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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 unlikely, human triggered possible.
Below Treeline
Below Threshold.

Regions

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Give large and/or steep slopes a wide berth. New snow will take time to settle, and wind will continue to keep hazard elevated. Watch for signs of instability like cracking in the new snow and assume that a small avalanche could trigger larger slopes and deeper layers.

Confidence

Moderate

Avalanche Summary

On Friday our field team witnessed a wide spread natural avalanche cycle on all aspects in the alpine and tree line up to size 3 with the most impressive propagation in large connected cross-loaded and lee features . Natural activity could continue into the weekend but the bond will improve over time. Human triggering will remain possible given the amount of new snow and what it is resting on.

Snowpack Summary

Thursday's substantial storm dropped upwards of 50 cm of snow around the Haines Pass with rain falling on top of the snow up to 700m, amounts tapered as you move inland, which has once again become a scoured area with only soft snow in sheltered gullies and side valleys.

Southerly wind accompanied the storm, and continued into Friday meaning deeper deposits may exist in lee terrain features near ridges. All this snow overlies previously wind affected snow (sastrugi) in wind affected areas and faceted snow in sheltered features. The new snow has not bonded well to these previous surfaces.

The storm snow is also loading a buried weak layer of surface hoar found about 80 cm to 200 cm around around Haines 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 and a thick melt freeze crust is next to the ground up to 20cm thick.

Weather Summary

Friday Night

Cloudy, with moderate to strong southerly winds. Freezing levels drop to valley bottom. Up to 5 cm of snow overnight.

Saturday

Partly clear skies with moderate to strong 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 700 m, alpine high temperatures of -8 °C.

Monday

Cloudy to start with clearing skies in the afternoon. 5 cm possible over Sunday night, easing in the morning. Light southerly winds. Freezing levels around 500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large, deep avalanches to run full path or even longer.
  • Don't let the desire for deep powder pull you into high consequence terrain.

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.