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Avalanche Forecast

Archived

Apr 19th, 2021–Apr 20th, 2021

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

Regions

Kootenay Boundary.

Expect loose wet avalanche activity on sun-exposed slopes, especially in the afternoon. The best and safest riding may be found on high North facing terrain that is free of cornice hazard.

Check out the Forecasters' Blog on managing and understanding spring conditions. 

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Tuesday: Sunny. Ridgetop wind light from the South and alpine temperatures near +5. Freezing levels 2300 m by the afternoon and dipping down to 1300 m overnight.

Wednesday: Sunny. Ridgetop winds light from the northwest and alpine temperatures near +7. Freezing levels 2500 m. 

Thursday: Wet flurries (5-15 mm) at upper elevations, rain lower. Freezing levels 2400 m. 

Avalanche Summary

Over the weekend, reports of natural loose wet avalanches size 2-3 on solar aspects continued. Explosive work produced size 2-3.5 wet slab avalanches, failing on crusts in the upper snowpack and gouging to the ground as they ran to near valley bottom.

With all of this heat, sunshine, and little overnight crust recovery, I suspect this type of avalanche activity will continue through the forecast period. It's crucial to start early and end your day early as well as avoid solar slopes.  

Snowpack Summary

The snow surface consists of a melt-freeze crust on solar aspects and shaded aspects into the lower alpine, which transitions into moist/wet snow during the day. Dry snow might still be found on northerly aspects in the high alpine above 2200 m. There are no layers of concern in the snowpack, which has been melting and settling over the past week. Large cornices loom along many ridgelines. 

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Terrain and Travel

  • Avalanche hazard is expected to to increase througout the day, think carefully about your egress.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid lingering or regrouping in runout zones.

Problems

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.