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Avalanche Forecast

Archived

Apr 29th, 2023–Apr 30th, 2023

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

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.

A high freezing level is destabilizing the snowpack, triggering numerous different avalanche problems. Check out the latest Forecasters' Blog for more information.

Confidence

Moderate

Avalanche Summary

We've seen widespread wet loose and cornice avalanche releases, of which some has stepped down to buried weak layers, producing very large avalanches. We expect this trend to continue. See here, here, and here for a couple examples.

Riders should expect wet loose avalanches and cornice failures during periods of warm air and rain. Avoiding steep slopes when the snow feels sloppy and avoiding cornice exposure are good travel habits.

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

Snowpack Summary

The snow surface is moist to mountain tops, which is unlikely to freeze overnight. Rain will keep the surface moist well into the alpine, but light snow may accumulate at the top of the highest peaks in the region.

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 are weakening with intense warming.

Weather Summary

An offshore low pressure system will bring cooler weather for Sunday, with associated rain and perhaps 5 to 10 cm of snow to the highest mountain tops above the freezing level of about 2500 m. The freezing level rises back to 3000 m on Monday with mostly cloudy skies but perhaps some sunny breaks. Tuesday is warm with mostly clear skies and a freezing level to 3700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid exposure to overhead avalanche terrain as temperatures increase.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
  • 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.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.

Problems

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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.