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Avalanche Forecast

Archived

Feb 15th, 2021–Feb 17th, 2021

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

Regions

North Rockies.

Travel cautiously - the snowpack is suspect and avalanches are possible in a wide variety of terrain. Read more about managing these conditions in this forecaster blog. 

Confidence

Moderate - A small change in the upper snowpack could dramatically change avalanche conditions.

Weather Forecast

A weak system crosses the region on Tuesday bring relatively warmer temperatures and some light flurries.

MONDAY NIGHT: Light flurries with 2-5 cm of snow in northern parts of the region, moderate northwest wind, treeline temperatures around -12 C.

TUESDAY: Clearing skies in the north with 2-5 cm of snow in the south, moderate northwest wind, treeline temperatures around -10 C.

WEDNESDAY: Sunny with a few clouds, light to moderate northwest wind, treeline temperatures around -8 C.

THURSDAY: Mostly cloudy, strong south wind, treeline temperatures around -6 C.

Avalanche Summary

There were a few reports of human triggered avalanches over the weekend including some small (size 1.5) sled triggered slab avalanches near Renshaw (MIN report) and some small dry loose avalanches in northern parts of the region where the persistent weak layer is shallowly buried. Prior to the cold snap, during the first week of February, there were numerous small human triggered avalanches on the same problematic persistent weak layer as well as some large natural avalanches. There are some great visuals of that activity in this MIN. 

Snowpack Summary

It's time to monitor subtle changes in the upper snowpack as we leave a prolonged cold snap. A dusting of new snow and northwest wind could make upper elevation wind slabs more reactive, while warming temperatures could promote more reactive slabs above the widespread persistent surface hoar layer. This layer is already 40 cm deep around Torpy and McBride, but only 15-25 cm deep further north. Reports suggest this layer is most prevalent around treeline elevations, but likely reaches into the alpine and down into the trees too. It may sit above a crust below 1600 m. There are presently no deeper concerns in the snowpack.

Terrain and Travel

  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Use ridges or ribs to avoid areas of wind loaded snow.

Problems

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.

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.