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Avalanche Forecast

Archived

Feb 6th, 2023–Feb 7th, 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 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.

Regions

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

Steady snowfall and elevated winds are building wind slabs in exposed areas. Seek out sheltered lower elevations free of overhead hazard. There's a definite chance of wind slab releases triggering a deeper snowpack layer to create larger, more destructive avalanches.

Confidence

Moderate

Avalanche Summary

This MIN discusses new wind slab formation. We expect wind slabs to increase in size and reactivity.

A couple of large (size 2-3) persistent slab, human-triggered and natural avalanches were reported last week. These avalanches occurred near ridgetops in north-to-northeast alpine terrain. These avalanches have shown an impressive capability to propagate across large distances. Here is a link to the most recent human-triggered size 3 avalanche.

If you are out in the backcountry please consider filling out a Mountain Information Network report.

Snowpack Summary

New snow continues to accumulate with southwest winds forming wind slabs on north and east aspects. New snow is resting on a variety of wind-affected surfaces and crusts with small surface hoar in places in the alpine. Below roughly 1700 m a widespread 5-10cm melt-freeze crust is present at or near the surface.

A concerning persistent weak layer of surface hoar and/or facets is 50-80 cm deep and exists on north facing alpine features.

Check out this MIN from our field team to learn more.

Weather Summary

Monday night

Cloudy with flurries bringing 5-10 cm of new snow. Strong southwest winds.

Tuesday

Mostly cloudy with continuing flurries bringing about 5 cm of new snow. Moderate to strong south winds. Treeline high temperatures around -7.

Wednesday

A mix of sun and cloud with flurries bringing less than 5 cm of new snow. Light to moderate southwest winds. Treeline high temperatures around -8.

Thursday

Cloudy with isolated flurries and a trace of new snow. Light northeast winds. Treeline high temperatures around -10.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Wind slabs are most reactive during their formation.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Persistent slabs have potential to pull back to lower angle terrain.
  • In times of uncertainty conservative terrain choices are our best defense.

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.