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Avalanche Forecast

Archived

Dec 16th, 2022–Dec 17th, 2022

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

Purcells, Dogtooth, East Purcell.

As the temperatures drop over the next 48 hours you should be planning on dialing things back. Even a small accident can have big consequences with cold temps and short days.

We have uncertainty around the reactivity of a buried weak layer that produced large rider-triggered avalanches last weekend. Read our latest blog for advice on how to manage a persistent slab problem.

Confidence

Moderate

Avalanche Summary

On Thursday explosive control produced wind slab avalanches up to size 1.5 on north aspects.

Persistent slab activity has died down over the past couple days but over the last weekend the mid November layer was sensitive to rider triggering.

In the neighboring central Columbia and Kootenay Boundary regions, where it is buried deeper, this layer has produced Larger rider-triggered avalanches. Unfortunately, more likely than not, this is a sign of what is to come for the Purcells.

Snowpack Summary

Variable surfaces range from hard old wind slabs in exposed features at upper elevations to soft, unconsolidated facets in sheltered areas. As the winds shift to the northwest new wind slabs could form on southerly and easterly aspects.

A concerning weak layer composed of surface hoar, facets and/or a crust that formed in mid November is now buried 15-40 cm deep. Avalanche activity has been observed on this layer and is expected to continue as the overlying snow takes on more slab character due to settlement, wind and additional snow load.

Alpine snowpack distribution is variable, with depths ranging from 40 to 140 cm.

Weather Summary

Friday Night

Cloudy with the possibility of light flurries bringing trace amounts of new snow. Moderate westerly winds with a low of -15 at 1800m.

Saturday

Scattered flurries bringing up to 5cm of new snow. Light to moderate westerly wind. High of -14 at 1800m.

Sunday

Scattered flurries bringing up to 5cm of new snow. Light to moderate southerly wind. High of -18 at 1800m.

Monday

A mix of sun and cloud with no new snow expected. Light southwest winds and a high of -22 at 1800m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • In times of uncertainty conservative terrain choices are our best defense.

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.