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Avalanche Forecast

Archived

Dec 15th, 2023–Dec 16th, 2023

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

Regions

Glacier.

Triggering the Dec 1st surface hoar is still possible in areas that have not avalanched and the safest way to manage this problem, is through conservative terrain choices.

Confidence

Moderate

Avalanche Summary

Thurs overnight the wind triggered two sz 2.5 natural avalanches off the north face of Mt. Macdonald.

On Thurs near the park boundary, an experienced group triggered a size 2 avalanche on the Dec 1 surface hoar and 1 skier was partially buried.

On Tuesday, a group triggered a size 2.5 on Ursus Minor. This avalanche was triggered in a wind loaded pocket near ridge top, in a shallow & faceted snowpack. Wide, impressive propagation occurred on the Dec 1 surface hoar, facet layer.

Snowpack Summary

16cm of storm snow buries a new surface hoar layer, which sits on top a thin sun crust in steep terrain.

A rain crust down 40cm is present up to 2100m.

A weak layer (Dec 1 surface hoar) buried 80-110cm deep continues to produce 'sudden' results in snowpack tests and human triggered avalanches. The surface hoar sits on a sun crust on solar aspects at upper elevations.

The base of the snowpack is facetted at upper elevations.

Weather Summary

A weak system brings light precipitation while over the next few days a ridge of high pressure moves into the interior.

Tonight: trace precip, -6°, Strong SW winds

SAT: 5cm, -5°, Moderate SW Winds, Fz lvl 1300m

SUN: trace precip, -5°, Light SW Wind, Fz lvl 1300m

MON: Mostly cloudy, trace precip, High -1°, Fz lvl 1800m

Terrain and Travel Advice

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.