Observations from an AST1 in the Grizzly Den area 091219-20. This place is technically located at the north edge of the North Columbia bulletin region but is historically similar to the conditions across the Rocky mountain Trench in the McGregor Range of the Rocky Mountains. At valley bottom, (1100m) the HS is about 100cm. A thin rain crust from 091218 extends up to near the top of the cut block, (1350m). The HS at the top of the block was about 130-150. Above there the snow is well settled from the warm weather on the 18th. Ski penetration was about 15cms. At treeline, (1800m) on Leprechaun Ridge the HS varied between 160 and 200 cm. A bunch of stability tests on the east aspect of the ridge showed consistent hard results down about 140 cm in large facets in a crust complex within 40 cm of the ground. The snow pack up there can be described as windslab on the surface varying in depth and resistance. Under the slabs is a layer of small facets extending up to 40 cm down into the pack. The mid pack is generally well settled and strong. The aforementioned crust/facet complex near the ground appears to be the only other significant layer. Of note was the observation of the crown of a fairly large avalanche the ran down the west face of Leprechaun Ridge. The crown wasn’t there when one of the group was there on 091217. However strong east wind were moving lots of the low density surface snow at that time and we hypothesized that loading associated with those winds onto shallow facetted snow near the ridge crest combined with the rapid warming on the 18th likely resulted in the avalanche. Visibility was limited but no other avalanche activity was observed. Skiing quality was good down to the cut block where the crust made turns a bit of a challenge. Snowing and blowing hard from the east when we left.
Observations from an AST1 in the Grizzly Den area 091219-20. This place is technically located at the north edge of the North Columbia bulletin region but is historically similar to the conditions across the Rocky mountain Trench in the McGregor Range of the Rocky Mountains.
At valley bottom, (1100m) the HS is about 100cm. A thin rain crust from 091218 extends up to near the top of the cut block, (1350m). The HS at the top of the block was about 130-150. Above there the snow is well settled from the warm weather on the 18th. Ski penetration was about 15cms. At treeline, (1800m) on Leprechaun Ridge the HS varied between 160 and 200 cm. A bunch of stability tests on the east aspect of the ridge showed consistent hard results down about 140 cm in large facets in a crust complex within 40 cm of the ground. The snow pack up there can be described as windslab on the surface varying in depth and resistance. Under the slabs is a layer of small facets extending up to 40 cm down into the pack. The mid pack is generally well settled and strong. The aforementioned crust/facet complex near the ground appears to be the only other significant layer. Of note was the observation of the crown of a fairly large avalanche the ran down the west face of Leprechaun Ridge. The crown wasn’t there when one of the group was there on 091217. However strong east wind were moving lots of the low density surface snow at that time and we hypothesized that loading associated with those winds onto shallow facetted snow near the ridge crest combined with the rapid warming on the 18th likely resulted in the avalanche. Visibility was limited but no other avalanche activity was observed. Skiing quality was good down to the cut block where the crust made turns a bit of a challenge. Snowing and blowing hard from the east when we left.
Thanks for the obs Craig!
Anna