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Avalanche Forecast

Archived

Feb 27th, 2023–Feb 28th, 2023

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.
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.

Storm slabs may remain sensitive to human-triggering, particularly in wind-loaded areas.

Take a cautious approach and investigate the bond between the new snow and the old surface before comitting to your line.

Confidence

Moderate

Avalanche Summary

Observations have been limited throughout the storm last weekend. On Monday, one size 1.5 natural storm slab was observed from a distance on a steep treeline convex roll.

Looking forward to Tuesday, human-triggered storm slabs remain likely, especially in wind-loaded areas. Storm slab reactivity is expected to persist for longer than is typical due to the weak surface they are sitting on.

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

Snowpack Summary

An additional 5-10 cm will accumulate throughout the day. This overlies last weekend's 15-30 cm of new snow. In some areas, this new snow has bonded poorly to the underlying surface, consisting of stiff wind slabs and near-surface faceting formed by recent wind and 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 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

Monday night

Clear periods. Alpine temperatures drop to a low of -8 °C. Ridge wind light from the south. Freezing level at valley bottom.

Tuesday

Flurries in the afternoon, trace to 10 cm of accumulation. Alpine temperatures reach a high of -2 °C. Light variable ridge wind. Freezing level 600 meters.

Wednesday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -5 °C. Ridge wind southwest 15 km/h gusting to 45 km/h. Freezing level 500 meters.

Thursday

Cloudy with snowfall, 5-15 cm of accumulation. Alpine temperatures reach a high of -2 °C. Ridge wind southwest 30 km/h to 60 km/h. Freezing level 800 meters.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Carefully monitor the bond between the new snow and old surface.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.