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Avalanche Forecast

Archived

Feb 23rd, 2024–Feb 24th, 2024

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

Regions

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

If I had to pick one region in the southwest to trigger a destructive persistent slab, this would be it. The problems are in play, new snow and wind will add to their reactivity and consequence.

Confidence

High

Avalanche Summary

Wednesday's reports showed 15-20 cm of new snow becoming reactive with warming and yielding many skier-triggered avalanches to size 1 and naturals to size 2 in the MacGillivray Pass area. At least one size 2 ran on our early February facet/crust layer.

Reports from Thursday support these observations of instability with local operators noting widespread cracking of storm snow above the early February facets as well as small ski cuts stepping down to the crust below.

Snowpack Summary

Up to about 10 cm of new snow should fall in the region through Saturday. It will bury sun crust on solar aspects but mainly add to 15 - 20 cm already overlying previous surfaces that include crust on south aspects and lower elevations, faceted snow and/or small surface hoar in sheltered features, and previously wind-affected surfaces in the open.

Roughly 40 - 50 cm of snow now sits above a widespread crust from late January. Weak grains like facets or more isolated surface hoar may be found above this crust. Especially with the load above it increasing, this problematic layering remains a concern with ample recent avalanche activity and snowpack tests showing its potential.

Weather Summary

Friday night

Cloudy with flurries bringing less than 5 cm of new snow. 20 - 30 km/h southwest alpine wind. Freezing level falling to valley bottom.

Saturday

Cloudy with scattered flurries bringing less than 5 cm of new snow. 20 to 30 km/h southwest alpine wind. Treeline temperature -2 °C with freezing level to 1500 m.

Sunday

Cloudy with flurries bringing 5 - 15 cm of new snow, including overnight amounts. 40-50 km/h southwest alpine winds. Treeline temperature -3 °C with freezing level to 1500 m, falling sharply in late afternoon.

Monday

A mix of sun and cloud with isolated flurries. 10-15 km/h southwest alpine wind. Treeline temperature -5 °C with freezing level at valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs are most reactive during their formation.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.