Observation: Public
Observation Details
Name:
Mark AllenObservation Date:
December 22, 2020Submitted:
December 22, 2020Zone or Region:
East NorthActivity:
Skiing/SnowboardingLocation:
North Cascades-East Slopes North-Cutthroat and Pine CreekObserved Avalanches
Did you observe any avalanches?
YesAvalanche Type:
OtherSize:
Size 2: Could bury, injure, or kill a personElevation:
7000ft + Alpine start zones running to into the valleyAspect:
SWComments:
Today, I observed a dozen or more D2 to D2.5 from the recent solstice precipitations in the last 24-48rs. Nearly all of the avalanches originated in classic alpine start zones in connected terrain, solar aspects, ran into the valleys, however rarely fully completed their tracks. The propagation and connected crowns would point to the failure being associated with the buried Early-Dec persistent weak layer reported in the forecast however the crows were not observed or confirmed. On a few occasions, the bed surfaces reloaded from wind deposit and in even fewer cases ran a second time in the last 24hrsPhoto:
Signs of Unstable Snow
Did you see shooting cracks?
Yes, IsolatedDid you experience collapsing or whumpfing?
NoObservations
Snowpack: At 6000ft the snow depth was 220cm Near tree line (NTL), and in the alpine, the storm snow was wind affect near the ridges. In the test pit, the solstice interface was represented as a resistance change. At lower elevations ( 5000ft) the solstice interface is a more distinct 2cm crust. In either case the solstice interface produced sudden results with easy compressions or on isolation. The deeper Early-Dec interfaces/crust down 85cm was expressed by a thin 2-3mm layer of 1mm facets (NSF) that failed suddenly and cleanly with moderate compression.
Many travelers were limited to a few concentrated areas below tree line or near tree line. This was mostly due to labor of travel in the deep snow and deep snow on the HWY. Collapses and wumphs have subsided. Travelers and have not tested the alpine slopes. My uncertainty lies in the alpine-shaded aspects and the distribution of the Early Dec facets.
In summary the layers of observed concern are the buried Early-Dec persistent weak layer 85cm down. This layer is still reactive in pit test and appear to be associated with recent large avalanches with significant propagation. The most reactive layer to a travellers was the wind slabs above 6000ft near the crest on South-East aspects.
Have a safe holiday and please and heed the warning signs.
Mark Allen -NWAC Pro Observer/ East Slopes North
Media
