Avalanche Forecast
Issued: Feb 4th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Avalanche hazard will increase throughout the day. Simplify terrain choices where more than 25 cm of new snow accumulates and seek out sheltered areas with soft loose snow.
Summary
Confidence
Weather Forecast
Tuesday night: Cloudy, 5-10 cm of snow, strong southwest winds, alpine temperature -11 C.
Wednesday: Cloudy, 10-20 cm of snow, moderate southwest winds with strong gusts, alpine high temperature -5 C, freezing level rising to 800 m.
Thursday: Partly cloudy, isolated flurries, light west winds, alpine high temperature -4 C.
Friday: Mix of sun and cloud, light southwest winds, alpine high temperature -6 C.
Avalanche Summary
New snow, wind, and gradually warming temperatures are expected to build a reactive storm slab problem prone to human-triggering where more than 25 cm accumulates. These conditions may also bring cornices to their breaking point.
During the weekend storm, numerous small to very large (size 1.5-4) avalanches released naturally in the storm snow. These avalanches primarily occurred on leeward aspects at treeline and alpine elevations. Below tree line, wet loose avalanches were releasing naturally during the warm temperatures on Friday.
With continuous stormy weather over the past week, operators have reported three persistent slab avalanches that were both naturally and skier-remote triggered. These very large (size 2.5-4) avalanches were breaking 100-200 cm deep across a variety of aspects above 1900 m. Storm slab avalanches or cornice fall may have the potential to step-down to this layer.
Snowpack Summary
The forecast storm is expected to bring 30+ cm to favored areas west of Valemount. Strong west winds are forecast as well as a gradual warming trend throughout the storm, which has the potential to speed up slab formation.
There have been substantial changes to the snowpack over the past few days. 40-60 cm of snow fell during the weekend storm above 1700 m. Higher snow totals fell in the southeastern parts of the region. Strong winds originating from the southwest and shifting to the northwest have created a tricky loading pattern near and above tree line and have elevated concern for cornice triggers. Check out this MIN and this MIN for a helpful illustration of these conditions. During a warming event Saturday night, rain saturated snow surfaces up to around 1700 m that have since formed a crust.
The mid and lower snowpack are generally well settled and strong, however there is a weak layer of surface hoar currently buried 70 to 150 cm deep. This layer has shown signs of instability in the region on slopes between 1700-2400 m, and it may require more time to heal.
Terrain and Travel
- Watch for changing conditions today, storm slabs may become increasingly reactive.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
- If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
Problems
Storm Slabs
20-30 cm of snow is forecast to accumulate by Wednesday afternoon. Strong west winds and temperatures rising during the storm will speed up slab formation as new snow accumulates. Expect storm slabs to become increasingly reactive throughout the day. New snow and wind may bring cornices to their tipping point.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of buried surface hoar may persist deeper in the snowpack in the southwest of the region. Easier-to-trigger storm slab avalanches or cornice falls could potentially step down to this persistent slab problem resulting in a very large avalanches.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Feb 5th, 2020 5:00PM
