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Avalanche Forecast

Archived

Nov 26th, 2022–Nov 27th, 2022

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 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

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Friday's storm built fresh soft slabs which contributed to the persistent slabs that were already overlying a weak base.

With many natural avalanches observed in the alpine Saturday, expect the avalanche hazard to remain elevated through Monday as another dose of wind and snow is on track to arrive Saturday evening.

Confidence

Moderate

Avalanche Summary

A forecasting team to the 93N today observed many new avalanches in alpine terrain. Several sz 1-1.5 persistent slabs around 40cm deep were seen below steep rock features that had apparently been triggered by the more widespread loose dry activity in the past 24 hrs. Elevated winds remained with continued loose dry events observed to be spilling out of extreme terrain such as gullies on Bow Peak. Both SSV and LLSA reported dealing with thin soft slabs and seeing a couple of sz 1-2 persistent slabs in closed or nearby backcountry terrain.

Snowpack Summary

10 to15cm of new snow arrived with strong to extreme SW-W winds over the past 36 hours. Freezing levels have returned to valley bottom but were higher in eastern areas through Friday : snow accumulations taper with elevation. Mild temperatures and wind have promoted new slab development. The snowpack below these slabs is a mix of facets, some spotty surface hoar, and sun crust on steep south aspects. There is even some classic Rockies depth hoar forming at the base in thinner areas. 40-80 cm of total snow exists at treeline throughout the region, with up to 120 cm in loaded alpine features.

Weather Summary

Another cold front will pass through the region Saturday overnight brining 5-10 cm of snow favoring western and northern areas. Winds will shift to the SW and increase to 60km/h.. Sunday a few flurries will remain as winds weaken to 40km/h and shift NW. A ridge will build through Sunday with winds shifting N and decreasing to 20km/h overnight.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.