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Avalanche Forecast

Archived

Mar 1st, 2023–Mar 2nd, 2023

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

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

Another 25 cm of new snow is forecast to blanket the region overnight. Natural and human-triggered avalanche activity is expected on Thursday.

Confidence

Moderate

Avalanche Summary

On Tuesday, a few wet loose avalanches up to size 1 were reported below treeline.

On Monday, one size 1.5 natural storm slab was observed from a distance on a steep treeline convex roll, and a natural glide slab released size 2 from a south aspect at 1600 m and ran 300 m in length.

Looking forward to Thursday, natural and human-triggered storm slabs are likely. Storm slab reactivity is expected to persist for longer than is typical due to the weak surface they are sitting on.

Snowpack Summary

25 + cm of new snow and strong winds overnight Wednesday will add to the 30 cm of settling storm snow that fell last weekend. The new snow may have a poor bond to the underlying stiff wind slabs and faceted snow formed by recent cold temperatures.

A melt-freeze crust formed in mid-January is buried up to 90-140 cm deep. In some areas, small faceted crystals can be found above the crust. This layer was reactive a week ago. The snow below this layer is well consolidated.

Snowpack depths are just below seasonal averages. Total amounts range from 150 to 300 cm at treeline, but decrease significantly below 1500 m.

Weather Summary

Wednesday Night

New snow 10-20 cm. Alpine temperatures -7°C. Ridge wind southwest 30 to 70 km/h. Freezing level valley bottom.

Thursday

Snow up to 10-20 cm. Alpine temperatures -4 °C. Southwest wind 30 to 75 km/h. Freezing level 600 m.

Friday

Snow amounts 10 cm. Ridgetop wind 20 to 65 km/h from the southwest. Alpine temperatures -5°C. Freezing level 600 m.

Saturday

A mix of sun and cloud with isolated flurries. Alpine temperatures near -5 °C. Ridge wind northeast 15 km/h. Freezing level 700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid all avalanche terrain during periods of heavy snowfall.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Closely monitor how the new snow is bonding to the crust.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.