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Avalanche Forecast

Archived

Feb 27th, 2023–Feb 28th, 2023

Alpine
Natural avalanches possible, human triggered probable.
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 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.

Regions

Sea To Sky, Brandywine, Garibaldi, Homathko, Powell River, Spearhead, Tantalus, Sasquatch.

Be particularly cautious in wind-loaded areas and continue to make conservative terrain choices while the storm snow settles and stabilizes.

Confidence

Moderate

Avalanche Summary

During the storm on Sunday, numerous natural and human-triggered storm slabs up to size 2 were reported from all aspects and elevations. Observations were limited due to visibility, but we suspect a natural cycle occurred in alpine terrain.

Looking forward to Tuesday, human-triggered storm slabs remain likely, especially in wind-loaded areas. Storm slab reactivity is expected to persist for longer than is typical due to the weak surface they are sitting on.

For a deeper dive into conditions leading up to last weekend's storm, check out this awesome South Coast Conditions Report posted by Zenith Guides.

Snowpack Summary

An additional 5-10 cm will accumulate throughout the day on top of Saturday night's 20-50 cm of new snow down to valley bottom. In some areas, this new snow has bonded poorly to the underlying surface consisting of stiff wind slabs and near-surface faceting formed by recent wind and cold temperatures.

There are two crusts with facets sitting above, which are buried in the snowpack down 60-180cm in the alpine and treeline elevation bands. These crust/facet layers have been responsible for a few large avalanches in the past 2 weeks in the Brandywine and Pemberton Icefield areas.

The remainder of the mid and lower snowpack is well-settled, strong, and consolidated.

Weather Summary

Monday night

Cloudy with clear periods and isolated flurries, up to 5 cm of accumulation. Alpine temperatures drop to a low of -10 °C. Light ridge wind from the southeast. Freezing level at valley bottom.

Tuesday

Cloudy with flurries, 5-10 cm of accumulation. Alpine temperatures reach a high of -8 °C. Ridge wind light southeast. Freezing level at valley bottom.

Wednesday

Cloudy with sunny periods and isolated flurries. Alpine temperatures reach a high of -9 °C. Ridge wind southwest 15 km/h gusting to 40 km/h. Freezing level at valley bottom.

Thursday

Cloudy with snowfall, 5-15 cm of accumulation. Alpine temperatures reach a high of -7 °C. Ridge wind southwest 30 km/h gusting to 80 km/h. Freezing level 900 meters.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Carefully monitor the bond between the new snow and old surface.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Problems

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.

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.