Avalanche Forecast

Archived

Apr 19th, 2021–Apr 20th, 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 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

South Coast.

Large and destructive wet slab avalanches have been active in adjacent forecast regions. Start and finish your day early to avoid exposure to sun-exposed avalanche terrain.

Steer clear of cornices overhead and plan your egress route carefully.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Tuesday: Sunny with light wind. Alpine high temperature near +10 and freezing level 2500 m.

Wednesday: Sunny with light wind. Alpine high temperature near +11 and freezing level 2900 m.

Thursday: A mix of sun and cloud and light wind. Alpine temperatures near +9 and freezing levels 2600 m.

Avalanche Summary

In the neighboring Sea to Sky region and the South Coast Inland, multiple wet slab avalanches were observed over the weekend near Whistler and on the Coquihalla, 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 will 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.

There have been a few reports of wet loose avalanches and cornice failures in recent days.

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 soft snow or isolated pockets of wind slab.

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.