Avalanche Forecast

Issued: Mar 27th, 2021 4:00PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs.

Avalanche Canada kdevine, Avalanche Canada

Email

Although the storm is expected to ease off on Sunday, avalanche danger remains elevated and human triggered avalanches are likely. Choose conservative terrain with no overhead hazard.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SATURDAY NIGHT - Snow, 10-20 cm / strong west wind / alpine low temperature near -8 / freezing level at valley bottom

SUNDAY - Flurries in the morning, easing off mid-day / moderate northwest wind / alpine high temperature near -6 / freezing level 800 m 

MONDAY - Cloudy with scattered flurries / moderate northwest wind / alpine high temperature near -6 / freezing level 800 m 

TUESDAY - Cloudy with flurries / strong west wind / alpine high temperature near -4 / freezing level 1200 m

Avalanche Summary

Natural avalanche activity is expected to continue into Sunday morning, likely tapering throughout the day. Keep in mind that the likelihood of human triggered avalanches will remain high.

A widespread avalanche cycle likely occurred during the day on Saturday.

On Thursday, Explosive control work conducted east of Kitimat resulted in cornices failures up to size 2.5, and wind slabs limited to size 1. Dry loose avalanches were also observed up to size 1.5. Around Ningunsaw, there were explosive-triggered avalanches up to size 3, including one that is suspected to have failed on the mid-February persistent weak layer.

Tuesday's storm resulted in a widespread natural avalanche cycle, with size 2-3 storm slab avalanches at upper elevations, and size 1-1.5 wet loose avalanches below treeline.

Several size 2-3 natural glide slab avalanches have been reported over the last week. Avoid slopes with glide cracks on them at all times. They are inherently unstable and can release at any time.

Snowpack Summary

10-20 cm is expected on Saturday night, adding to the 30-40 cm that fell during the day on Saturday. Storm slabs are expected to be widespread and reactive at upper elevations. Below treeline saw heavy rainfall on Saturday, but may get some snow on Saturday night as freezing levels drop.

A crust is now buried 80-120 cm below the surface on solar aspects and below 1400 m. At higher elevations where this crust tapers out, the new snow has added significant load to a couple of deeply buried weak layers that we haven't quite ruled out as problems.

The first and most concerning persistent weak layer was buried in mid-March and is around 120-180 cm deep. It consists of surface hoar on sheltered northerly aspects around treeline. 

Down between 170 to 300 cm is another layer of surface hoar and facets, buried in mid-February. This layer may still be a concern in shallower snowpack areas. 

There is a chance that further loading during the storm could result in some large persistent slab avalanches.

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Make conservative terrain choices and avoid overhead hazard.

Problems

Storm Slabs

An icon showing Storm Slabs

Natural avalanche activity is expected to taper throughout the day as the storm eases off, but human triggered avalanches will remain likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1.5 - 2.5

Valid until: Mar 28th, 2021 4:00PM