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 Inland.

Wet slab and wet loose avalanches have been reactive with the recent warm weather. 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 - Confidence is due to a stable weather pattern with little change expected. Uncertainty is due to the limited number of field observations.

Weather Forecast

Tuesday: Sunny with light wind. Alpine high temperature near +4 and freezing level 2500 m.

Wednesday: A mix of sun and cloud with light to moderate wind. Alpine high temperature near +6 and freezing level 2600 m.

Thursday: A mix of sun and cloud and light wind. Alpine temperatures near +4 and freezing levels 2200 m.

Expect the Alpine temperatures in the South on the Coquihalla to be warmer (+10-12 degrees) by the afternoon) than North on the Duffy.

Avalanche Summary

The few reports still trickling in confirm that widespread loose wet and cornice activity was still ongoing as of the weekend. The Coquihalla zone has also seen glide slabs up to size 3 and 2 wet slab avalanches up to size 2 on Sunday.

In the neighboring Sea to Sky region, multiple wet slab avalanches were observed over the weekend near Whistler, 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 Inland region as well.

Snowpack Summary

A slight dip in overnight freezing levels combined with radiant cooling has formed a melt-freeze crust from 1700-2200 m. At lower elevations the snowpack is isothermal. The crust will likely break down quickly with solar radiation and freezing levels through the roof. Steep north aspects above 2200 m and higher may still hold dry wintery 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.