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Avalanche Forecast

Archived

Apr 25th, 2023–Apr 26th, 2023

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

Regions

Sea To Sky, South Coast Inland, Brandywine, Garibaldi, Homathko, Spearhead, Tantalus, Sasquatch, Sky Pilot, Birkenhead, Coquihalla, Duffey, Harrison-Fraser, Manning, Skagit, South Chilcotin, Stein, Taseko.

Wintry conditions are found in the alpine, whereas spring-like problems are prominent at lower elevations. Travel cautiously and be aware of the various avalanche problems you could come across.

Confidence

Moderate

Avalanche Summary

Many small to large (size 1 to 2) wet loose avalanches were observed over the weekend and on Monday, generally occurring out of steep alpine terrain. We expect to see similar avalanches in the coming days during periods of rain, sunny skies and an increasing freezing level. Small wind slabs may be possible to trigger in steep leeward alpine terrain on Wednesday.

The likelihood of seeing very large avalanches releasing on the buried weak layer described in the Snowpack Summary will increase with each day of warming this week. This is particularly true for days without an overnight refreeze. Humans are most likely to trigger this layer in steep and rocky slopes where the snowpack is relatively thin.

Also use plenty of caution along alpine ridges, where cornices are likely large and weakening.

Snowpack Summary

Rain will moisten the snow surface up to about 1800 m. Snow will accumulate at alpine elevations, which may be pushed into small wind slabs in lee terrain features with southwest wind.

The middle of the snowpack is consolidated with various layers of moist snow, hard snow, and melt-freeze crusts.

A layer of weak faceted grains is found near the base of the snowpack at treeline and alpine elevations.

Cornices are large and looming at this time of year and will weaken with daytime warming.

Weather Summary

Tuesday Night

Increasing clouds with no precipitation, 20 to 40 km/h southwest wind, treeline temperature 0 °C, freezing level 2000 m.

Wednesday

Cloudy with light snow or rain, accumulation 2 to 10 cm above the rain-snow line, 30 to 50 km/h southwest wind, treeline temperature 0 °C, freezing level 2000 m.

Thursday

Mostly sunny with no precipitation, 10 to 20 km/h variable wind, treeline temperature 5 °C, freezing level rising to 3400 m.

Friday

Sunny with no precipitation, 10 km/h southeast wind, treeline temperature 10 °C, freezing level 3700 m.

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.
  • Cornice failures could trigger very large and destructive avalanches.
  • Carefully evaluate steep lines for wind slabs.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.

Problems

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.