Avalanche Forecast

Issued: Dec 14th, 2022 4:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada zryan, Avalanche Canada

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Northerly winds have formed stiff wind slabs in unusual areas and at lower elevations than you might typically expect. These slabs are expected to bond poorly to the underlying crust.

Concern for buried weak layers continues to demand conservative terrain selection and good travel habits.

Summary

Confidence

Moderate

Avalanche Summary

During the storm last Friday, a natural avalanche cycle occurred, with natural storm slab avalanches up to size 2. Numerous skier-triggered storm slabs were reported in this time period as well. Notably, some explosive control produced persistent slab avalanches that failed on the mid-Nov crust down about 50cm and propagated around 50m wide.

Over the weekend, natural activity began to taper but human triggering remained likely! Many riders in the Squamish and Whistler area got surprised by size 1-2 slab avalanches. These slabs mainly occurred on wind-loaded slopes on north and west aspects in the alpine and treeline. Check out these MIN reports for examples (MIN1) (MIN2).

Looking forward to Thursday, northerly winds are expected to redistribute the surface snow into fresh wind slabs anywhere it remains loose and powdery. Keep in mind that small avalanches have the potential to 'step down' to deeply buried weak layers resulting in larger than expected avalanches.

Thank you for sharing your observations! Please keep posting to the MIN; it helps strengthen our information gathering.

Snowpack Summary

Surface: Large surface hoar growth has been observed in sheltered areas. A crust exists on solar aspects. Around 30 to 50 cm of recent snow, but also at or near the surface you can find wind-scoured, wind-pressed, and of course wind slabs.Upper-pack: The upper snowpack consists of 30-50 cm of settling snow. Below this, large surface hoar (up to 10 mm) has been observed mainly in shaded or sheltered areas. Mid-pack: 40-150 cm down is a late November crust, with soft facets above. This is likely the critical snowpack weakness. Professionals are concerned about the possibility of avalanches releasing at this deeper interface with the new snow load and warm temperatures.

Total snow depths remain low for early December with 90 to 140 cm at treeline and up to 200 cm in the alpine. Much of the below treeline elevation band is below the threshold for avalanches.

Weather Summary

Wednesday night

Clear with cloudy periods. Alpine temperatures drop to a low of -3 °C. Ridge wind 25 km/h gusting to 50 km/h from the northeast. Freezing level at valley bottom.

Thursday

Mainly sunny. Alpine temperatures reach a high of 1 °C. Ridge wind 25 km/h gusting to 55 km/h from the north. Freezing level rises to 1700 metres.

Friday

Sunny with an alpine temperature inversion. Alpine temperatures reach a high of 2 °C. Mostly light northerly ridge wind occasionally gusting to 45 km/h. Freezing level rises to 2500 metres.

Saturday

A mix of sun and cloud. Alpine temperatures reach a high of -4 °C. Ridge wind 20 km/h occasionally gusting to 45 km/h from the southwest. Freezing level at valley bottom.

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.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.

Problems

Wind Slabs

An icon showing Wind Slabs

Northerly winds are expected to form fresh, reactive wind slabs in the alpine and treeline. These slabs are expected to form on southerly aspects and may bond poorly to the underlying crust.

Wind slabs have the potential to step down to the mid-November weakness in the middle of the snowpack, resulting in large avalanches.

Aspects: East, South East, South, South West, West, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

Last week's storm buried a weak layer of surface hoar, which has been the culprit for several skier-triggered avalanches in the past week. This layer is now buried 40-70 cm down and is most likely to exist in sheltered and shaded locations.

Soft facets on a crust about halfway down into the snowpack may become more sensitive to triggering with the additional load from last week's storm and rising temperatures throughout this week. Small avalanches or large cornice falls could step down to this layer resulting in large, consequential avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Dec 15th, 2022 4:00PM