Avalanche Forecast

Bits of storm continue to trickle into the region

WEDNESDAY NIGHT: Freezing level around 1200 m, strong southwest wind, 1 to 5 cm.

THURSDAY: Overcast, freezing level around 1100 m, strong southwest wind, 5 to 10 cm of snow with another 5 to 10 cm Thursday night.

FRIDAY: Broken cloud cover, freezing level holding around 1000 m, moderate southwest wind in the morning, light variable wind in the afternoon, 1 to 5 cm of snow.

SATURDAY: Clear skies, freezing level starting at valley bottom rising to around 1000 m, light north wind, no snow expected.

We're short on observations that depict the change in conditions since the storm entered the forecast area and there was no new activity to report from Tuesday. On Monday in the neighbouring Northwest Coastal region in the Ningunsaw zone a natural cornice failure resulted in a very large (size 3.5) deep persistent slab avalanche on a south/southeast facing feature. A skier triggered size two avalanche was reported from a southeast facing feature at 1600 m, the avalanche ran on the Feb 19th surface hoar. On Sunday human triggered avalanches to size 2 were also failing on the February 19th surface hoar, crowns were 10 to 60 cm in depth.

On Saturday storm slabs resting on surface hoar failed naturally and were sensitive to skier triggering producing slabs up to 60 cm in depth. These slabs seem to be more sensitive at and below treeline which is the reverse of how we normally think about avalanche hazard.

Some very large and destructive avalanches have been sporadically running on deeply buried weak layers near the bottom of the snowpack, predominantly on north through east aspects in the alpine. Last Tuesday, a natural size 2.5 was observed. It is suspected to have started as a wind slab in a thin rocky area before stepping down. Last Monday, two deep persistent slab avalanches size 2-3 were triggered from thin snowpack areas by very large loads pushed by snowcats. 

30 to 90 cm of snow now overlies the Feb 19 surface hoar in sheltered locations and a sun crust on solar aspects with the deeper slabs being found in the north of the region. The alpine has been heavily wind affected as evidenced by this MIN submission. The surface hoar may be very sensitive to human triggering at lower elevations which is a bit different setup than we're used to.

There are few different persistent weak layers (PWL's) we're watching in the mid and lower snowpack. A patchy layer of small surface hoar crystals and a sun crust both from early February are now 40 to 100 cm deep. A couple of weak layers that formed in January are buried in proximity to one another 80-140 cm below the surface. Below that, an early season crust lurks at the base of the snowpack. Some large avalanches have been triggered on these layers, usually during periods of rapid loading by new snow or wind and by large loads or from thin, rocky areas. We're now in another one of those periods that could wake up the deep slab as we get 5 to 10 cm of snow and strong southwest wind consistently through Friday.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
• Storm slabs in motion may step down to deeply buried weak layers resulting in very large avalanches.
• The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.