North Rockies Avalanche Forecast

Issued: Apr 17th, 2021 4:00PM

Sun Apr 18th Current Conditions
Alpine Considerable Treeline Moderate Below Treeline Moderate
Mon Apr 19th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Moderate
Tue Apr 20th 3 Day Outlook
Alpine Considerable Treeline Considerable Below Treeline Considerable

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Cornices, Loose Wet and Deep Persistent Slabs.

Cloudy skies may prevent the snow surface from freezing overnight. Expect the danger to be CONSIDERABLE in areas where the snow surface doesn't freeze into a strong crust overnight.

Check out the latest Forecaster's Blog for more information on managing current conditions.

Summary

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

  

SATURDAY NIGHT: Cloudy with isolated flurries; 3-10 cm. / Strong, northeast ridgetop wind / alpine low temperature -2 / Freezing level dropping to 1500 m.

SUNDAY: Mix of sun and cloud / Strong, northeast ridgetop wind / alpine high temperature 1 / Freezing level 1500 m.

MONDAY: Sunny / Light, northeast ridgetop wind / alpine high temperature 3 / Freezing level 1800 m.

TUESDAY: Sunny / Light, northwest ridgetop wind / alpine high temperature 7 / Freezing level 2300 m.

Avalanche Summary

Numerous explosive triggered wet slab avalanches size 3-3.5 and one size 3.5 deep persistent slab avalanche were reported on solar aspects on Friday.

There have been some large deep persistent slab avalanches triggered by warming to the south around Jasper and Banff, and we suspect this problem may extend into the North Rockies.

Sustained warming can increase the likelihood of large avalanches failing on deeply buried weak layers.This is most likely to occur on steep, rocky alpine slopes with a shallow or thin to thick snowpack. 

Snowpack Summary

Forecast flurries and strong northeasterly winds Saturday night may form small wind slabs on lee features below ridgetops.

Warm temperatures are melting the surface on all but the highest north-facing slopes, creating weak surface snow during the heat of the day. Crusts may form overnight. 

 Strong solar radiation and warming will likely trigger the large cornices that hang over ridgelines. Cornice falls could trigger large avalanches on deeply buried weak layers. 

As heat penetrates deeper into the snowpack it has the potential to reactivate deeper weak layers, including a layer from mid-February and weak facets at the bottom of the snowpack. The most likely areas to be concerned about deeper weak layers are shallow parts of the region along the eastern slopes of the Rockies like Core Lodge, Wolverine, Bullmoose, Upper Burnt and perhaps around Mt. Robson. In general, steep, rocky slopes with a shallow or thin to thick snowpack are most suspect.

Terrain and Travel

  • Avoid travelling on slopes below cornices.
  • Avoid exposure to sunny slopes, especially in the afternoon.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

Problems

Cornices

An icon showing Cornices

Likelihood

Possible-Likely

Expected Size

2 - 3

Cornices are large and will weaken with daytime warming. Stay well back from them on ridges and avoid travelling beneath them. A cornice fall has the potential of triggering slabs on the slopes below.

Aspects:

North, North East, East, North West.

Elevations:

Alpine.

Loose Wet

An icon showing Loose Wet

Likelihood

Likely

Expected Size

1 - 2.5

Expect natural wet loose avalanches to occur when the sun comes out. The most likely areas to get into trouble are above terrain traps.

Aspects:

All aspects.

Elevations:

All elevations.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Possible

Expected Size

2.5 - 3.5

A prolonged period of warm air and sunny skies is heating the snowpack, increasing the likelihood of reactivating buried weak layers. It is uncertain if and when large slab avalanches may release, but the possibility remains during this warm period. Deeper releases are most likely in shallow snowpack areas along the eastern slopes of the Rockies.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

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

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.