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Avalanche Forecast

Archived

Jan 30th, 2022–Jan 31st, 2022

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

Regions

North Columbia.

Expect touchy avalanche conditions at all elevations. Wind-kissed storm slabs have potential to propagate widely and loose dry avalanches are likely on steep, sheltered slopes. Stick to low consequence terrain.

Confidence

High -

Weather Forecast

The Monashees will see highest snowfall amounts out of this storm.

Sunday night: Snowfall 10-25 cm, moderate SW wind, treeline temperature around -7 °C.

Monday: Flurries up to 5 cm, light to moderate NW wind, treeline high around -9 °C.

Tuesday: Mostly cloudy with scattered flurries, moderate NW wind, treeline high around -13 °C.

Wednesday: Mostly cloudy, light wind, treeline high around -18 °C.

Avalanche Summary

The theme during the dry spell last week was large cornice failures and wind slab avalanches size 2-3 on north to east aspects in the alpine. On Friday, wind slabs were reactive to explosives up to size 3 and skier traffic up to size 1. Dry loose avalanches were also observed up to size 2.

On Tuesday, a natural size 1.5 persistent slab was reported on an E aspect at 1900 m in the Monashees north of Revelstoke, likely failing on one of the surface hoar or crust layers 30-45 cm deep.

Deep persistent slab activity on the early December facet/crust layer slowed down during the dry spell. Most recently, two naturals were reported on Monday, size 2.5-3. Between January 20 and 23, numerous very large (size 2.5-4.5) deep persistent slab avalanches occurred on this layer, typically 100-150 cm deep.

Snowpack Summary

New snow continues to accumulate over faceting wind affected surfaces in the alpine, a melt-freeze crust on steep solar aspects & low elevations and a widespread layer of large surface hoar crystals, especially prominent in shady, wind sheltered areas at elevations near the top of the previous valley fog layer (1200-2000 m). New snow is expected to adhere poorly at this interface.

There are three prominent layers in the upper snowpack which have been largely dormant during the dry spell but may become reactive with new snow loads. These include a layer of surface hoar down 20-30 cm, a layer of facets and/or surface hoar from early January down around 40-60 cm, and a thick layer of facets from the end of December down close to 1 m.

The primary weak layer that remains a widespread concern across the Columbia Mountains is a deeply buried crust/facet layer that formed in early December. It is typically down 100-180 cm, but as deep as 250 cm in wind-loaded terrain. This layer is likely to plague our snowpack for the remainder of the season and will be a low probability but extremely high consequence result if triggered. Check out our latest forecaster blog on the crust that never dies.

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • The trees are not a safe haven right now.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Good day to make conservative terrain choices.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.