North Columbia

Surface instabilities and cornice hazards should be firmly on your radar as you travel. Expect stability to deteriorate over the course of each day.This is our final regular forecast of the season and will expire on April 25.

Moderate -

Tuesday: Mainly sunny. Light south winds, increasing to strong at ridgetop. Freezing level to 3000 metres with alpine high temperatures around +4. Weak overnight cooling.Wednesday: Sunny. Light west winds. Freezing level rising to 3500 metres by late afternoon and staying steady overnight. Alpine high temperatures around +6.Thursday: Sunny. Light south winds. Freezing level to 3300 metres with alpine high temperatures around +8.

Several smaller (size 1.5) natural wind slab avalanches were observed in the region on Saturday. These occurred primarily on northwest aspects above 2400 metres.Reports from Thursday were limited to a couple of size 2 storm and wind slabs, 30 and 50 cm deep, respectively. The storm slab released naturally while the wind slab was ski cut from a steeper north aspect in the alpine.Tuesday's reports included observations of numerous natural wind slab release from size 1-2 on north through east aspects in the alpine. A skier triggered size 2 storm slab resulted in a near miss. Another recent very large (size 3.5) storm slab was also observed to have released on a large, wind-loaded alpine feature. Observations from just over a week ago also showed a pattern of heightened cornice failure activity. Looking forward, a period of increasing warming, full sun, and warm overnight temperatures will be maintaining elevated chances of cornice and loose wet avalanche activity.

A surface crust is likely to exist on all but north aspects in the alpine and is expected to undergo melt-freeze cycles with daily warming and overnight cooling. Below the surface, about 50-70 cm of settled storm snow from the past couple of weeks overlies a supportive crust that exists on all but north aspects above about 2200 metres.This layer as well as the deeper (down about 90-120 cm) mid-March crust are of limited concern concern after warm temperatures have promoted settlement and bonding in the upper snowpack. Any remaining uncertainty with regard to their strength is generally limited to high north aspects as well as the possibility for triggering with a heavier load, such as a cornice collapse.Deeper persistent weak layers from December and January are generally considered dormant at this time but may be reactive to very large triggers. Cornice collapses become increasingly likely during periods of intense daytime warming.