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Avalanche Forecast

Archived

Dec 13th, 2021–Dec 14th, 2021

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

Regions

North Rockies.

Wind slabs continue to be the primary concern on Tuesday. Due to recently shifting wind directions, slabs should be expected on all aspects in exposed terrain. 

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

An Arctic high pressure system is expected to be the dominant feature for most of the week bringing cold and dry conditions to the region.

Monday Overnight: Partly cloudy, moderate to strong NE-E winds, treeline temperature around -18 °C.

Tuesday: Mostly sunny, light to moderate variable winds, treeline high around -18 °C. 

Wednesday: A mix of sun and cloud, moderate SW winds, treeline high around -14 °C. 

Thursday: A mix of sun and cloud, moderate to strong NW winds, treeline high around -14 °C.

Avalanche Summary

An early report from Monday shows two natural size 2 wind slab avalanches on SW aspects at around 1700 m near Pine Pass. On Sunday, no new avalanches were reported. On Saturday, a report on social media suggests there was an human triggered avalanche in the old Azu area outside Powder King but details on the avalanche are very limited. A MIN report from Saturday describes a size 2.5 natural avalanche on a SE aspect near the Farm Cabin and this MIN report describes some natural wind slab avalanches in the Red Mountain area. 

On Tuesday, wind slabs are expected to remain the primary concern in the region. Newer wind slabs which formed on Monday from the NE winds will likely be the most reactive but the older wind slabs from the weekend are still expected to be reactive, especially in steep, unsupported terrain features. 

Snowpack Summary

On Friday and Saturday, 20-30 cm of new snow was reported along with strong winds from the southwest which formed highly reactive slabs in wind exposed terrain, primarily on north and east aspects. On Monday, the wind switched directions and has likely formed new wind slabs on south and west aspects. 

The mid and lower snowpack likely contains of a series of early season crusts which may had undergone some faceting. In the deeper snowpack areas of the region, these layers generally appear to have stabilized and gone dormant but they still may be reactive in isolated areas, especially places with a shallow snowpack. 

Snowpack depth at treeline typically ranges from 50-200 cm, with the shallower value mainly on the eastern side of the range. The alpine snowpack typically ranges from 150-200 cm. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be alert to conditions that change with elevation and wind exposure.

Problems

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.