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Avalanche Forecast

Archived

Feb 24th, 2023–Feb 25th, 2023

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

Regions

Kananaskis, Bow Valley, Highwood Pass, North 40, Spray - KLakes.

Now isn't a great time to expose yourself to avalanche terrain. The hazard is rated as Considerable, but it's a blurry line right now. It could easily jump to High with our current weather pattern.

Confidence

Moderate

Avalanche Summary

The wind shift last night triggered a very widespread avalanche cycle. We lost track of counting after 18 separate observations. Common details:

  • Alpine and upper treeline, N-E aspects

  • Many started mid start zone or even in the track.

  • Up to sz3, with most around sz2

  • Appeared to be within the windslabs only. 30-50cm deep on average

  • Most ran to mid run out

  • wide and erratic propagations

Snowpack Summary

As expected the winds shifted last night with dramatic results. It appears that wind slabs formed almost immediately on aspects from N to SE. A very widespread avalanche cycle occurred overnight as these new slabs didn't bond well with the older surfaces. To be completely honest, we're not exactly sure why the avalanche cycle was so widespread, but we suspect it was a combination of a very quick change in wind direction and a spike in intensity. Other factors may be temperature change(inversion possibly), or even different snow characteristics from the two distinct storm waves. In any case, we do know without question that we have a widespread windslab problem in the alpine and treeline areas. These slabs will be touchy for some time and very prone to human triggering. In other snowpack news, below treeline and sheltered areas have 20-30cm of settled storm snow resting on facets and depth hoar. Sudden collapses have been noted while trail breaking.

Weather Summary

Saturday will see the temperatures rise to about -12 by early afternoon. So far it looks like it will be a slow, but steady temperature rise throughout the evening/night. Skies should be clear tomorrow with maybe a little bit of afternoon cloud. And how 'bout those winds? Glad you asked. They will stick with us and even increase a bit tomorrow. Ridge winds will be strong and treeline winds will be moderate, but with strong gusts. All from the west.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.