Avalanche Forecast

Archived

Feb 22nd, 2021–Feb 23rd, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Recently formed slabs will likely remain triggerable to riders on Tuesday. Conservative terrain travel is recommended!

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

MONDAY NIGHT: Cloudy with snowfall, accumulation 5 to 15 cm and local enhancements possible, 30 to 60 km/h southwest wind, alpine temperature -7 C, freezing level dropping to valley bottom.

TUESDAY: Mix of sun and cloud, 30 km/h west wind, alpine temperature -10 C.

WEDNESDAY: Clear skies, 20 km/h southwest wind, alpine temperature -10 C.

THURSDAY: Cloudy with snowfall, accumulation 5cm, 30 to 60 km/h southwest wind, alpine temperature -9 C.

Avalanche Summary

Much of the region wasn't visible on Sunday and Monday due to stormy conditions. Natural and human-triggered avalanches were probably during that period, particularly in the high-snowfall areas of the region. We may see the evidence of the activity as the skies clear on Tuesday.

Snowpack Summary

Anywhere from 5 to 40 cm of snow fell on Monday, with the most in the south and west of the region near the divide. Storm slabs likely developed rapidly for high snowfall areas and wind slabs formed everywhere with strong southerly wind. The freezing level hovered around 1500 m, soaking the snowpack below. More snow, strong west wind, and a dropping freezing level are forecast for Monday night, building these slabs into Tuesday. The snow overlies previously hardened snow from wind effect or sugary faceted grains in sheltered areas.

Around 50 to 80 cm deep, a weak layer of surface hoar may be found in sheltered terrain or otherwise faceted grains and/or a hard melt-freeze crust. This layer has so far shown to be most problematic around the Elk Valley, but you may find it elsewhere.

Weak faceted grains and a decomposing melt-freeze crust are likely found near the base of the snowpack. There have not been recent avalanche observations on this layer, but steep and rocky slopes as well as shallow snowpack areas should be approached with caution.

Terrain and Travel

Choose conservative terrain and watch for clues of instability.
Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.