Avalanche forecast

North Rockies

Feb 25 – 27, 2021Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Conservative terrain selection is CRUCIAL right now. Large human triggered avalanches remain possible as the next wave of storms impacts the region. There was a recent fatal avalanche in the region and the upper snowpack continues to be overwhelmed by significant snow & wind. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3

    Ongoing heavy snowfall and an overall warming trend has setup a scenario where it's possible for humans to trigger deep slabs. These slabs are failing on a layer of surface hoar that developed in late January. The layer can be found 50 to 110 cm deep across the region, being deepest in the south and shallowest in the north. This layer has been the most sensitive right at treeline, but it may extend up into the alpine, and be found in openings in the trees below treeline. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–2

    The next wave of storms is expected to deliver significant amounts of new snow and wind over the next few days which will likely form yet another round of fresh sensitive storm slabs. All the while, the snowpack is still adjusting to the 30 to 70 cm of warm snow that fell last weekend. The upper snowpack needs time to adjust to this new load and really can't be trusted right now.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

The region continues to be in the storm track through the weekend.

WEDNESDAY NIGHT: Freezing level at valley bottom, strong southeast wind, 5 to 12 cm of snow expected.

THURSDAY: Overcast, freezing level rising to about 1000 m, strong west/northwest wind, 6 to 12 cm of snow expected during the day with 5 to 15 cm Thursday night.

FRIDAY: Broken cloud cover, freezing level at valley bottom, moderate to strong northwest wind, no snow expected during the day, 2 to 5 cm possible Friday night.

SATURDAY: Overcast, daytime temperature at valley bottom beginning around -15 rising to near 0 C during the day, strong southwest wind, 4 to 8 cm of snow expected during the day with 10 to 20 cm Saturday night.

Avalanche Summary

Widespread whumphing was reported Tuesday which is a clear sign of an unstable snowpack. More details in this MIN report.

There was likely a widespread natural avalanche cycle on Sunday and Monday as a result of heavy loading from snow and wind.

There were numerous reports of touchy conditions on Sunday as evidenced here and here. 

There was a fatal avalanche accident in the Hasler area on Saturday. The incident occurred on a northeast aspect between 1400 and 1600 m. The avalanche was a size 2.5. The fracture line was estimated to be 50-100 cm and is suspected to have been a persistent slab avalanche running on a weak layer of surface hoar. Click here to link to a report on the incident.

Snowpack Summary

The north of the region has seen little snow since Monday night, but the south of the region picked up an additional 10 to 25 cm of snow. This adds to the 40-60+cm of warm snow that fell through the weekend with strong southwest and west winds which formed reactive storm slabs and wind slabs in exposed terrain.

All the new snow in the last week has increased the load on a widespread persistent weak layer consisting of surface hoar. The layer is likely 80-120 cm deep near Renshaw and 60-100 cm deep around Torpy and further north. Reports suggest this layer is most prevalent around treeline elevations, but likely reaches into the alpine and down into the trees too. It may sit above a crust below 1600 m. The likelihood of triggering this layer has likely increased with the new load from the snowfall. The consequence of triggering this layer is high.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • In times of uncertainty conservative terrain choices are our best defense.

Regions covered