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Avalanche Forecast

Archived

Jan 29th, 2023–Jan 30th, 2023

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

Regions

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

6:30 AM PST UPDATE: A weak layer of surface hoar is buried at a prime depth for human-triggering as well as large consequential avalanches.

The most activity has been noted on northerly alpine slopes, but until we gain more information about this layer riders should take a very cautious approach to avalanche terrain. Check out this MIN report from the Avalanche Canada field team on Friday.

Confidence

Moderate

Avalanche Summary

Numerous large (size 2-3) natural and human-triggered persistent slab avalanches have been reported in the past 3 days. These avalanches are failing on a weak layer of surface hoar with a crust below.

Snowpack Summary

In alpine terrain, recent winds have created a variety of wind-affected surfaces. Wind slabs remain in steep, lee terrain features and may be burying isolated pockets of preserved surface hoar. The surface hoar is reported to be roughly 50 to 80 cm down from the surface. Below roughly 1700 m a widespread, melt-freeze crust is present, with moist snow below.

Weather Summary

Sunday night

Becoming overcast, with flurries beginning in the early morning. Treeline temperatures -5 to -10 C. Moderate west alpine winds.

Monday

Cloudy, with flurries, 0 to 2 cm. Treeline temperatures -5 to -10 C. Moderate westerly alpine winds.

Tuesday

Cloudy, with flurries, 0 to 2 cm. Treeline temperatures -5 to -10 C. Light southwest alpine winds.

Wednesday

Cloudy with sunny periods, no precipitation. Treeline temperature -10 to -15 C. Moderate alpine winds.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • In times of uncertainty conservative terrain choices are our best defense.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.

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.