Avalanche Forecast
Issued: Feb 20th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
Conditions will deteriorate Sunday as a warm front brings new snowfall amid rising temperatures and cranking winds. Storm slabs are expected to become touchier at all elevations through the day. If you go into the backcountry, minimize your exposure to avalanche terrain.
Summary
Confidence
Weather Forecast
SATURDAY NIGHT: 5-15 cm of new snow, strong to extreme southwest wind, freezing level rising to 1000 m.
SUNDAY: 5-15 cm of new snow, strong to extreme southwest wind, freezing level 1500 m.
MONDAY: 5-20 cm of new snow overnight then clearing, freezing level dropping slightly to 1300 m, moderate to strong westerly ridgetop wind.
TUESDAY: Mix of sun and cloud, moderate westerly wind, freezing level 800 m.
Avalanche Summary
A size 1.5 loose dry avalanche was reported Friday out of steep rocky terrain near Valemount. As temperatures rise and winds ramp up Sunday, increased storm slab activity is expected at all elevations.
Snowpack Summary
Recent snowfall amounts have been highest in the south of the region near Blue River, and lowest in the north/east near Valemount. 10-25 cm of new snow is forecast to fall by the end of the day Sunday. This falls over 20-40 cm of recent low density snow which will likely experience rapid settlement Sunday as temperatures rise. At upper elevations, all of this recent snow will be easily blown around by strong to extreme westerly winds, forming thick, reactive slabs in lee features.
Below sits the old, extensively wind affected and faceted snow that sat on the surface during the extended cold, windy drought period. There is uncertainty around the strength of this interface with the new snow, which will surely be tested by the changes brought on by this active weather.
We've now got 40 to 80 cm of snow above the early February persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features like cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust.
Terrain and Travel
- Watch for changing conditions today, storm slabs may become increasingly reactive.
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
Problems
Storm Slabs
Between rising temperatures, ramping winds, and continued snowfall, 20-40 cm of recent low density snow is expected to develop into a slab overtop of weak, sugary facets on Sunday. Storm slab size and sensitivity to triggering will likely increase throughout the day.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A persistent weak layer buried 40 to 80 cm deep has produced recent large avalanches and is expected to become increasingly reactive this weekend. This layer has been most sensitive around treeline, but may also extend into alpine terrain and/or down into the trees.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 21st, 2021 4:00PM
