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Avalanche Forecast

Archived

Apr 21st, 2024–Apr 22nd, 2024

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.

Regions

Haines Pass.

Large persistent slab avalanches may remain possible to human trigger in the alpine.

Avoid steep or convex slopes where triggering slabs is more likely.

Confidence

Moderate

Avalanche Summary

Numerous recent wet loose and slab avalanches up to size 2.5 were reported on a variety of aspects in the alpine on Saturday.

The slab avalanches likely failed on either a crust or a weak layer of surface hoar, depending on the aspect of the slope. Strong solar radiation often increases the likelihood of triggering both loose and slab avalanches. See MIN 1 and 2.

Snowpack Summary

A mix of wind affected and soft snow can be found in the alpine. Sunny aspects have a crust on the surface that may soften with daytime heating.

A few large slab avalanches were recently reported on a variety of aspects on steep alpine slopes. They likely failed on either a crust or a weak layer of surface hoar down 30 to 70 cm.

Cornices are large and looming at this time of year.

Weather Summary

Sunday night

Mostly cloudy with isolated flurries, 0 to 5 cm snow. 30 to 40 km/h southwest ridgetop wind. Treeline temperature -4 °C. Freezing level 500 m.

Monday

Mostly cloudy with isolated flurries, 0 to 3 cm snow. 20 to 30 km/h south ridgetop wind. Treeline temperature -2 °C. Freezing level 1100 m.

Tuesday

Mostly cloudy. 10 to 20 km/h southeast ridgetop wind. Treeline temperature +1 °C. Freezing level 1400 m.

Wednesday

Mix of sun and cloud. 10 to 20 km/h north ridgetop wind. Treeline temperature +1 °C. Freezing level 1400 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
  • Avoid steep convex slopes.
  • Be alert to conditions that change with elevation and sun exposure.
  • Cornice failures could trigger very large and destructive avalanches.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.