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Avalanche Forecast

Archived

Jan 15th, 2023–Jan 16th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

Natural avalanche activity is tapering off, but there are a few surface hoar layers in the upper snowpack that will require some time to stabilize, stick to conservative, low consequence terrain. The possibility of avalanches stepping down to deeper weak layers persists, and would result in large destructive avalanches.

Confidence

Moderate

Avalanche Summary

Natural avalanche activity tapered off on Sunday with less inputs (cooler temps, minimal snow and light winds).

A fairly active avalanche cycle occurred Friday night until Saturday evening with numerous size 2-3 and one size 3 out of the steep terrain on Mt. MacDonald and Mt. Tupper, with some of these running over the snow sheds and full path into the creek. Elsewhere in the Park there were several size 1.5-2.0 from Mt. Smart, Ross Peak, Mt. Abbott and Cougar Mountain.

Snowpack Summary

~20cm of settled snow buries the Jan 12 surface hoar, and the Jan 3 surface hoar is ~20cm below that. The mid-pack consists of rounding facets and is gaining strength, while the bottom of the snowpack is weak and facetted with the Nov 17 facet/crust/surface hoar. This layer is ~50cm above the ground and has become less reactive in tests, but still shows 'sudden' results when it does fail.

At tree line there is ~160cm, which is 70% of an average snowpack

Weather Summary

Monday will be mainly cloudy with isolated flurries and sunny periods. Ridge-top winds will be light from the Southwest with alpine temps ranging from -10 to -6. Freezing level will reach up to ~1400m.

A ridge of high pressure builds on Tuesday into the end of the week.

Terrain and Travel Advice

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Use caution when approaching steep and rocky terrian.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

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.