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Avalanche Forecast

Archived

Jan 22nd, 2020–Jan 23rd, 2020

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

Regions

North Rockies.

New snow falling with wind and warm temperatures will continue to promote wind slab formation in exposed terrain over the next few days.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with clear periods, moderate wind from the southwest, alpine high temperatures around -4 C.

THURSDAY: Flurries, accumulation 5-15 cm, moderate wind from the southwest, freezing level up to 1500 m and alpine high temperatures around -2 C.

FRIDAY: Scattered flurries, moderate to strong wind from the southwest, freezing level up to 1600 m and alpine high temperatures around -2 C.

SATURDAY: Mainly cloudy, moderate to strong wind from the southwest, freezing level up to 1500 m and alpine high temperatures around -3 C.

Avalanche Summary

On Monday there were reports of numerous natural wind slab and cornice triggered avalanches running to size 2 in the alpine on a variety of aspects. See this MIN post for more details.

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

  • Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
  • Be careful as you transition into wind affected terrain.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.

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.