Avalanche Canada shorton, Avalanche Canada

North Rockies Avalanche Forecast

Dec 20th, 2019 4:00PM

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

The stormy weather has ended, but human triggered avalanches are still likely in steep and open terrain. A cautious approach to backcountry travel is recommended.

Summary

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

FRIDAY NIGHT: Partly cloudy, 30-50 km/h wind from the southwest, alpine temperatures drop to -8 C.

SATURDAY: Mix of sun and cloud with some isolated flurries in southern parts of the region, 20-40 km/h wind from the southwest, alpine high temperatures around -4 C.

SUNDAY: Mix of sun and cloud, 20-40 km/h wind from the west, alpine high temperatures around -6 C.

MONDAY: Mix of sun and cloud, light wind, alpine high temperatures around -6 C.

Avalanche Summary

Recent reports include natural wind slab avalanches in steep alpine terrain (see this MIN report) and touchy storm slabs around Hasler (see this MIN report). As we move out of the stormy period, natural avalanches are still possible in wind affected alpine terrain, while human triggered avalanches remain a concern at all elevations.

Please share you observations and photos from this weekend on the Mountain Information Network!

Snowpack Summary

Stormy weather the past few days delivered 20-30 cm of new snow to most parts of the regions, with some areas receiving up to 50 cm (e.g. around Pine Pass). Steady wind from the southwest is likely blowing this snow into unstable wind slabs in open terrain, while soft powder will be preserved in sheltered areas.

The storm snow sits above three weak layers buried between 30 and 60 cm below the surface. These surface hoar and facet/crust layers showed signs of being reactive prior to the storm and have the potential to produce large avalanches the next few days while they adjust to the weight of the new snow. Reports suggest these layers are widespread around Pine Pass and the McGregors, but harder to find around McBride. 

The lower snowpack contains several crust layers. In higher snow areas, these are likely well bonded. However, in shallow areas along the eastern slopes, these could be of concern.

Total snowpack depths are approximately 240 cm in the south of the region, 170 cm around Pine Pass and more like 120 cm in areas to the east.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Give the new snow several days to settle and stabilize before pushing into bigger terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 2

Moderate to strong wind from the southwest has likely formed unstable wind slabs in open terrain, particularly behind exposed ridges.

Aspects:

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

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

1.5 - 3

Weak layers of surface hoar exist in the upper snowpack, especially around Pine Pass and the McGregors. These layers are most likely to be triggered on steep convex slopes at or below treeline that have not previously been well ridden.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Dec 21st, 2019 4:00PM