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Avalanche Forecast

Archived

Feb 4th, 2025–Feb 5th, 2025

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

Regions

Purcells, Esplanade, Dogtooth, East Purcell.

New snow overlies a prominent weak layer in sheltered areas at treeline and below. Avoid areas where snow feels stiff or slabby.

Check out the Forecaster Blog Keeping a Conservative Mindset.

Confidence

High

Avalanche Summary

On Monday, a few human-triggered size 1 wind slab avalanches were reported in northerly alpine and treeline features. Avalanche control produced several explosive-triggered persistent slab and dry loose avalanches, up to size 1.5.

A size 2 natural wind slab avalanche was observed in northeast-facing alpine terrain.

We expect unconsolidated snow will remain reactive to skier traffic on Wednesday in steep terrain. Carefully manage sluffing in steep terrain.

Snowpack Summary

Storm snow totals range from 30 to 50 cm, with deeper deposits in wind-loaded areas. The new snow is bonding poorly to old surfaces, which include melt-freeze crusts on sun-exposed slopes, surface hoar or facets on shaded slopes, and wind-affected snow at higher elevations.

A weak layer of surface hoar of facets is buried, 30 to 60 cm deep. Where this layer is preserved it may be reactive to human triggering.

A weak layer of facets from early December is buried 60 to 120 cm deep.

The base of the snowpack consists of a thick crust with facets or depth hoar in many areas.

Weather Summary

Tuesday Night

Partly cloudy with a chance of flurries, 0 to 1 cm of snow. 10 to 15 km/h variable ridgetop wind. Treeline temperature -20 °C.

Wednesday

A mix of sun and cloud. 10 to 25 km/h west ridgetop wind. Treeline temperature -16 °C.

Thursday

Mainly sunny. 10 to 15 km/h northwest ridgetop wind. Treeline temperature -15 °C.

Friday

Mainly sunny. 5 to 15 km/h northwest ridgetop wind. Treeline temperature -15 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Pay attention to the wind; once it starts to blow, sensitive wind slabs are likely to form.
  • Avoid freshly wind-loaded terrain features.
  • Be aware of the potential for remote triggering and large avalanches due to buried surface hoar.
  • Keep in mind that human triggering may persist as natural avalanches taper off.

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.