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Avalanche Forecast

Archived

Apr 12th, 2021–Apr 13th, 2021

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

Regions

North Columbia.

It's going to be a sunny and warm day with freezing levels rising to 1900 m. Cornices are big and fragile and a hazard on their own if they fail. Be alert to changing conditions on sun exposed slopes during the heat of the day, especially if the snow becomes moist or wet.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

A ridge of high pressure over the province brings sunny, dry weather. Freezing levels are forecast to steadily rise through the week.

Monday night: Clear, moderate easterly wind, alpine low -16 C, freezing level at valley bottom. 

Tuesday: Sunny, light to moderate northeast wind, alpine high +3 C, freezing level 1900 m.

Wednesday: Mostly sunny, moderate to strong northeast wind, alpine high +6 C, freezing level 2600 m.

Thursday: Sunny, moderate east wind, alpine high +8 C, freezing level 2700 m.

Avalanche Summary

Wind slabs have shown quite limited reactivity over the weekend, a few natural and ski cut size 1-1.5 were observed on Saturday. On Friday, most activity in the recent snow has been limited to size 1 loose snow avalanches. One size 2 was reported.

A couple of natural cornice failures size 2.5 observed on Sunday did not trigger slabs on slopes below. 

Neighboring Glacier National Park reported a few very large (size 3-4) glide slab releases on Thursday. Glide slabs are hard to predict and can release at any time so it is important to avoid slopes with glide cracks.

Snowpack Summary

The 20-30 cm of recent snow sits on a series of melt-freeze crusts on all aspects below 1900 m and southerly aspects to mountain top. The recent snow is going through a diurnal cycle becoming moist during the daytime and refreezing overnight. Reports indicate that this snow might not be bonding well to the underlying crust. On North aspects in the alpine, the recent snow sits on dry wintery snow surfaces and possibly surface hoar on wind-sheltered slopes.

The recent warm weather is expected to have helped old persistent weak layers heal, including a few crusts buried over the last month as well as a facet layer 150 cm deep from the mid-February cold snap.

Terrain and Travel

  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
  • Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.

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.

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.

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.