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Avalanche Forecast

Archived

Feb 15th, 2023–Feb 16th, 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 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.

Expect to find deep and touchy wind slabs that could form large avalanches. Persistent slabs may also linger in specific terrain. Conservative terrain travel is recommended.

Confidence

Moderate

Avalanche Summary

We received reports of numerous small to large (size 1 to 2) wind slabs triggered by riders and naturally in lee terrain features over the past few days. Slabs on Tuesday were 30 to 50 cm deep around treeline and propagated widely.

Check out this MIN from our field team that discusses the wind slab problem in greater detail.

On Friday, a large avalanche was triggered by riders, likely releasing on the weak layer described in the Snowpack Summary. See this MIN for details and photos, highlighting the propagation potential and high consequence nature of this layer.

Snowpack Summary

Up to 80cm of storm snow has been redistributed into wind slabs on north and east aspects. Southerly slopes are generally scoured or wind pressed. In sheltered areas the above mentioned snow is still soft and likely makes for decent riding.

A hard melt-freeze crust that extends up to about 1700 m is now on the snow surface in wind-exposed terrain and otherwise buried about 50 to 80 cm in wind-loaded terrain. The crust appears to be bonding to the snowpack.

A weak layer of surface hoar and facets may be buried about 80 to 120 cm deep on north to east aspects in alpine and upper treeline elevations. The layer may rest on a harder melt-freeze crust. Where preserved, this layer has shown to have very high propagation potential and capable of producing large avalanches hundreds of metres wide.

Weather Summary

Wednesday Night

Cloudy with a few centimeters of new snow expected. Light to moderate southwest wind and a low of -7 at 1500m.

Thursday

Cloudy with light flurries bringing a few centimeters of new snow. Light to moderate southwest winds and a high of -7 at 1500m.

Friday

Stormy with up to 10cm of new snow expected. Moderate to strong southwest winds and a high of -6 at 1500m.

Saturday

Cloudy with light flurries bringing a trace of new snow. Moderate to strong southwest winds and a high of -6 at 1500m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for areas of hard wind slab on alpine features.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • The best and safest riding will be on slopes that have soft snow without any slab properties.
  • Remote triggering is a big concern, be aware of the potential for wide propagations and large, destructive avalanches at all elevations.

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.