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Avalanche Forecast

Archived

Feb 7th, 2023–Feb 8th, 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 possible, human triggered probable.
Below Treeline
Below Threshold.

Regions

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

Tuesday's observations confirm all those flurries and winds have indeed been scattering reactive wind slabs across alpine terrain, with some releasing naturally. Expect more of the same for Wednesday, with a continued chance of wind slab releases triggering a deeper snowpack layer to create larger, more destructive avalanches.

Confidence

High

Avalanche Summary

With the field team back in White Pass we received preliminary observations on Tuesday of a small scale natural wind slab avalanche cycle as a result of recent snowfall meeting with elevated winds, most recently from the west. Slab formation and releases appear to have been limited to alpine terrain thus far. No new persistent slab avalanches have been reported yet.

New surface instabilities aside, 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 share your observations to the Mountain Information Network!

Snowpack Summary

Light new snow amounts continue to accumulate with southwest winds forming wind slabs on north and especially east aspects in the alpine.

As of Tuesday these light amounts added up to about 20-30 cm now resting on a variety of wind-affected surfaces and crusts, small surface hoar in places in the alpine, and a widespread 5-10 cm melt-freeze crust below roughly 1700 m.

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

Tuesday night

Cloudy with flurries bringing 5-10 cm of new snow. Light to moderate southwest winds.

Wednesday

A mix of sun and cloud with easing flurries bringing up to 5 cm of new snow. Light to moderate southwest winds, increasing over the day. Treeline high temperatures around -8.

Thursday

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

Friday

Clear before clouding over midday. Winds ramping up to strong southwest. Treeline high temperatures around -9.

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.