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Avalanche Forecast

Archived

Jan 12th, 2023–Jan 13th, 2023

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

Regions

Glacier.

The weather and snowpack conditions are changing, and so should our mindset!

The new snow will not likely bond well to previous weak surfaces. Expect fresh storm slab activity, and the possibility of avalanches stepping down to deeper weak layers, producing large destructive avalanches.

Confidence

Moderate

Avalanche Summary

There were about a dozen avalanches recorded in the Highway corridor January 10th-12th. Most of them were from extreme terrain on Mt MacDonald and Mt Tupper. Notably, there was a size 3.0 slab avalanche from MacDonald gully #10 on Thursday, which ran well on to the fan.

On Wednesday, explosive stability tests produced six size 1-2 avalanches. They were mostly very soft slabs failing on the Jan 3rd Surface Hoar which was down about 15cm. The 7th explosive scrubbed down to ground on a shallow rocky rib, and then stepped down to the Nov 17th PWL, 1m deep, resulting in a size 3.

No new avalanches were reported from the back country in Glacier National Park on January 10th-12th. However, there were several avalanches reported in the immediate vicinity of Rogers Pass. These were mostly wind slab and persistent slab avalanches, with many large enough to injure or kill a person.

Snowpack Summary

Storm slabs will continue to build through until early Saturday morning, as continued new snow buries two weak layers of Surface Hoar (January 3rd and 12th) separated by 10-25cm of previous low density snow.

The December 23rd facet interface is down ~60cm and appears to be gaining strength. This layer remains a concern in shallow snowpack areas, where the mid and lower snowpack are made up primarily of weak facetted crystals.

The November 17th facet/crust/surface hoar layer is down ~100cm and has become less reactive in snowpack tests. When it does fail, there is a dramatic 'drop' of the entire snow column. Spooky!

Weather Summary

On Friday the snowfall rates should peak, with an additional 10cm forecast to fall, along with moderate to strong SW ridgetop winds, and freezing levels possibly climbing as high as 1800m.

An additional 5cm is forecast for Saturday, with light winds and a 1600m freezing level.

On Sunday, temperatures cool and the sun should make an appearance later in the day, as the storm moves past Rogers Pass.

Terrain and Travel Advice

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Carefully manage your exposure to overhead hazards while entering and leaving riding areas.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.