Avalanche Forecast

Archived

Apr 2nd, 2021–Apr 3rd, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

North Rockies.

There is lots of new snow available for the wind to redistribute into lee terrain. As a result wind slabs at upper elevations will be the main concern when the wind speed picks up.

Confidence

Moderate - Uncertainty is due to limitations in the field data.

Weather Forecast

Friday Night: Mostly cloudy with some clear periods. Light to moderate southwest wind. Freezing level valley bottom. Alpine temperature -8.

Saturday: Mostly cloudy with scattered flurries, accumulation 2-5 cm. Light to moderate southwest wind. Freezing level 1200 m. Alpine temperature -4.

Sunday: Partly cloudy. Moderate to strong west wind. Freezing level 1400 m. Alpine temperature -3.

Monday: Mostly cloudy. Moderate southwest wind. Freezing level 1500 m. Alpine temperature -2.

Avalanche Summary

There are no recent reports of avalanche activity, although with recent snow and wind there is likely natural wind slab activity at upper elevations.

Evidence of large storm slab avalanches (size 3) was observed Monday and Tuesday between Sentinel Pass and Chetwynd, likely having released during the storm on the weekend.

Snowpack Summary

10-40 cm of recent snow earlier in the week has been redistributed by strong southwest to northwest wind with wind slabs possible on many aspects and large, fragile cornices along ridgetops. This snow sits on melt freeze crusts at lower elevations and on solar aspects.

A weak layer of facets buried in mid-February may now be found around 120 to 150 cm deep, or shallower in the east of the region and in thin snowpack areas. The most likely place to trigger this layer is where the snowpack is shallow in alpine terrain. Large loads, such a cornice falls or multiple sleds on the same slope often trigger slopes that a single rider couldn't trigger on their own.

Terrain and Travel

Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
Be aware of highly variable recent wind loading patterns.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.