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Avalanche Forecast

Archived

Feb 18th, 2017–Feb 19th, 2017

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

Regions

Little Yoho.

http://www.pc.gc.ca/apps/links/goto_e.asp?destination=

Potential for large avalanches persist. Conservative route choices remain the theme of the day.

Weather Forecast

5-10 cm is possible on Sunday at higher elevations with freezing levels to 1700m and light SW winds. Another system Tuesday may bring 10 more cm if the forecast holds true...

Snowpack Summary

40-60 cm of snow in the past week combined with mod SW winds created windslabs on lee and crossloaded features. This rests on hard windslabs at treeline and above which overly a structurally weak mid-pack. Below 1900m a surface crust has formed from the previous rain and warming event on Thursday, and subsequent cooling.

Avalanche Summary

Several avalanches in the BYK region in the past 48 hrs, some stepping down to deep persistent layers and the ground. A rain event on Thursday triggered a loose wet cycle below 1900m in the Field area. With cooling over the last 2 days the natural activity has slowed and no new avalanches were reported in that area Saturday.

Confidence

Intensity of incoming weather systems is uncertain on Sunday

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.