Avalanche Forecast
Issued: Mar 20th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
ahanna,
Avalanche Canada
An easily triggered buried weak layer has surprised riders with large, deep avalanches recently. A tricky persistent slab problem is best managed through conservative terrain selection.
Summary
Confidence
Weather Forecast
Sunday night: Snowfall 3-10 cm. Moderate to strong southwest wind. Alpine low around -5 °C. Freezing level 800 m.
Monday: Snowfall 2-8 cm. Moderate to strong south wind. Alpine high around -1 °C. Freezing level rising to 1300 m through the day.
Tuesday: Snowfall 25-50 cm. Strong south wind. Alpine high around 0 °C. Freezing level 1500 m.
Wednesday: Snowfall 10-20 cm. Strong south wind. Alpine high around -6 °C. Freezing level 1000 m.
Avalanche Summary
Reports of persistent slab avalanches have been steadily coming in over the last few days from northwest of Terrace. These avalanche have been large to very large (size 2-3), failing on a weak layer buried 60-100 cm deep mostly on northeast facing slopes. These avalanches are easily triggered, some remotely and sympathetically, and and propagating long distances.
- On Saturday, a natural cornice-triggered storm slab stepped down to the persistent slab problem, simultaneously triggering a sympathetic persistent slab avalanche a short distance away.
- On Thursday and Friday, persistent slab avalanches were being triggered by riders and vehicles.
Other avalanche activity includes small natural and skier triggered wind slabs and loose dry avalanches up to size 1.5.
Snowpack Summary
40-80cm of recent snow has seen redistribution into wind slabs lee terrain features. Low elevations may hold 10-30 cm of wet/moist snow sitting over a widespread crust on all aspects below 1200 m.
50-100 cm below the snow surface, a weak layer of feathery surface hoar crystals could be preserved in sheltered terrain at and above treeline. This weak layer has started producing large avalanches, mostly north and west of Terrace, where moderate to heavy snowfall and wind have continued through the week. In areas further inland, where the storm tapered off earlier, this layer may not be at its tipping point, but I'd still be suspicious of it through the weekend.
A thick rain crust from mid-February is buried 100-150 cm. The snowpack below is well consolidated.
Terrain and Travel
- Uncertainty is best managed through conservative terrain choices at this time.
- Be alert to conditions that change with aspect and elevation.
- Caution around convexities or sharp changes in terrain.
- Be aware of the potential for remote triggering and large, deep avalanches due to the presence of buried surface hoar.
Problems
Persistent Slabs
A layer of surface hoar buried in early March is now 40-120 cm deep. It has surprised several skiers and machine operators recently with easy accidental and remote triggers producing large, widely propagating avalanches. Read more about how to manage this problem in our latest forecaster blog.
Aspects: North, North East, East.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Wind slabs remain triggerable in wind loaded terrain features such as ridge crests and roll-overs. If triggered, wind slab avalanches may step down to deeper layers resulting in larger avalanches.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 21st, 2022 4:00PM
