Previous large avalanche on early December layer

Simpson Bowl Banff Yoho & Kootenay National Park

Ken B√ČLANGER_Elevation Guides , Friday 14th January, 2022 10:10PM

We were up in Simpson Bowl today for the first day of an AST2 course. Due to last season's closure for a denning grizzly, it had been two years since I was last up there. I noticed a significant difference as soon as we crested the creek into the hanging valley: where there used to be a 20-30 year old gladed forest of sub-alpine fir, it was now open all the way to the bowl.

We dug some snowpits at 2175 metres to investigate the early December layer down ~90 cm, and found significant avalanche debris in the crust/facet combo layer: now I know where those trees went...

Not much reactivity on this layer with multiple compression tests. At this elevation most of the precip in early Dec likely fell as snow or sleet, and a sz 3 to 4 avalanche had cleaned it up.

We directly observed three sz 1 windslabs high above on E and SE aspects in the alpine at ~2500 metres that stopped mid track. Temps were inverted, we recorded -2.5C at the pit so extrapolated it may have been close to 0C in the ALP.

Source: Mountain Conditions