Avalanche Forecast

Issued: Jan 18th, 2021 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs, Loose Wet and Persistent Slabs.

Avalanche Canada dsaly, Avalanche Canada

Another heavy punch of moisture and wind. Avoid all avalanche terrain during periods of rapid loading from snow and wind.

Summary

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

MONDAY NIGHT - Cloudy with flurries, snowfall increasing later in the day / increasing southwest wind, gusting upwards of 100 km/h / alpine low temperature near -1 / freezing level spiking overnight with extreme winds

TUESDAY - Snow starting late Monday, 25-35 cm / Strong southwest wind, gusting upwards of 80 km/h / alpine high temperature near -2 / freezing level 1000 m dropping to valley bottom

WEDNESDAY - Cloudy with isolated flurries / northwest wind, 20-30 km/h / alpine high temperature near -4 / freezing level valley bottom

THURSDAY - Cloudy with sunny breaks / northeast wind, 10-20 km/h / alpine high temperature near -8 / freezing level valley bottom

Avalanche Summary

Another natural avalanche cycle occurred Saturday night into Sunday morning: Storm slab avalanches to size 2.5 at treeline and above; large (size 2-3) wind slab avalanches failing in steep, lee alpine features; and small (size 1) wet-loose avalanches below treeline

A natural avalanche cycle occurred Thursday into Friday, large (size 2-3) storm slab avalanches were reported along highway corridors. The largest (size 3) avalanches were observed in wind-loaded start zones in the alpine and treeline, but also included below tree line avalanches to size 2 failing on unsupported features. Wet-loose avalanches to size 1.5 were reported from steep rocky slabs below tree line.

There were a few natural avalanches up to size 3 reported in the north of the region on Wednesday. There was also one remotely triggered size 3 persistent slab avalanche reported in the north of the region.

There was a natural avalanche cycle reported on Tuesday, additionally explosives triggered numerous avalanches up to size 2.5 and people triggered a few size 1 avalanches.

Last Monday, there were reports of widespread natural and explosives triggered avalanches up to size 3. The largest avalanches were reported in the north of the region where there has been more recent snow. The avalanches being reported closer to Terrace were generally in the size 1-2 range.

Snowpack Summary

Storm snow in the last week totals upwards from 60-100+ cm, with 20-50 cm fresh, lower-density snow over older, more settled snow. Southerly winds reached into mature trees and mild temperatures have encouraged settlement. Below 800 m rain on snow produced a moist snowpack, a wet-loose problem will persist where the snowpack is moist or wet.

For the most part, the snowpack is well settled and deeper instabilities in the snow pack are of little concern. We're tracking a few uncertainties, in the Shames area, a weak layer of surface hoar has been reported in sheltered areas down around 120-180 cm. And a bit further north in the Nass/Sterling/Beaupre areas, there is potentially still concern about an older weak layer of surface hoar overlying a crust that is now roughly 180-200 cm deep. And in the far north of the region, there is concern about weak snow at the bottom of the snowpack.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs

Heavy snowfall will rapidly load the snowpack. Expect slabs to be widespread and reactive.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 2.5

Loose Wet

An icon showing Loose Wet

Freezing levels are expected to spike overnight and drop through Tuesday. Avoid steep slopes and terrain traps at low elevations where snow is wet.

Aspects: All aspects.

Elevations: Below Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

We've been tracking a few different persistent weak layers in the snowpack. They are all generally buried between 100-200 cm and tend to consist of either surface hoar or crusts with faceted snow sitting on them. Recent storms and snow added a huge load and tested these layers deeper in the snowpack. Moving forward the mid-pack is generally well settled and these layers are becoming quite stubborn to human trigger and likely trending to dormancy, however still pose the "low probability, high consequence" scenario.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 3

Valid until: Jan 19th, 2021 4:00PM