Avalanche Forecast
Issued: Mar 11th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
wlewis,
Avalanche Canada
Keep terrain selection conservative while storm snow gains strength.
Slabs will be more reactive where they sit over a crust on south facing slopes and in sheltered terrain where buried surface hoar lingers.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Snowfall tapers off Saturday afternoon. Sunday brings a brief break in the snow and wind with another active front forecast to hit late evening.
FRIDAY NIGHT: Cloudy, 10-15 cm of snowfall possible. Southwest winds ease to strong, alpine high -2 °C, freezing levels around 500 m.Â
SATURDAY: Mainly cloudy, flurries continue with 5 cm possible, moderate southwest winds. Alpine high -3 °C, freezing levels rise to 1000 m.Â
SUNDAY: A mix of sun and cloud. Isolated flurries possible. Light to moderate southwest winds. Freezing level around 1000m. Alpine high -3.Â
MONDAY: Light snowfall begins overnight, around 15 cm by morning and another 15 cm possible over the day. Freezing levels around 1000 m. Alpine high -3. Strong southwest winds.Â
Avalanche Summary
Friday morning, large explosive charges were able to trigger multiple size 1.5 storm slabs, up to 20cm deep. We expect storm slabs to be reactive to human triggers, with natural activity possible where accumulations are greatest.Â
Over the last 10 days, a few size 1-2 persistent slabs have been triggered on the buried weak layers described in the snowpack summary section. Avalanches were mainly triggered on North through East aspects, between 1200 and 1800 m. Recent activity suggests they are becoming less reactive with the last reported avalanche on Sunday the 6th.
Snowpack Summary
Storm snow accumulates over a crust on sun affected slopes and on hard wind hammered surfaces in most terrain features. A layer of surface hoar may sit below the storm snow in isolated terrain features.
Low elevations may see a mix of snowfall and rain falling on a widespread crust on all aspects below 1000 m.
Several weak layers sit in the upper/mid snowpack that have been recently reactive. A layer of surface hoar buried early March is down 15-30 cm, preserved in wind sheltered terrain features at treeline. Another layer of weak surface hoar from late February is buried 35-60 cm deep, and is most prominently at treeline elevations. A thick crust from mid-February is buried 70-110 cm. The snowpack below is well consolidated.
Terrain and Travel
- As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be careful as you transition into wind affected terrain.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Storm Slabs
Storm slabs will continue to build overnight and into Saturday morning. Expect strong west/southwest winds to build larger slabs in east facing terrain features. Slabs will be most reactive where it overlies a smooth crust, and/or surface hoar.
At lower elevations, precipitation may be mixed or fall as rain. Expect wet avalanches to be likely where heavy, wet snow exists - and where rain breaks down the crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
New load will increase the likelihood of triggering avalanches on deeper layers, creating large avalanches. Storm slabs in motion or cornice falls may affect these persistent weak layers. Use extra caution during heavy snow, rain or wind.
- Two spotty layers of weak surface hoar are buried in the top 60cm of the snowpack, mostly found in treeline and low alpine features sheltered from the wind and sun.
- A widespread, thick crust is buried 60-100 cm deep.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 12th, 2022 4:00PM
