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Avalanche Forecast

Archived

Apr 20th, 2021–Apr 21st, 2021

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

Regions

Kootenay Boundary.

 

Another hot day with a limited overnight freeze may initiate a spike in wet loose and possibly larger wet slab avalanche activity. Start and finish your day early and avoid sun-exposed terrain. Don't linger in runout zones and steer clear of cornices from above and below.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday: A mix of sun and cloud. Ridgetop wind generally light. Alpine temperatures near +7 C and freezing levels 2500 m.

Thursday: A mix of sun and cloud. Ridgetop wind light from the northwest. Alpine temperatures near +5 C. Freezing levels 2500 m.

Friday: Mostly cloudy with some sun. Ridgetop winds light from the South. Alpine temperatures +6 C and freezing levels 2400 m. 

Avalanche Summary

No new reports on Monday. 

Last 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 and cornices. 

  

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. With a limited freeze overnight on Tuesday, this crust may break down even faster (by noon) with mostly wet snow surfaces on Wednesday. Dry snow might still be found on northerly aspects in the high alpine. 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.
  • Keep in mind that wet avalanches can be destructive due to their high density.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • 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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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.