Avalanche Forecast

Issued: Nov 25th, 2021 4:00PM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Wind Slabs.

Avalanche Canada cgarritty, Avalanche Canada

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Be ready to manage reactive wind slabs if you ascend high enough to find dry new snow accumulations. Danger will be low where Thursday's rain set up a new crust on the surface.

Summary

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Thursday night: Continuing wet snow/rain bringing 10-20 cm of new snow to the alpine, possibly treeline. Moderate to strong southwest winds.

Friday: A mix of sun and cloud with the most clearing in the evening. Light west winds. Treeline high temperatures around -1 with freezing levels returning to about 1200 metres.

Saturday: Cloudy with snowfall quickly switching to heavy rain; 30-40 mm, increasing overnight. Light to moderate southeast winds, increasing overnight. Treeline high temperatures around +4 with freezing levels rising to 2800 metres.

Sunday: Diminishing rain switching to light flurries bringing up to 10 cm of new snow. Light to moderate southwest winds. Treeline temperatures dropping from +4 to +1 over the day.

Avalanche Summary

No avalanches have been reported in the region. After Thursday's rain, avalanche potential is expected to be limited to the highest alpine areas in the region. Depending on where our snowline ended up during the storm, quite large windslabs may now be perched and primed for human triggering on leeward terrain features in the alpine. Step up your caution several notches if you begin to encounter dry snow accumulations on your ascent.

Reports in the region remain limited. Be sure to post your observations to the Mountain Information Network!

Snowpack Summary

By the end of Thursday's storm, the region will have picked up 70-90 mm of precipitation, however much of this will have fallen as rain. High alpine locations in the region could have accumulated as much as 70 cm of new snow during this event, but there is a lot of uncertainty about this. 

Where dry snow fails to accumulate, the snow surface should become capped by a solid crust as cooling occurs Friday night. At that point this surface crust may effectively combine with another crust that was only 10 cm deep when the storm began. Another rain crust exists near the bottom of the snowpack. 

Average alpine snow depths in advance of the storm were around 100-120 cm and we have yet to see how much the storm added. Snowpack depth tapers dramatically with elevation at treeline and below. Much of treeline and all below treeline elevations remain below threshold depths for avalanches.

Early season hazards such as rocks, stumps, and creeks are a concern below the alpine.

Terrain and Travel

  • Closely monitor how the new snow is bonding to the old surface.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Wind Slabs

An icon showing Wind Slabs

Expect to find new wind slabs - possibly still reactive to human triggering on Friday - in areas where dry snow has accumulated. High elevations and pockets to the immediate lee of ridges and exposed terrain features are where you'd find this problem.

Aspects: North, North East, East, South East, West, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Nov 26th, 2021 4:00PM