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Avalanche Forecast

Archived

Apr 7th, 2021–Apr 8th, 2021

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

Regions

North Rockies.

Watch for reactivity in wind-affected snow this week as incremental snowfall continues to accumulate.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night: Scattered flurries with up to 5 cm new snow. Moderate southwest wind. Treeline temperatures around -5 C. Freezing level valley bottom.

Thursday: Mostly cloudy skies with isolated flurries. Moderate southwest wind increasing into the evening. Treeline temperatures around -5 C. Freezing level 1200 m.

Friday: 5-15 cm new snow. Strong overnight wind easing to moderate southwest over the day. Treeline temperatures around -3 C. Freezing level 1400 m.

Saturday: 5-15 cm new snow overnight. Moderate northwest wind. Treeline temperatures around -5. Freezing level 1100 m.

Avalanche Summary

Reports from Monday and Tuesday include:

  • Numerous loose wet avalanches size 1-2 on solar aspects and low elevations in the afternoon
  • Numerous loose dry to size 1.5 on steep northerly alpine aspects
  • Evidence of several large cornice failures but no slabs were triggered on slopes below

On Saturday the North Rockies field team reported a wind slab avalanche on an east-facing slope at Renshaw that was a few days old. Otherwise the only other recent reports of avalanches have been from a natural cycle of storm slab avalanches that occurred at the end of March in northern parts of the region.

Snowpack Summary

Crusty conditions on all but steep north facing terrain above 1700 m was reported in this MIN report from Tuesday. Another 5-15 cm forecast overnight Friday will add to the settling 10-30 cm that fell incrementally over the past week. This recent snow sits on crusts at lower elevations and on solar aspects. Unstable slabs may be found on wind loaded features at upper elevations.

Recent weather patterns have helped previous weak layers strengthen, including the mid-February facet layer that is now roughly 150 cm deep. However, it may still be possible to trigger avalanches on basal layers in shallow rocky terrain along the eastern slopes of the Rockies.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Be alert to conditions that change with aspect and elevation.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.