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Avalanche Forecast

Archived

Jan 7th, 2022–Jan 8th, 2022

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

Regions

South Columbia.

Continue to make conservative terrain choices while the storm snow settles and stabilizes. Reactive slabs are still a concern for riders below ridgelines and around steep open slopes.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

The intense winter storm will ease off Friday night. A weak ridge of high pressure will strengthen over the Interior and generate strong outflow winds along with residual flurries for the weekend. A warm front is expected to invade the region Monday night, with widespread snow and significantly warmer temperatures. 

FRIDAY NIGHT: Snow 5 cm / Freezing level at valley bottom / Moderate west wind / Low of -15

SATURDAY: Flurries / 5-10 cm overnight / Freezing level at valley bottom / Moderate west wind peaking up to 60 km/h at night / High of -12

SUNDAY: Cloudy / Freezing level around 500 m/ Moderate to strong southwest wind / High of -10

MONDAY: Snow / Freezing level around 500 m / Moderate south wind / High of -5

Avalanche Summary

Widespread loose dry avalanches were observed on unsupported features at treeline and below during the storm. Storm snow was very reactive to riders, as they were able to easily trigger soft slabs avalanches up to size 1.5 within the new snow. 

The limited visibility in the alpine restricted observations on Thursday and Friday, but we suspect that a natural avalanche cycle occurred at night Thursday or early morning Friday. 

Although this layer has seen more activity in the south and east region (details and photos here) it remains a serious concern for the South Columbias region, particularly as the current storm is rolling in.

Snowpack Summary

The region received 30 to 40 cm low-density snow and consistent 50 km/h southerly wind since the start of the storm Thursday. This new snow is falling on a variety of surfaces, thin sun crust on solar aspects, isolated surface hoar at treeline on sheltered slopes, fresh wind slabs in lee alpine features at treeline and above or even previous storm snow (20-50 cm) from the last weekend's storm.

We're actively monitoring the early December crust. In some places, it's scoured and on the surface, while in wind-loaded terrain features it can be found as deep as 150 cm below the surface. It consists of faceted grains above a bulletproof crust formed by the Atmospheric Rivers of early December. Avalanches failing on this interface have the potential to be very large. 

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Be aware of the potential for human triggerable storm slabs at lower elevations, even on small features.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.