Remain disciplined in terrain selection. Caution Nass Valley region where a very large wind slab avalanche was triggered & hazard is CONSIDERABLE. Watch for signs of instability: recent avalanches, shooting cracks, hard/soft wind slabs with hollow sounds, whumpfs or cracking.
Wind slabs will likely remain reactive to human triggering, especially where they sit atop a surface hoar layer. Very deep wind slabs (up to 1.5meters thick) have been reactive in recent days. Recent winds have been highly variable. Reverse loading from east winds, cross-loading and buried wind slabs may be present.
A weak layer of surface hoar is buried 40-70cm below recent storm snow. A surface hoar layer has been reactive in the Nass Valley as well as in the Shames area, and likely exists in most sheltered reeling and below treeline regions. A crust that was buried in early December is now down 90-200 cm and counting. Around this crust are facets and potentially surface hoar in sheltered areas. Step-down avalanches are a significant possibility where a small wind slab or cornice fall may trigger a large and destructive avalanche.
The next series of weather systems influences the region late in the day Tuesday bringing a few days of stormy conditions with light snow and moderate to strong winds. Precipitation amounts with Tuesday night / Wendesday storm vary with models.
Monday night: Cloudy with clear periods. Alpine low temperatures near - 5C and freezing levels valley bottom. Ridgetop winds light to moderate from the west.
Tuesday: Mainly cloudy with isolated flurries in the afternoon, trace to 10cm new snow late in the day, alpine high temperatures near -4C and freezing levels valley bottom. Ridgetop wind moderate to strong from the south/southwest.
Wednesday: Mainly cloudy with snow flurries, 5-15cm new snow. Alpine high temperatures near -2C and freezing levels valley bottom. Ridgetop winds moderate to strong from the southwest shifting southeast.
Thursday: Mainly cloudy with snow flurries, trace-5cm new snow. Alpine high temperatures near -2C and freezing levels valley bottom. Ridgetop moderate to strong from the southwest shifting southeast.
On the 27th an accidentally triggered very large (size 3) avalanche from the Beaupre riding area north of terrace. We are so glad everyone appears to be ok. One photo shared illustrates dense wind slabs and they report a slab of 1-1.5m (3-5 feet) thick. While they don't mention a failure plane, we are curious if there was surface hoar involved since this MIN & this MIN from the 21st in Beaupre (Nass Valley) region highlight touchy conditions on surface hoar with multiple remote triggered (size 1-2) avalanches. Father to the north, a very large (size 3.5) wind slab was reported to have released naturally on the 25th on a southwest aspect and technicians suspect this windslab failed on surface hoar following east winds. Both of these very large avalanches are illustrative of the high consequences of large wind slabs, particularly when they sit on top of a weak layer.
At the height of the Christmas Eve storm and for the following days, widespread large and very large avalanches were reported. Reverse loaded and cross-loaded wind-slabs from east winds created reactive windslabs on west and south west aspects which produced large (size 2) and very large (up to size 3.5) avalanches naturally and when tested with explosives.
Please consider sharing your observations with the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter!
No new snow in recent days with moderate winds across exposed ridgecrests and in the alpine. Deep wind slabs may remain reactive from the Christmas Eve storm, especially where they sit on top of surface hoar. Look for signs of wind effect: scoured surfaces, sastrougi, reverse wind loading, cross loaded gullies and deep wind slabs (100-150cm deep) in lee features.
Significant variability exists with buried weak layers. A zone of reactivity has been noted in the Beaupre riding area in the Nass Valley - which may be due to a deeper Surface Hoar layer in this zone coupled with recent wind slabs. Recent 40-60cm recent snow is settling rapidly. In sheltered areas, this new snow may sit atop a crust or surface hoar layer that formed before this recent storm. Shames has reported this layer down 40-60cm. A crust that was buried in early December is now down 90-120cm plus and has facets and potentially surface hoar in sheltered areas. Storm slabs may step-down to this layer.
The early-November crust is buried around 170-200 cm at treeline and deeper in the alpine. This crust may have weak and sugary facets above it in parts of the region. This layer is currently dormant but remains on our radar.
