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Avalanche Forecast

Archived

Feb 23rd, 2023–Feb 24th, 2023

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

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

Wind slabs are the main concern. Keep in mind you may find them on a variety of aspects with recent shifting winds.

Confidence

Moderate

Avalanche Summary

Reports from Thursday confirm a natural avalanche cycle occurred in the Coquihalla area Monday night and Tuesday. Avalanches were reported as size 2-3 wind slabs, storm slabs and persistent slabs on northwest, northeast and southeast aspects in the alpine and treeline elevation bands. The persistent slab avalanches were suspected to have run on the facet/crust layer buried in mid-January (outlined in the avalanche problem section).

Please continue to post your reports and photos to the Mountain Information Network.

Snowpack Summary

Northeasterly winds have redistributed 20-40 cm of new snow and formed stiff wind slabs in exposed areas. In sheltered areas, surface faceting due to cold temperatures and/or soft surface snow may remain.

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 has been reactive during the storm Tuesday night and Wednesday this week. 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 decreases significantly below 1500 m.

Weather Summary

Thursday night

Clear periods. Alpine temperatures drop to a low of -19 °C. Ridge wind northeast 15 km/h. Freezing level at valley bottom.

Friday

Sunny with cloudy periods. Alpine temperatures reach a high of -9 °C. Ridge wind southwest 10-25 km/h. Freezing level at valley bottom.

Saturday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -6 °C. Ridge wind southwest 20 km/h gusting to 40 km/h. Freezing level at valley bottom.

Sunday

Cloudy with snowfall, 5-15 cm of accumulation. Alpine temperatures reach a high of -3 °C. Ridge wind southwest 30 km/h gusting to 75 km/h. Freezing level: 700 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.