Parks Canada tim haggarty, Parks Canada

Little Yoho Avalanche Forecast

Jan 13th, 2020 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Persistent Slabs, Wind Slabs and Deep Persistent Slabs.

Both superficial and basal problems exist in the snowpack right now and both can be expected to persist for some time. Conservative terrain selection, careful snowpack evaluation and cautious group management is essential for safe travel.

Summary

Weather Forecast

The Polar air continues to push from the prairies over the divide. Mixing with pacific air is creating thin cloud and very light snowfall. Lack of sunshine, combined with brisk winds, increasing Tuesday through Wednesday, will make the cold hard to deal with although the possibility of inversion may hold for Tuesday.

Snowpack Summary

30-50 cm of snow since Dec 31 sits over a variety of surfaces including facets, surface hoar and sun crust. Stability tests throughout the region show 'sudden planar' results on this interface. Reactive wind slabs exist in alpine and some tree line locations. In most areas there is a settled mid-pack over top of weaker basal layers.

Avalanche Summary

Parks Canada responded to a size 2.5 skier triggered avalanche on the South flanks of Mt. Hector Friday. This avalanche failed to the ground in the upper start zone and track.

Several naturals sz 2-3 were observed Thursday throughout the forecast region, some of which failed at the ground within the deep persistent layer.

Confidence

Due to the number of field observations

Problems

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Likely - Possible

Expected Size

1 - 2.5

This layer may present as surface hoar / facets / or sun crust. It is buried 30-60 cm throughout the region and is producing 'sudden planar' results in stability tests. Several skier triggered avalanches have occurred recently on this layer.

  • Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.
  • If triggered the persistent slab may step down to deeper layers resulting in large avalanches.

Aspects:

All aspects.

Elevations:

Treeline, Below Treeline.

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely - Possible

Expected Size

1 - 2.5

Recent storm snow and moderate to strong winds have created wind slabs in the alpine and at treeline elevations. It will take several days for these instabilities to settle out.

  • If triggered, the wind slab may step down to deeper layers resulting in large avalanches.
  • Use caution in lee areas. Recent wind loading has created reactive slabs.

Aspects:

North, North East, East, South East, South, North West.

Elevations:

Alpine, Treeline.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3.5

The potential for deeper releases on the basal layers still exist although thicker snowpack areas in the region show less development of this weakness. Several large avalanches have occurred on this layer in past few days :see "Forecast Details".

  • Avoid shallow snowpack areas where triggering is more likely.
  • Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Jan 14th, 2020 4:00PM