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Avalanche Forecast

Archived

Apr 6th, 2022–Apr 7th, 2022

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

Recent storm snow combined with significant warming is driving the avalanche hazard to HIGH, especially by the afternoon. 

Check out the Forecaster Blog for additional details.

Confidence

Moderate -

Weather Forecast

Thursday: Cloudy with some sunny periods in the morning. WARM. Freezing levels rise to 2500 m by the afternoon. Alpine temperatures +3C and ridgetop wind moderate to strong from the southwest. 

Friday: No overnight refreeze and WARM. Cloudy with snow above 1500 m 10-15 cm. Freezing levels stationary at 2500 m with alpine temperatures near +3C. The freezing level should start to fall overnight and into Saturday.

Saturday: Cloudy with new snow up to 10 cm. Freezing levels drop to the valley bottom and ridgetop winds switch to the northwest. 

Avalanche Summary

No recent reports since last weekend. 

Warm temperatures and will likely trigger a natural avalanche cycle on Thursday and Friday

On Sunday, a small natural wind slab avalanche was observed on a north aspect in the alpine. A rider triggered a small slab avalanche on the same slope. Both avalanches likely occurred on Saturday.

On Saturday, many natural dry loose avalanches were reported in steep terrain, as well as a large cornice failure that released a slab on the slope below. 

Snowpack Summary

Thursday's warming will likely create moist/ wet surface snow on all aspects and elevations besides high true North.

25 to 50 cm of new storm snow blankets upper elevations with the greater snowfall amounts being in the Renshaw. Strong west to southwest wind will be redistributing the new storm snow in exposed high elevation terrain forming touchy wind slabs and developing large cornices. The upper 60 cm of the snowpack consists of multiple crusts. 

30-70 cm of snow sits on the thick melt-freeze crust from late March. 

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Cornices become weak with daytime heating or solar exposure.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.