Cross and reverse wind loading from north winds Monday evening resulted in a large avalanche cycle in the alpine around the Churchill Range. Normally shallow alpine slopes could be primed to avalanche with a hard wind slab sitting on faceted snow.
North winds have caused reverse loading wind slabs down into the tree line. This seams to be more prominent north of Tangle Hill. It is especially a concern where a hard wind slab sits over weak faceted snow. Listen for a hollow sounding snowpack.
A persistent slab sits over two different layers depending on elevation and aspect. Below 1950m, a faceting rain crust is roughly 40-60cm down. Above 1950m, a buried surface facet layer down 20-30cm is the primary concern.
Weak facets and depth hoar are at the base of the snowpack.
Wednesday
Cloudy with sunny periods.
Precipitation: Nil.
Alpine temperature: High -9 C.
Light ridge wind.
Freezing level at valley bottom.
Thursday
Mainly cloudy with isolated flurries.
Precipitation: Trace.
Alpine temperature: Low -13 C, High -8 C.
Ridge wind southwest: 10 km/h.
Freezing level at valley bottom.
North winds have built cross and reverse wind slabs into tree line. The mid snowpack is faceted with two notable persistent weak layers. A buried facet interface is down 20-30cm. A faceting crust is down 40-60cm below 1950m. Basal facets and depth hoar can be found at the base of snowpack.
Several large avalanches were observed around the Churchill Range up to sz 2.5 and running to ground. These are likely the results of normally shallow thin wind blown slopes being loaded from north winds on Monday evening.
