Avalanche Forecast

Archived

Apr 22nd, 2021–Apr 23rd, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells.

Be careful around cornices and watch for new snow forming isolated wind slabs in the alpine.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Thursday night: Partly cloudy with isolated flurries up to 10 cm in the southwest of the region, light wind, alpine temperature near -7, freezing level near valley bottom.

Friday: Mostly cloudy, light to moderate northwest wind, alpine high near -3, freezing level 1900 m.

Saturday: Flurries up to 5 cm, light wind, alpine high near -4, freezing level 1700 m.

Sunday: Around 10 cm new snow, moderate to strong southwest wind, alpine high near -3, freezing level 1700 m.

Avalanche Summary

Warm temperatures last week resulted in widespread wet avalanche activity, primarily on sun-exposed slopes. Most of the activity was size 1-2 wet loose avalanches, but a few larger and destructive wet slab avalanches were reported near the Bugaboos on Saturday and near Golden on Monday. Some large cornice falls were also observed.

The cooling trend will make wet avalanches problems less likely in the coming days, making isolated wind slabs and cornice falls the primary concern.

Snowpack Summary

The upper snowpack has undergone multiple melt-freeze cycles and is now crusty and refrozen in the cooler temperatures. Dry snow may still be found on northerly aspects above roughly 2300 m. We suspect older weak layers have gone inactive as the weather patterns over the past month have been favourable for strengthening the snowpack.

Terrain and Travel

When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
Wind slabs may be poorly bonded to the underlying crust.
Watch for unstable snow on specific terrain features, especially when the snow is moist or wet.

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.

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.