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Avalanche Forecast

Archived

Mar 17th, 2023–Mar 18th, 2023

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

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

Avoid steep open slopes capable of producing large avalanches. Storm snow is expected to remain reactive.

Keep decision making conservative and give the snowpack time to stabilize.

Confidence

Moderate

Avalanche Summary

We expect a natural avalanche cycle occurred over the day on Thursday during periods of rapid loading. Natural activity could continue into Friday with more snow followed by sunny conditions. Human triggering is very likely given the amount of new snow and what it is resting on.

Natural avalanche activity could continue during periods of intense sun or wind loading. Avoidance of avalanche terrain is recommended until the snowpack has time to adjust.

Snowpack Summary

Around 50 cm of storm snow has fallen around White Pass, with lesser amounts as you move east. Southerly winds have built deeper deposits north facing terrain features near ridges. Storm snow overlies previously wind affected snow (sastrugi) in exposed areas and faceted snow in sheltered features. The new snow may not bond well to these previous surfaces.

The storm snow is also loading a buried weak layer of surface hoar found about 80 cm deep in Powder Valley, Tutshi, and Paddy Peak areas and approximately 150 to 200 cm around White Pass. This layer is most prominent on northerly slopes sheltered from the wind. On other aspects, this layer is a hard melt-freeze crust with weak facets around it. To date this layer is has been most problematic in alpine terrain.

The remainder of the middle of the snowpack is consolidated and strong. Weak faceted grains are found near the base of the snowpack, particularly in thin snowpack areas.

Weather Summary

Friday Night

Cloudy, with strong southerly winds. Freezing levels drop to valley bottom. Up to 3 cm of snow overnight.

Saturday

Partly clear skies with moderate southeast winds. Freezing levels reach 800 m, alpine high temperatures of -7 °C.

Sunday

Cloudy with light southeast winds. Up to 5 cm of snow. Freezing levels reach 800 m.

Monday

Cloudy. Light snowfall continues with light and variable winds. Freezing levels around 500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Be aware of the potential for large, deep avalanches to run full path or even longer.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.