North Rockies Avalanche Forecast

Issued: Apr 19th, 2021 4:00PM

Tue Apr 20th Current Conditions
Alpine Considerable Treeline Considerable Below Treeline Considerable
Wed Apr 21st 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Moderate
Thu Apr 22nd 3 Day Outlook
Alpine Low Treeline Low Below Treeline Low

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

Wet loose avalanches become increasingly likely during the heat of the day. Back off slopes as the surface becomes moist or wet with daytime warming and avoid slopes with large cornices overhead. 

Summary

Confidence

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

Weather Forecast

  

MONDAY NIGHT: Clear / Light, north ridgetop wind / alpine low temperature -6 / Freezing level 1000 m.

TUESDAY: Sunny / Light, northwest ridgetop wind / alpine high temperature 8 / Freezing level 2400 m.

WEDNESDAY: Mostly sunny / Moderate, northwest ridgetop wind / alpine high temperature 6 / Freezing level 2000 m.

THURSDAY: Mostly sunny / Light, north ridgetop wind / alpine high temperature -2 / Freezing level 1100 m.

Avalanche Summary

A size 3 naturally triggered wet slab avalanche was reported on a southwest aspect in the alpine near McBride on Monday.

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

Successive days of very high freezing levels created moist surfaces at all elevations/aspects. Clear skies and cooling temperatures have formed firm crusts overnight which will lock up the snowpack until the surface crust melts. Avalanche danger can increase rapidly after the sun melts the frozen snow surface and begins to penetrate deeper into the snowpack. Strong solar radiation and warming often trigger wet loose avalanches and large cornice failures. Cornice falls could trigger large avalanches on deeply buried weak layers. 

Strong solar radiation and warm temperatures have the potential to reactivate deeply buried weak layers such as 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 and should be avoided.

Terrain and Travel

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

Problems

Cornices

An icon showing Cornices

Likelihood

Possible

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

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.

Wet Slabs

An icon showing Wet Slabs

Likelihood

Unlikely-Possible

Expected Size

2.5 - 3.5

A prolonged period of warm air and sunny skies have dramatically warmed the snowpack, increasing the likelihood of reactivating deeply buried weak layers. It is uncertain if and when large slab avalanches may release, but the possibility remains during periods of strong solar radiation. In general, steep, rocky slopes with a shallow or thin to thick snowpack are most suspect and should be avoided.

Aspects:

East, South East, South, South West, West.

Elevations:

Alpine.

Valid until: Apr 21st, 2021 4:00PM

Forecast Trend

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