to the LREF mean. Low temperatures will take a
tumble, especially over the interior west, with the NBM calling for
-22F for the Tuesday morning and various MOS guidance calling for as
low as -28F near Watersmeet. The surrounding mornings will see lows
in the negative double digits in the interior west and negative
single digits elsewhere, still cold, but Tuesday morning will be the
coldest. With dominant surface pressure features far from the UP
(1040s mb low over the Plains, 960s mb low over Newfoundland and
Labrador), persistent WNW to NW winds gusting to around 20 mph are
expected. While those winds are not unusual for this time of year,
the combination with the frigid air temperatures will provide some
of the most hazardous wind chills since at least Feb. 2021, if not
Jan. 2019. At the LREF-mean wind chill of -44F in the Ironwood area
Tuesday morning, frostbite can take place in 10 minutes, half an
hour or less for much of the UP that is expected to see -20F or
lower wind chills through Wednesday morning. These have already
prompted Cold Weather Advisories to be issued and if the wind and
temperature forecast for Tuesday morning in particular continues to
gain confidence in such frigid wind chills, Extreme Cold Warnings
will be needed in future packages. Additionally, such cold air
moving over particularly shallow snowpacks (or in the case of the
southern UP, no snow pack) could drive a deep frost depth, which
would increase the threat of damage to pipes/etc that are not buried
particularly deeply, though frost depth forecasting is challenging,
so to what depth would be considered "safe" is uncertain.

Of course, with such frigid temperatures aloft and a wide-open Lake
Superior (only 3-4% ice cover per GLERL and most of it in Black Bay,
Nipigon Bay, the bays north of Sault Ste Marie, and the Apostle
Islands region), lake effect snow will be rampant. Such frigid
airmasses will support tiny crystals as the precipitating layer will
be well colder than the DGZ. QPF values are not expected to be
extreme with such a cold airmass not being able to hold much water
content, as the HREF only shows around 30% chances of 6-hourly QPF
rates above 0.2"/6hr in bands Munising and east and daily QPF of
0.15-0.4" on Sunday expected elsewhere in NW flow LES bands. This
broadly supports borderline Winter Weather Advisory impacts,
especially over the eastern UP, prompting an issuance this package.
Extensions in time and expansions to the west may become necessary
if a BLSN threat is realized with such a dry snow with tiny
particles that are extremely efficient at reducing visibility. The
Euro ensemble is calling for 50% probabilities of near-whiteout
conditions over the Keweenaw Peninsula Sunday with 80+% chance
of sub-quarter mile visibility through Monday and into Tuesday.

High pressure sliding to the south and east of the UP by Wednesday
will shift the boundary layer wind pattern to be more southwesterly,
providing a 1-2 combination of shifting lake effect bands offshore
and advecting warmer southern air over the UP, giving some reprieve
to the hazardous conditions ahead to end the weekend and begin the
work week. Granted, chances of high temperatures reaching the
"normal" mark (around 20) for this time of year are below 30% before
Friday, but after 48-72 hours of subzero temperatures, Wednesday`s
highs in the 11-16 degree range might just feel tropical. The GEFS
shows a small cluster of clipper low potential late Wednesday into
Thursday but uncertainty is high as any low feature would be running
face-first into high pressure residing over the eastern CONUS.
Regardless of exact solution, the LREF shows 925mb flow becoming 85%
likely to be within 30 degrees of NWerly by late Thursday into
Friday with greater than 75% chances of 850mb temperatures
supportive of an LES pattern, a return to cooler (but not frigid)
temperatures and LES is expected to end the work week. Moving into
next weekend, general troughing over the eastern CONUS with ridging
over the west is expected, but a progressive pattern is expected, so
despite the similarities in setup, a repeat of a semi long-duration
cold snap is not expected.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 133 PM EST Sat Jan 18 2025

General trend through the TAF period will be widespread MVFR
conditions at all TAF sites with periods of IFR/LIFR at IWD and CMX
in blowing snow/lake effect snow showers. Cannot rule out periods of
VLIFR conditions at times, either, in heaviest snow bands at CMX.
SAW, on the other hand, could start to trend toward VFR by this
evening. But, will keep a PROB30 to account for any isolated
visibility restrictions/snow squalls. Meanwhile, winds will remain
strong out of the northwest with gusts of 25 to 30 kts, highest at
CMX.

&&

.MARINE...
Issued at 500 AM EST Sat Jan 18 2025

Northwest gales to 35 knots are expected to become more isolated
throughout today into tonight with probabilities of gales
tonight only around 30% over Lake Superior. With large-scale
surface pressure features far away from Lake Superior, northwest
winds gusting to around 25 kt will be the norm through Tuesday.
Frigid arctic air will cause periods of heavy freezing spray
throughout the weekend and early portion of next week. High
pressure sliding to the south and east will cause winds to
become more southwesterly Wednesday, remaining around 25 kt,
though warming temperatures and a change in wind direction
reducing wave heights should reduce the freezing spray to light-
to-moderate. Beyond then, gales will depend on whether or not a
clipper low materializes in the mid-to-late week period, in
which case gales to 35 knots become possible in the late week
period, but probabilities at this time are only around 20-30%.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Cold Weather Advisory from 10 PM EST /9 PM CST/ this evening
     to 10 PM EST /9 PM CST/ Monday for MIZ001-003-009-010.

  Cold Weather Advisory from 10 PM EST /9 PM CST/ Sunday to 10
    PM EST /9 PM CST/ Monday for MIZ002-004>006-011>014-084-
     085.

  Winter Weather Advisory until 7 PM EST this evening for MIZ006-
     007-085.

  Winter Weather Advisory from 10 PM this evening to 1 PM EST
     Sunday for MIZ006-007-085.

Lake Superior...
  Heavy Freezing Spray Warning until 1 PM EST /noon CST/ Sunday
     for LSZ162-240>242-263.

  Heavy Freezing Spray Warning until 7 PM EST Monday for
     LSZ243>251-264>267.

  Gale Warning until 7 PM EST this evening for LSZ249>251-
     265>267.

Lake Michigan...
None.

&&

$$

SHORT TERM...Voss
LONG TERM...GS
AVIATION...TDUD
MARINE...GS