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Avalanche Forecast

Archived

Mar 8th, 2021–Mar 9th, 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

Purcells.

Watch out on recently wind affected slopes and slopes experiencing direct sunshine. Buried weak layers in the northern part of the region may still be reactive.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

MONDAY NIGHT: Clear and cold, with alpine temperatures dipping to around -12 C.

TUESDAY: A clear start with clouds increasing through the day. Light variable winds. Alpine high temperature -3 C. Freezing level 1400 m.

WEDNESDAY: Light snow, 2-5 cm. Light to moderate southwesterly winds. Alpine high temperature -3 C. Freezing level 1400 m.

THURSDAY: Isolated flurries. Light to moderate westerly winds. Alpine High temperature -3 C. Freezing level 1200 m.

Avalanche Summary

On Sunday, only small loose dry avalanches were noted in steep terrain.

On Saturday, one size 2 wind slab on an east aspect and one size 1.5 cornice release on a northeast aspect were noted, both in the alpine.

Last week there were several notable reports of large human triggered persistent slab avalanches in the Dogtooth Range and Quartz Creek area. See these MIN reports here and here. The likelihood of triggering on these layers has since gone down, but it's still worth considering the potential for a similar release to occur.

Snowpack Summary

Dry soft snow can be found on shaded aspects above around 1500 m. On south-facing slopes and at lower elevations expect crusty snow in the morning and soft moist snow in the afternoon. Recent wind slabs and cornices still pose a hazard close to steep ridgelines.

Persistent weak layers were reactive last week, particularly in the northern end of the Purcells. The layers of concern are a buried layer of surface hoar that formed in late January is 30-60 cm deep and an older surface hoar layer is 50-100 cm deep at treeline. These layers may exist as a combination of facets and crusts at other elevations. Recent assessments indicate the chance of triggering these layers has reduced, but writing them off completely is probably premature.

Shallow rocky areas where the snowpack is thin likely have sugary facets acting as a weak layer at the base of the snowpack.

Terrain and Travel

  • Be carefull around freshly wind loaded features.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.