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Avalanche Forecast

Archived

Jan 11th, 2023–Jan 12th, 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 and human triggered avalanches likely.
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.

Regions

Glacier.

The weather and snowpack conditions are changing, and so should our mindset! The new snow will struggle to bond to old weak surfaces, expect sluffing in steep unsupported terrain. Fresh storm slab activity and the avalanche hazard will increase over the next few days.

Confidence

Moderate

Avalanche Summary

Explosive stability tests today produced six size 1-2 avalanches. They were very soft slabs failing on the Jan 3rd Surface Hoar which is buried ~15cm. 1 explosive-triggered avalanche stepped down to the Nov 17th PWL, 1m deep, and was a size 3

A dozen avalanches were recorded in the Highway Corridor on Jan 10th and 11th. Most of them were from extreme terrain on Mt Mcdonald and Mt Tupper.

No new avalanches were reported from the Back Country in Glacier National Park on January 10th or 11th; However, There were several avalanches reported on the 8th and 9th in the immediate vicinity of Rogers Pass. The nature of avalanches was wind slabs to persistent slab avalanches, with many large enough to injure or kill a person.

Snowpack Summary

Storm slabs will be built throughout Thursday, Friday, and Saturday as continued new snow buries a weak layer of low-density snow and the Jan 3rd Surface Hoar.

The December 23rd facet interface is down ~60cm and appears to be gaining strength, but remains a concern in shallow snowpack areas.

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

Finally, some snow is in the forecast! On Thursday we should see, 10-15cm of new snow, the freezing level rising to ~1500m, and moderate to strong winds from the SW. Friday's forecast is very similar with another 15cm with similar winds and freezing levels. Only 5cm on Saturday, then it should dry up on Sunday as the storm passes by Rogers Pass.

Terrain and Travel Advice

  • Be carefull around freshly wind loaded features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.