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Avalanche Forecast

Archived

Dec 18th, 2019–Dec 20th, 2019

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

North Rockies.

New snow and strong winds will result in CONSIDERABLE avalanche hazard, especially behind exposed ridges where wind slabs are likely to form. Increase the danger rating to HIGH for your area if 25 cm or more snow falls in a 24 hour period.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night: 5-10 cm new snow. Moderate southwest winds. Treeline temperatures around -4C.

Thursday: approximately 5 cm new snow during the day, with additional snow in the evening. Moderate southwest winds. Freezing level rising briefly to 1000 m in the afternoon.

Friday: 10-20 cm new snow. Strong southwest winds. Treeline temperatures around -4C.

Saturday: Flurries. Moderate southwest winds. Treeline temperatures around -8C.

Avalanche Summary

We have not had any reports of avalanche activity at the time of writing (Wednesday afternoon). Natural avalanches are most likely to occur below steep ridgelines in higher snow parts of the region.

Snowpack Summary

20-40 cm of recent storm snow lies on the surface. You can expect to find three weak layers buried between 30 and 60 cm below the surface. These surface hoar and facet/crust layers have shown signs of being reactive in snowpack tests and could become unstable with the weight of additional snow.

The lower snowpack contains several crust layers. In higher snow areas, these are likely well bonded. However, in shallow areas along the eastern slopes, these could be of concern.

Total snowpack depths are approximately 240 cm in the south of the region, 170 cm around Pine Pass and more like 120 cm in areas to the east.

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.