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Avalanche Forecast

Archived

Feb 4th, 2023–Feb 5th, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

North Rockies, Kakwa, McGregor, Pine Pass.

Ongoing snowfall in the past week has added significant load to a weak and volatile snowpack.

Reactive storm slabs may be evident underfoot, but keep the potential for large, destructive deep persistent avalanches in the forefront of your mind.

Confidence

Moderate

Avalanche Summary

In the Pine Pass area, heavy snowfall caused a natural avalanche cycle that started on Thursday that continued into Saturday morning. Reports from Thursday indicate storm slabs were very reactive to snowmobile traffic, producing many size 1 to 1.5 storm slab avalanches that propagated widely.

With heavy snowfall continuing throughout the day on Sunday, we expect dangerous avalanche conditions to persist. Human-triggered avalanches will be very likely on steep slopes and natural avalanches will likely continue on wind-loaded slopes. Storm slab avalanches could step down to the facets near the base of the snowpack, producing very large avalanches. See more on the potential of triggering deeper weak layers in our latest Forecasters' Blog.

Snowpack Summary

Stormy weather over the past week has brought 40 to 80 cm of new snow to the region. Snowfall will continue throughout the day bringing an additional 10-15 cm. Warm windy weather is causing this storm to settle into reactive slabs. The storm snow sits on previously wind-affected snow. Below this, a melt-freeze crust is found on sun-exposed slopes and everywhere below 1600 m.

Several crust/facet/surface hoar layers exist in the upper and middle portions of the snowpack. Recent observations suggest these layers are gaining strength, but remain on our radar as active loading continues.

The most concerning persistent weak layer is at the base of the snowpack from large and weak facets formed in November. This layer is widespread and most likely problematic in steep, rocky alpine and upper treeline terrain.

Weather Summary

Saturday night

Mainly cloudy with flurries, up to 5 cm of accumulation. Alpine temperatures drop to -6 C. Ridge wind southwest 30-70 km/h. Freezing level drops to 1300 m.

Sunday

Cloudy with snowfall, heavy at times, with 10-15 cm of accumulation. Alpine temperatures are around -6 C. Ridge wind southwest 40-70 km/h. Freezing level 1200 m.

Monday

Cloudy with snowfall, up to 10 cm accumulation. Alpine temperatures reach a high of -3 °C. Ridge wind 30 to 80 km/h. Freezing level 1400 metres.

Tuesday

Cloudy with snowfall, heavy at times, with 5-15 cm of accumulation. Alpine temperatures are around -10 C. Ridge wind west 10-30 km/h. Freezing level 1000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.

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.

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.

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.