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Avalanche Forecast

Archived

Apr 14th, 2013–Apr 15th, 2013

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.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

This bulletin was produced using limited data streams, and significant variations in snowpack structure are likely to exist. If you've been traveling in the backcountry, we'd love to hear from you. Observations can be sent to [email protected].

Confidence

Fair - Due to limited field observations

Weather Forecast

A ridge of high pressure is expected to develop throughout the forecast period. Overcast skies and light convective flurried are possible on Monday giving way to a mix of sun and cloud on Tuesday and Wednesday. Generally light east/northeast winds are expected each day. Daytime freezing levels are meant to climb gradually from about 1000m on Monday to about 1600m on Wednesday.

Avalanche Summary

In recent days, explosives control has produced slab avalanches to size 2 on northeast facing slopes at 2600m and higher. These slabs likely failed on the early April surface hoar. Wind slabs to size 1.5 were also triggered on north facing alpine slopes. In general, observations have become very limited.

Snowpack Summary

Light to generally moderate snow accumulations from Friday night have been shifted by variable winds into windslabs which exist at treeline and above. In some areas ongoing snowfall throughout the weekend has produced overlying soft slabs.A surface hoar interface is buried within the upper metre of the snowpack, mainly on high-elevation northerly aspects. Although it may be gaining strength, these slopes should be treated with suspicion particularly in deep snowpack areas where the overlying slab is well developed. On other slopes, recent storm snow overlies a crust.

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.