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Avalanche Forecast

Archived

Jan 4th, 2023–Jan 5th, 2023

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

Regions

Glacier.

We have a very weak, faceted, basal layer in our snowpack at Rogers Pass.

Avoid thin, rocky, unsupported features where one could sink into the sugary facets, potentially triggering the deeper persistent weak layers.

Confidence

Moderate

Avalanche Summary

Several natural sz 2 slab and loose avalanches were observed in the highway corridor on Tuesday and Wednesday. Most were from steep, rocky S aspects, with the exception of a larger slab from Macdonald Gully 10.

On Monday a size 2 avalanche was remotely triggered from a shallow snowpack area on Bruins Ridge. These are the spooky avalanches that are causing anxiety amongst avalanche forecasters! Stay away from thin, rocky areas!

Snowpack Summary

The top 30cm of snow is low-density and provides great powder turns. Steeper SW and W aspects have a thin sun crust on the surface. The Dec 23 facet interface, down ~70cm, is gaining strength. The Nov 17 facet/crust/surface hoar layer is still active in snowpack tests, exhibiting 'sudden collapse' or 'sudden planar' results.

Weather Summary

Clouds, flurries, and slightly elevated freezing levels (FZL) will be the norm for the next few days. No major storms in the foreseeable future. Darn, eh!?

Thurs: mainly cloudy, trace snow, Alp high -2*C, 1600m FZL, light S winds

Fri: cloud with scattered flurries, 5cm, Alp high -4*C, 1500m FZL, light/gusty SW winds

Sat: flurries, 5cm, Alp high -4*C, 1600m FZL, light SW winds

Terrain and Travel Advice

  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.