Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 2020

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Rockies.

Heavy snow and warm temperatures are expected on Saturday which will result in dangerous avalanche conditions. Travel in avalanche terrain is not recommended.

Confidence

High - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather.

Weather Forecast

Friday night: around 10 cm new snow at high elevations, rain lower down. Strong southwest winds. Freezing level around 2000 m.

Saturday: around 20 cm snow expected with the potential for 30-40 cm in isolated areas in eastern areas. Expect rain at lower elevations. Strong to extreme southwest winds shifting to northeast in the afternoon. Freezing level around 1700 m.

Sunday: Dry and sunny. Light northwesterly winds. Freezing level around 500 m.

Monday: Dry with sunny breaks. Light notheasterly winds. Freezing level at surface with alpine temperatures around -10C.

Avalanche Summary

On Thursday a cornice fall released a size 2 slab avalanche on the slope below on an east aspect at 2150 m.

On January 16th, a natural, size 2 wind slab stepped down to the deep persistent basal facets below a rock band, details here.

Expect an increase in avalanche activity with the passage of the storm on Saturday, particularly in areas that see substantial amounts of new snow.

Snowpack Summary

New snow combined with strong southwesterly winds will continue to build slabs in exposed areas. Cornices have been noted in many areas. A crust can be found up to around 1700 m due to previous warming and sun exposure.

A well consolidated mid-pack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. While there has been little in the way of avalanche activity on this layer recently, the warm wet storm impacting this region has the potential to wake this layer up again. Areas that are most likely to harbor this problem are shallow, rocky start zones.

Terrain and Travel

Avoid all avalanche terrain during periods of heavy snowfall.

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.

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.