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Avalanche Forecast

Archived

May 5th, 2023–May 6th, 2023

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

Regions

Cariboos, Kootenay Boundary, Lizard-Flathead, North Columbia, North Rockies, Purcells, South Columbia, South Rockies, Glacier, Blue River, Clearwater, McBride, Premier, Quesnel, Sugarbowl, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Akamina, Flathead, Lizard, Clemina, Esplanade, Jordan, North Monashee, North Selkirk, Shuswap, Kakwa, McGregor, Pine Pass, Renshaw, Robson, Tumbler, Dogtooth, East Purcell, Moyie, St. Mary, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan, Bull, Crowsnest North, Crowsnest South, Elkford East, Elkford West.

The snowpack needs time to adjust to last week's intense warming. Be aware of the various avalanche problems that still exist.

Confidence

Moderate

Avalanche Summary

An avalanche cycle of large to very large (size 2 to 4) wet loose and slab avalanches, cornice failures, and deep persistent slab avalanches occurred over much of the region within the past two weeks. The likelihood of triggering may decrease while the snowpack experiences lower freezing levels and cloudy skies.

Snowpack Summary

A moist snow surface is expected below the rain-snow line, which will freeze into a melt-freeze crust overnight. Any snow that accumulates in the high alpine will build onto a hard melt-freeze crust.

The intense heat from the past two weeks moistened the snowpack. The warming reawakened weak layers, including weak snow above crusts buried in late March (50 to 100 cm deep) and the weak basal facets found at the bottom of the snowpack.

The snowpack is quickly diminishing below treeline, but large avalanches could release at higher elevations and run into valley bottoms.

Weather Summary

Saturday sees a freezing level decline to around 2500 m by late afternoon with mostly cloudy skies and periods of light rain. Sunday and Monday's freezing level is between 2000 m and 2500 m with mostly cloudy skies and periods of rain or snow in the high alpine.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Watch for fresh storm slabs building throughout the day.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Avoid steep slopes when air temperatures are warm, it is raining, or solar radiation is strong.
  • Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.

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.

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.

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.