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Avalanche Forecast

Archived

Jan 20th, 2020–Jan 21st, 2020

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

Regions

North Rockies.

Use extra caution in steep and open terrain as strong wind and warming temperatures are creating unstable slabs.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

MONDAY NIGHT: Partly cloudy, moderate wind from the southwest, freezing level drops to valley bottom and alpine temperatures drop to -8 C.

TUESDAY: Cloudy with light flurries in the afternoon, moderate wind from the south, alpine high temperatures around -4 C.

WEDNESDAY: Mix of sun and cloud, moderate wind from the southwest, alpine high temperatures around -4 C.

THURSDAY: Periods of snow with 5-10 cm of new snow, strong wind from the south, freezing level up to 1500 m and alpine high temperatures around -2 C.

Avalanche Summary

Several natural wind slabs were reported on a range of aspects at treeline elevations over the weekend. The most recent report of a persistent slab avalanche was last Tuesday, where a size 2 avalanche was observed on a south-facing slope at 1750 m near Crescent Spur. There have also been a number of glide cracks that failed naturally as very large avalanches in the Torpy area recently. Glide cracks are seemingly unpredictable and need to be given a wide berth. There are some great photos on the PGBCSki FB page. Mild temperatures this week could increase the sensitivity of persistent and glide slabs.

Snowpack Summary

Recent snow has settled with warm temperatures and been blown around by wind from various directions, resulting in wind slabs on all aspects at and above treeline. A weak layer of surface hoar buried in late December remains a concern. The layer has been found across much of the North Rockies region, but it has only become a problem in particular areas, such as around McBride and the McGregors/Torpy. It seems to be most prevalent in sheltered treeline features 50 to 150 cm below the surface.

Terrain and Travel

  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Avoid steep slopes when air temperatures are warm, it is raining, or solar radiation is strong.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.