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Avalanche Forecast

Archived

Apr 20th, 2023–Apr 21st, 2023

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

South Coast Inland, Birkenhead, Duffey, South Chilcotin, Stein, Taseko.

Assess for wind slabs in steep terrain at higher elevations. Small avalanches could step down to a buried layer and form large avalanches.

Confidence

Moderate

Avalanche Summary

Riders triggered a few wind slabs in steep leeward terrain on Wednesday (e.g., as seen here and here). They were 10 to 30 cm deep, on west to northwest aspects, and varied between about 2200 m and 2700 m in elevation.

The most recent avalanches on the facet layer described in the Snowpack Summary occurred about a week ago (e.g., this MIN).

Loong forward, we expect that riders could trigger wind slabs in steep lee terrain features at treeline and alpine elevations.

Snowpack Summary

Some new snow and southwest wind may form new wind slabs in lee terrain features at higher elevations. These slabs will build onto lingering 10 to 30 cm thick wind slabs that formed earlier this week. Underneath these wind slabs are a hard melt-freeze crust found on all aspects up to 1700 m and to mountain tops on southerly slopes or dry faceted snow on shaded aspects at high elevations.

A layer of facets and a crust from early April is buried up to 60 cm at treeline and alpine elevations. There's uncertainty in how this layer is bonding, but it was the culprit of many large avalanches around April 12.

The base of the snowpack remains faceted and weak. We haven't received any notes of recent avalanche activity on this layer, but the concern remains for steep and rocky slopes with a thin snowpack.

Cornices are large and looming at this time of year.

Weather Summary

Thursday Night

Cloudy with snowfall, accumulation 5 cm, 20 to 30 km/h south wind, treeline temperature -7 °C, freezing level 1000 m.

Friday

Early-morning sun and afternoon clouds with no precipitation, 10 km/h southwest wind, treeline temperature -4 °C, freezing level 1500 m.

Saturday

Cloudy with isolated snowfall, trace accumulation, 20 to 40 km/h southwest wind, treeline temperature -2 °C, freezing level 1700 m.

Sunday

Cloudy with snowfall, accumulation 5 cm, 20 to 40 km/h southwest wind, treeline temperature -2 °C, freezing level 1700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Carefully evaluate steep lines for wind slabs.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.