Avalanche Forecast

Issued: Apr 21st, 2021 2:00AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Cornices and Wet Slabs.

Ryan Shelly, VIAC

Vancouver Island.

Cornice fall and wet loose avalanches on steep/rocky and unsupported terrain observed at Alpine elevation band.

Summary

Past Weather

Warm double digit air temperatures continue to melt surface snow, destabilize upper snowpack layers and weaken cornices.

Weather Forecast

Freezing levels will continue to drop over the next several days. Below freezing air temperatures expected by Friday at Mid mountain elevation band across Vancouver Island. Wednesday: No new precipitation, Winds light from the NW (moderate NW gusts in afternoon for North and Central Island), Freezing level 2,300 meters Temps at 1500 meters up to +8 degrees.Thursday: No new precipitation, Winds light from the North, Freezing level 1,750 meters. Temps at 1500 meters up to + 3 degrees.Friday: Less than 5cm Snow/5mm Rain (depending on elevation) expected in late afternoon, Winds light from the South, Freezing level 1,400 meters. Temps at 1500 meters -1 degrees.

Terrain Advice

Please respect the current closures at Mount Washington, no access is permitted at anytime on the ski areas slopes or terrain.During periods of intense warming and sunshine, avoid solar facing terrain.Avoid travelling both above and below cornices.Early starts may help to ensure you can accomplish your trip objective prior to arrival of day time highâ€™s when the snowpack will become increasingly more unstable.Major concern remains with the fact that no below freezing temperatures are taking place on Vancouver Islandâ€™s mountain ranges overnight. Expect continued destabilization within the layers that exist within the upper snowpack. On Friday air temps will cool and help consolidate melting snow problems. Possibility of isothermal snow may make for extremely challenging and dangerous travel as snow may readily collapse under an individualâ€™s weight.

Snowpack Summary

Melting (isothermal snow) exists within the upper 10cm of the snowpack. A series of layers exists within the upper snowpack that are weakened as a result of the consistent above zero air temperatures. Snow is retaining below zero degree composition down 50cm from the surface of the snowpack where an intact ice layer remains frozen and reactive (stubborn/hard range) to testing.

Snowpack Details

Surface: 5-10cm of isothermal melting snow.
Upper: Down 30cm from the surface, a wet (water/snow) interface, upper snowpack is dense and supportive.
Mid: Well settled and dense. Contains a series of ice layers (still fully frozen/below zero degrees) reactive to testing
Lower: well settled and dense

Confidence

Moderate - On Friday, below zero degrees air temperatures will return to Vancouver Island mountain ranges. Solar Aspects remain primary concern with day time heating. Avalanche ratings reflect the highest danger level expected over the course of the day.

Problems

Cornices

Expect Cornices to remain unstable and although it is possible many weak cornices have already collapsed this past week, there exists many fully intact cornices at tree-line and alpine elevation bands. Location: Predominantly north aspects at ridge top in the Alpine and Tree line. Possibility: Triggering of this avalanche problem is likely to possible from light loads such as skiers. Natural avalanches are possible to unlikely later in the week. Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3

Likelihood

Possible

Expected Size

1 - 1

Wet Slabs

Melt water has percolated into upper snowpack layers. Formal snowpack assessments have revealed melt water destabilizing specific upper snowpack interfaces/layers. It is possible that despite cooling trend surface snowpack may consolidate faster than these melt water interfaces found down 35cm to 50cm of the upper snowpack. Please be cautious and assess stability prior to stepping out into steep unsupported slopes as wet slabs could become an issue over the next several days. Location: All aspects and all elevation bands. Possibility: Triggering of this avalanche problem is possible from light loads such as skiers and snowmobilers. Natural avalanches are unlikely. Size: If triggered expect these avalanches to be small size 1 in specific areas and on isolated terrain features large, size 2

Likelihood

Possible

Expected Size

1 - 1

Valid until: Apr 22nd, 2021 2:00AM