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Avalanche Forecast

Archived

Feb 4th, 2022–Feb 5th, 2022

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

Regions

South Columbia.

The recent snow is loading a buried weak layer. Given the uncertainty on where exactly this layer may be buried and how the recent snow will influence it, your best bet is to avoid consequential avalanche terrain and give it some time.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm, 20 to 40 km/h southwest wind, alpine temperature -6 C.

SATURDAY: Cloudy with snowfall, accumulation 2 to 5 cm, 20 to 40 km/h west wind, alpine temperature -6 C, freezing level rising to 1300 m.

SUNDAY: Mix of sun and cloud with no precipitation, 20 to 30 km/h southwest wind, alpine temperature -1 C, freezing level rising to 2000 m.

MONDAY: Cloudy with snowfall, accumulation 5 cm, 30 km/h southwest wind, alpine temperature -4 C, freezing level 1400 m.

Avalanche Summary

May storm and wind slabs were triggered by riders on Thursday to add to the many avalanches observed in the previous few days. Most of the storm slabs released on the surface hoar layer described in the Snowpack Summary, often occurring between around 1600 and 2200 m on all aspects except due south. Read this MIN for a detailed description of a skier-triggered avalanche in the south of the region -- thank you for the detailed report.

Natural and rider-triggered avalanche activity is expected to spike Friday night into Saturday morning during the peak of the storm. Large avalanches are expected to be easily triggered by riders on Saturday in areas where the buried surface hoar described in the Snowpack Summary exists. Avoidance of avalanche terrain, particularly where the surface hoar may exist, is your best bet for having a safe day.

Snowpack Summary

Storm totals may reach 20 to 30 cm by Saturday with locally higher amounts possible. The snow has likely formed new storm slabs in areas sheltered from the wind and wind slabs in exposed terrain at higher elevations from strong south to southwest wind. 

The snow is loading a weak layer of surface hoar crystals 5 to 15 mm in size. Forecast warming may also increase the likelihood of triggering a slab. The layer may be around 40 to 80 cm deep, which is a prime depth for human triggering. The layer is most prominent in areas sheltered from the wind. Example terrain features to treat as suspect include the lee side of protected ridges, openings in the trees, cut blocks, and burns. The layer may not exist on steep sun-exposed slopes, where a melt-freeze crust may be found instead.

The facet/crust layer that formed in early December is buried around 100 to 200 cm. The last reported avalanche was on January 28 in the north of the region. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.

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.

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.