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Avalanche Forecast

Archived

Jan 16th, 2023–Jan 17th, 2023

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

Regions

Glacier.

Two persistent weak layers (surface hoar) are buried in the upper 40cm. These layers take additional time to bond with the new snow, necessitating folks to stick to well-supported, lower-angled terrain lest they tickle the underbelly of the surface hoar beast.

Surface slabs have the potential to dig deeper, triggering the deep persistent slab, resulting in large, destructive avalanches.

Confidence

Moderate

Avalanche Summary

Natural avalanche activity has slowed, with isolated sz 1.5-2 soft slabs observed from mostly steep S'ly terrain. The weekend's avalanche cycle saw numerous sz 2-3 storm and persistent slabs ripping out of Mts MacDonald and Tupper. The west side of the Pass saw smaller results (sz 1.5-2) on Mts Smart, Abbott, Ross Pk, and Cougar Mtn.

Snowpack Summary

Two surface hoar (SH) layers, present in the upper 40cm, are potential failure planes if the new snow stiffens up on top of them. The mid-pack facets are slowly rounding and gaining strength, while the basal facets and Nov 17 facet/SH/crust weakness are still reactive when isolated in snowpack tests.

Weather Summary

The Coastal storms don't seem to have enough punch to get to the Pass. General cooling trend and isolated flurries this week.

Tues: mainly cloudy, trace snow, Alp high -8*C, 1100m FZL, light SW ridge winds

Wed: mix of cloud and sun, trace snow, Alp high -8*C, 1100m FZL, light SW ridge winds

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.