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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

South Coast.

Another hot day with no overnight freeze keeps the avalanche danger elevated. Wet slab avalanches are large enough to affect all elevations running full path to the valley. Don't linger in runout zones and steer clear of cornices from above and below. 

Confidence

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

Weather Forecast

Wednesday: Sunny with some clouds and light wind. Alpine temperatures near +10 C and freezing levels 3100 m.

Thursday: A mix of sun and cloud. Ridgetop wind light from the northwest. Alpine temperatures near +6 C. Freezing levels 2200 m.

Friday: Mostly cloudy with light precipitation. Ridgetop winds light from the South. Alpine temperatures +3 C and freezing levels 1700 m. 

Avalanche Summary

In the neighboring Sea to Sky region and the South Coast Inland, multiple wet slab avalanches were observed over the weekend and as of Monday, size 2-4. Many of these involved the full depth of the snowpack, running to the valley bottom. We suspect similar activity to have occurred in the South Coast region as well.

With all of this heat and sunshine with next to little overnight crust recovery, I suspect this type of avalanche activity could continue through the forecast period. It's crucial to start early and end your day early as well as avoid solar slopes. Wet slabs can be very large and destructive.

No new avalanche activity reported on Tuesday.

Snowpack Summary

High overnight freezing levels mean that the snow surface remains moist or wet. In places where the surface forms a crust overnight, it should quickly soften during the day with sunshine and warm temperatures. The highest elevation north aspects (above 2200 m) may still hold dry snow.

Cornices are large and looming along ridgelines. Sun and warm temperatures will increase the chances of cornice failures, especially when temperatures remain above zero overnight.

  

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.
  • Keep in mind that wet avalanches can be destructive due to their high density.
  • Avoid lingering or regrouping in runout zones.

Problems

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.