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Avalanche Forecast

Archived

Dec 24th, 2023–Dec 25th, 2023

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

Regions

Purcells, Esplanade, Dogtooth, East Purcell, West Purcell.

Numerous, large persistent slab avalanches have been reported in the northern portion of this region in recent days.

Conservative terrain choices will be the key to playing safe.

Confidence

Moderate

Avalanche Summary

There have been numerous natural and skier triggered very large(up to size 3) persistent slab avalanches reported on all aspects at treeline and above in the Esplanade range over the past week. They have been failing on a weak layer of surface hoar down 50-70 cm.

This weak layer is a concern throughout much of the region.

A few naturally triggered wind slab avalanches up to size 2 were reported on easterly aspects in the alpine on Saturday.

Snowpack Summary

5-15 cm of new snow on Saturday and strong northwest wind formed fresh wind slabs on lee features at treeline and above.

The primary layer of concern in much of this region is a weak layer of surface hoar down 50-70 cm. This layer may be less likely to trigger in areas that have a strong, supportive crust above.

In the southern portion of the region, weak facets near the ground may be the primary layer of concern. Especially in shallow, rocky areas in the alpine.

Average snowpack depths at treeline are 70-120 cm which tapers rapidly below treeline.

Weather Summary

Christmas Eve

Mostly clear skies, southwest alpine wind 20 km/h, treeline temperature -15 °C.

Christmas Day

Mostly sunny skies, southwest alpine wind 20 km/h, treeline temperature -10 °C.

Tuesday

Mix of sun and cloud, west alpine wind 30 km/h, treeline temperature -8 °C.

Wednesday

Sunny skies, south alpine wind 20 km/h, treeline temperature -8 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.