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Avalanche Forecast

Archived

Feb 17th, 2021–Feb 18th, 2021

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

Regions

South Rockies.

It's going to be a sunny day! However, slabs on the late January persistent weak layer and wind slabs are still reactive to human triggers. Don't let your guard down just yet. Read our forecaster blog on "Managing Moderate". Join us for our South Rockies webinar Thursday evening.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

WEDNESDAY NIGHT: Clear with cloudy periods, moderate northwest wind, temperature low -21 C.

THURSDAY: Mostly sunny, moderate westerly wind, temperature high -9 C.

FRIDAY: Mix of sun and cloud, trace of new snow, moderate southwest wind, temperature high -5 C.

SATURDAY: Mostly sunny with cloudy periods, trace of new snow, moderate southwest wind, temperature high -5 C.

Avalanche Summary

On Tuesday a couple wind slab avalanches of size 2 were triggered by explosives. 

Several wind slab avalanches up to size 2 were triggered by skiers and released naturally at treeline and in the alpine on Monday. Human triggered avalanches were reported north of Crowsnest Pass. The avalanches were triggered on east aspects on mellow slopes in the alpine and at the treeline/alpine interface (see this MIN report). The failure plane of these avalanches is likely the late January persistent weak layer consisting of surface hoar, sugary facets or a crust/facet combination. 

Several skier triggered wind slab avalanches up to size 1.5 were reported on Sunday on usually and reverse loaded terrain features. Older natural avalanche activity of up to size 3 was reported as well on Sunday dating back a couple days. Reports on whumpfing and cracking of the upper snowpack were varied. Some parties experienced whumpfs and cracks (see this MIN report) whereas others didn't (see this MIN report).

A skier accidentally triggered a size 1.5 wind slab in a reverse loaded feature on the Alberta side of the region on Saturday.

Snowpack Summary

The snow surface is wind affected, especially in the alpine and open areas at treeline. Cold temperatures promote faceting of the snow surface. A persistent weak layer lurks 40-65 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack. Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be approached with caution.

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.

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.