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Avalanche Forecast

Archived

Mar 11th, 2023–Mar 12th, 2023

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

Regions

Little Yoho.

While these deeper snowpack zones seem to be a bit better than the rest of the forecasting region, concern remains for the persistent weak layers to be human triggered from shallow or rocky areas, or for them to be triggered by large loads, such as a falling cornice or moving avalanche.

Moderate terrain choices with limited overhead hazard continue to be the best way to manage the uncertainty in the snowpack.

Watch for hazard ratings to rise Monday with a warm, wet Pacific flow incoming.

Confidence

Moderate

Avalanche Summary

Not much avalanche activity has been observed in this area during the past week, however in the thinner snowpack areas of the BYK region, we continue to see significant avalanches on the different persistent layers.

Snowpack Summary

A sun crust is present on steep solar slopes at treeline and below while 10-30 cm of soft snow can be found on northerly aspects. The various January persistent weak layer interfaces (sun crusts, facets, and surface hoar) are now down 60-120 cm. The weaker Nov. 16 basal facet layer is down 110-170 cm and continues to produce whumpfing and moderate to hard sudden collapse results in snowpack tests.

Weather Summary

Mainly cloudy skies with trace amounts of accumulation will persist overnight Saturday through Sunday with west-southwest winds peaking near 30km/h and alpine temperatures warming a bit to between -10 and -15C.

Sunday evening snowfall will increase to bring 5cm overnight as winds increase to 40km/h and shift southwest and a strong Pacific flow of moisture begins.

10-20cm of snow is expected Monday with freezing levels approaching 2000m and winds increasing to beyond 50km/h.

Terrain and Travel Advice

  • Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

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.

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.