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Avalanche Forecast

Archived

Mar 6th, 2021–Mar 8th, 2021

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

Regions

Yukon.

When the highway to White Pass reopens adopt a cautious mindset while you figure out conditions. If you are headed to the Wheaton Valley, be alert to its weaker snowpack structure. Err on the side of more conservative low angle terrain.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

SATURDAY NIGHT: A few flurries, accumulation 1-3 cm, light west switching to north wind, alpine temperatures -10 C.

SUNDAY: Mainly cloudy with isolated flurries possible, light northeast wind, alpine temperatures a few degrees cooler around -12 C. 

MONDAY: Mainly cloudy with sunny breaks, light to moderate northwest wind, alpine temperatures around -13 C.

TUESDAY: A mix of sun and cloud, moderate southwest wind, alpine temperatures -8 C. 

Avalanche Summary

With the South Klondike Highway closed, for White Pass avalanche summary, read Wed March 03 forecast.

With recreational traffic diverted to places like the Wheaton, our field team did similar this week. They observed up to size 2.5 avalanches, especially on south facing slopes, starting high on ridges and rolling well into and through the trees. See a couple of MIN posts here and here.

The term 'Wheatonesque whumpfs' is worth holding onto. Remember that a whumpf is an avalanche that tried, with one key ingredient is missing -- slope angle. Whumpf the right terrain and you've converted it into the real thing, hopefully it's not rolling down ontop of you.

Snowpack Summary

For White Pass snowpack structure read Wed March 03 forecast.

With the South Klondike Highway closed lets talk about the Wheaton Valley snowpack. There is likely a crust that has formed on the surface on steeper sunny aspects with recent sunshine. The Wheaton's continental snowpack is the kind of thing you'd find around Jasper or Kananaskis Country. It's a weak snowpack dominated by sugary facets and depth hoar, the icing is either layers or a fat cap of harder cohesive slab. It's an untrustworthy structure that, in the old days, was compared to the crazy mother-in-law who lives in your basement and you never know when the relationship is going to go sideways. To re-phrase, it's an untrustworthy structure that requires really good terrain selection and travel habits, or a healthy dose of luck.

Terrain and Travel

  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.

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.