The beginning of the week saw weak to non-existant overnight freezes and an isothermal snowpack extending from roadside elevations (~1300m) up to treeline. During the days, weak surface crusts formed overnight would breakdown quickly and avalanche hazard increased rapidly with daytime heating and solar input. Weak and newly enlarged cornices (from a major storm event the previous week) were our major concern-- from exposure to the cornices themselves and as triggers for slopes below.
Wednesday, April 22nd saw a major rainfall event with rain extending to 1800/2000m in most locations. This saturated the upper 50cm of the snowpack and produced many loose snow avalanches on all aspects from below treeline to ridgetop. A major natural avalanche on Chipmunk Mtn, (sz 4 with a 1-2m deep crownline extending 550m across) occurred during this period.
Thursday and Friday (22nd and 23rd) saw stronger overnight freezes and generally cooler temperatures during the days. This resulted in the development of a 5-10cm thick crust layer at the snow surface which helped stabilize the snowpack. However, weak and saturated snow still exists below this crust and when temperatures rise and solar input increases, expect this surface crust to weaken and stability to decrease rapidly.
Cornices remain a major concern, especially when exposed to sun and rising daytime temperature. The major avalanche that occurred during the rain event also indicates that deep instabilities in the snowpack can "wake up" during periods of higher freezing levels and increased precipitation (rain).
Excellent spring skiing was found, specially after daytime warming softened the surface layers but hard boiler plate skiing was also experienced on North aspects above 2000m. The Singing Pass trail ski out was still passable as of Friday April 23 but is deteriorating quickly at lower elevations.
Thanks to all the candidates for their input.
Sylvain Hebert
ACMG Ski Guide