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Avalanche Forecast

Archived

Mar 20th, 2022–Mar 21st, 2022

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

Regions

Northwest Inland.

Watch for wind slabs at upper elevations and keep in mind a recently buried weak layer remains triggerable around treeline.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Sunday night: Cloudy. Up to 5 cm new snow. Moderate southwest wind. Alpine low around-5 °C.

Monday: Cloudy with flurries bringing a trace. Moderate southwest wind. Alpine high around -2 °C. Freezing level rising to 1500 m. 

Tuesday: Snowfall 10-20 cm. Strong southwest wind. Alpine high around -1 °C. Freezing level 1700 m. 

Tuesday: Snowfall 5-15 cm. Moderate southwest wind. Alpine high around -6 °C. Freezing level 1000 m. 

Avalanche Summary

Most recent avalanche observations have been small wind slabs, and loose dry in steep terrain.

Persistent slab avalanches on a weak layer of surface hoar crystals buried in late February have surprised a few people in the last week with quickly propagating accidental and remote triggers. The layer has been most active on north-northeast aspects between 1200 and 1600 m in areas north of Hazelton.

Snowpack Summary

15-30 cm of recent snow has been redistributed into wind slabs in wind exposed terrain. This snow sits over a crust on solar aspects and below 1700 m. Some operations have reported surface hoar in this layer on sheltered north aspects. Those specific locations could be of increasing concern as the load of snow above them increases.

Around 30-45 cm deep, a surface hoar layer buried in late February is preserved in wind sheltered features at treeline and low alpine elevations. Recent snowpack tests and avalanche observations suggest that weak spots on this layer are hard to find, but the resulting avalanches will be surprisingly large if you trigger them.

The thick mid-February crust is now buried 50-80 cm deep, and in terrain where it is topped by a layer of loose, sugary facets, it could be possible to trigger with very large loads such as avalanches in motion or cornice falls.

The lower snowpack is well protected by the mid-February crust, and triggering avalanches below this layer is unlikely at this time. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Caution around convexities or sharp changes in terrain.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.

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.