Avalanche Canada istorm, Avalanche Canada

North Rockies Avalanche Forecast

Dec 25th, 2019 5:00PM

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

Central and northern areas have weak layers 40 to 70 cm below the surface which remain a concern for triggering. Forecast winds are likely to build wind slabs throughout the region. Wind protected areas are your best bet for good riding! Merry Christmas & happy trails!

Summary

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure. Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

Small disturbances will bring some snow to the region starting on Thursday

WEDNESDAY NIGHT: Dry with light to moderate westerly wind and temperatures around -15 C.

THURSDAY: Wind becoming southwest and strengthening to moderate at treeline and strong at alpine elevations. Snow beginning with accumulations of 5 to 15 cm by Friday morning. Temperatures at treeline around -10 C.

FRIDAY: Similar to Friday with continued moderate to strong southwesterly winds and steady temperatures around -10 C. Light snowfall with accumulations between a trace and 5 cm, up to 10 cm in favoured upslope areas.

SATURDAY: Warmer with treeline temperatures warming to around -5 C and moderate SW winds. Only a trace to 5cm of new snow forecast.

Avalanche Summary

Last week's storm resulted in a natural avalanche cycle in Pine Pass and northern areas that released either at the bottom of the storm snow or in a deeper weak layer. In the south and west areas there were fewer reports of avalanches and they were small.

Looking forward, the weather forecast suggests strong wind events with some new snow; even without additional snow there's enough on the ground available for transport so I expect natural wind slab activity on lee slopes with it primed for human triggering.

Snowpack Summary

Northern and western areas of the North Rockies region received 30 to 50 cm of new snow last week, eastern and southern regions received much less with anywhere from a trace to around 25 cm. That means deeper snowpack areas have around 250 cm on the ground near treeline, thinner areas have around 100cm.

Layers of concern vary through the region too. Areas around Pine Pass and Tumbler have, within the top 40 to 80 cm, surface hoar and facet/crust layers formed in late November that are reactive in snowpack tests. We think they exist around treeline elevations throughout the region, and can likely be found in alpine terrain as well.

The lower snowpack contains several crust layers, which could be a concern in shallow areas along the eastern slopes of the region. Having said that, we have little to no information from places like Kakwa.

In the west (e.g. Torpy) and south (McBride) where the snowpack is deep it is also stronger and missing some of the weak layers.

Throughout the region a new layer of surface hoar is being buried -- here's a pic from our NoRo field team.

Terrain and Travel

  • Sheltered slopes at lower elevations will offer the best riding.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Caution around slopes that are exposed to cornices overhead.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely-Very Likely

Expected Size

1.5 - 2.5

Forecast strong southerly to westerly winds will build wind slabs in open terrain behind ridges and quite possible further dowslope away from ridge crests and in open areas near treeline.

Aspects:

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

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

1.5 - 3

Persistent problems are more common in thinner, colder snowpack areas of the region (for example Pine Pass, Tumbler Ridge, Kakwa) than in warmer and deeper areas (like Renshaw or Torpy).

Aspects:

All aspects.

Elevations:

Treeline, Below Treeline.

Valid until: Dec 26th, 2019 5:00PM