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Avalanche Forecast

Archived

Jan 6th, 2019–Jan 7th, 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 unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Weak layers buried near the bottom of the snowpack remain a concern. A conservative approach to route selection is recommended.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY NIGHT: Mostly cloudy, moderate west winds, alpine temperature -11 CMONDAY: Mix of sun and cloud, light to moderate west winds, alpine temperature -12 CTUESDAY: Cloudy with sunny breaks, light southwest winds, alpine temperature -7 CWEDNESDAY: Cloudy with sunny breaks, light southwest winds, alpine temperature -6 C

Avalanche Summary

A natural avalanche cycle may have occurred in the region with the substantial amount of recent snowfall on Thursday and Friday. Additionally there is a report of an explosives controlled deep persistent slab size 2.5 release on an east aspect at 2100m on Friday and also on Saturday of a size 2.5 explosives controlled wind slab release on a southeast aspect at 2000m.Last Wednesday, a naturally-triggered large (size 3) avalanche was observed near Elkford, which likely released on Tuesday. See here. It ran full-path to valley bottom. In the far west of the region, the snowpack has been observed to be weak and touchy, as described here.

Snowpack Summary

Large variability in snow depths still exists in the region, ranging from practically no snow to almost 200 cm. Upwards of 50-60 cm of snow fell late last week above 1500 m. The snow fell with strong southwest winds. Expect the deepest deposits in the lee of terrain features. This snow will sit on previous hard wind slabs, a scoured and shallow snowpack on exposed ridges, and soft snow in sheltered areas. Below 1500 m, expect to find wet snow that will freeze into a hard crust once temperatures cool.All of this recent snow has loaded a weak snowpack. For average snowpack areas, expect to find weak and sugary faceted grains around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks. It will take time for the snowpack to adjust to the added load.

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.

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.