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Avalanche Forecast

Archived

Mar 20th, 2023–Mar 21st, 2023

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

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

Hazard is improving as temperatures drop down to the valley bottom but be mindful that deep instabilities are still present.

Use caution around wind loaded terrain where windslab may be reactive to skier traffic.

Confidence

Moderate

Avalanche Summary

On Sunday, a suspected skier triggered avalanche was reported. This was a size 1 storm slab avalanche that likely occurred on Saturday.

Through the weekend we continued to receive reports of evidence of large storm slab and wind slab avalanches, size 2-3, in both Haines Pass and White Pass. These avalanches may have occurred during the storm or due to solar input and elevated freezing levels through the weekend.

If you head out in the backcountry, let us know what you are seeing by submitting a report to the Mountain Information Network.

Snowpack Summary

Up to 50 cm of storm snow at White Pass and +50 cm at Haines Pass from last week has settled rapidly with warm temperatures. Storm totals taper inland in both regions. Local wind patterns have varied from southerly in White Pass to easterly in Haines Pass, building wind slabs in exposed lee terrain. This overlies previously wind affected snow (sastrugi) in exposed areas and faceted snow in sheltered features.

A buried weak layer of surface hoar can be found about 80 cm deep in Powder Valley, Tutshi, and Paddy Peak areas, 150 to 200 cm around White Pass and 80-200 cm deep in Haines Pass. This layer is most prominent on northerly slopes sheltered from the wind. On other aspects, this layer is a hard melt-freeze crust with weak facets around it. This layer has been most problematic in alpine terrain.

The remainder of the middle of the snowpack is consolidated and strong. Weak faceted grains are found near the base of the snowpack, particularly in thin snowpack areas.

Weather Summary

Monday Night

Cloudy with isolated flurries, 1-3 cm accumulation. Moderate southwest winds. Alpine temperature low -6°C. Freezing levels drop to valley bottom.

Tuesday

Mainly cloudy. Strong southwest winds. Alpine temperature high -7°C. Freezing levels valley bottom.

Wednesday

Cloudy with isolated flurries, 1-3 cm accumulations. Strong southwest winds. Alpine temperature high -4°C. Freezing levels 600 m.

Thursday

Cloudy with isolated flurries, trace accumulations. Strong south winds. Alpine temperature high -3°C. Freezing levels 800 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Be carefull around freshly wind loaded features.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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.