The snowpack is complex with numerous concerning avalanche problems. As we leave an active stormy period, conservative terrain choices are recommended to handle these tricky conditions.
Strong to extreme wind from the west coupled with moderate amounts of new snow has left unstable wind slabs at upper elevations. East winds Wednesday night into Thursday have allowed wind slabs to form on all aspects. Wind slab avalanches in motion could step down to buried weak layers and release very large persistent or deep persistent slab avalanches.
30 to 60 cm of settled snow rests above a widespread layer of surface hoar that has produced numerous avalanches over the past week. These slabs have been most sensitive to triggering at treeline, which is a setup that can catch us off guard.
Recent loading from new snow and wind has aggravated the deep persistent slab problem. Some very large and destructive avalanches have been sporadically failing on deeply buried weak layers, predominantly on north through east aspects in the alpine. Cornice falls are a likely trigger for these slabs.
One last pulse Thursday night, and then we’re into a clearing trend for the weekend.
THURSDAY NIGHT: Freezing level at valley bottom, moderate southwest wind, 1 to 5 cm of snow.
FRIDAY: A few clouds, freezing level at valley bottom, light south wind, no significant precipitation expected.
SATURDAY: Clear skies, freezing level at valley bottom, light variable wind, no significant precipitation expected.
SUNDAY: Clear skies in the morning becoming more cloudy after lunch, freezing level at valley bottom, light wind initially with increasing wind out of the west/northwest throughout the day, no significant precipitation expected.
Over the past few days there have been reports of wind slab, persistent slab (failing on the February 19 surface hoar layer), and deep persistent slab (failing on basal facets) avalanches. This pattern highlights how current stormy weather is aggravating multiple weak layers in the snowpack.
On Wednesday a cornice failure in the Kispiox initiated a size 3 wind slab avalanche on a northeast facing feature at 1600 m that cleared out large timber in the valley. The recent storm snow was sensitive to human triggering, even in low angle terrain, running on the March 1st surface hoar. A few shallow natural wind slabs were also observed in steep terrain.
Reports from Tuesday suggest wind slab avalanches occurred naturally in alpine terrain, while at treeline elevations several size 2-2.5 persistent slab avalanches released naturally and with artificial triggers. These slabs failed on the Feb 19 surface hoar layer on north and east aspects.
Size 1 human triggered avalanches on the Feb 19 surface hoar layer have been reported almost daily since last Thursday. These have typically been 30 cm thick on a range of aspects.
Cornice falls have been a common trigger for wind slabs on the slopes below, and last Friday a cornice fall triggered a size 3.5 deep persistent slab on a northeast facing slope at 1800 m.
The Wednesday into Thursday night storm produced 5 to 25 cm of new snow with the deepest accumulations being found in the south accompanied by strong east/southeast wind. Previously, extreme wind from the southwest, west, and northwest has hammered open terrain, scouring some slopes and forming wind slabs on other slopes. Another 5-10 cm of snow is expected to fall Thursday into Thursday night. Fresh storm slabs are likely forming.
Loading from new snow and wind has made several persistent weak layers problematic over the past week. A combination of surface hoar and sun crust layers were buried on February 19 and currently sit 30-60 cm below the surface that seem to be most sensitive to human triggering at treeline elevations. A couple of weak layers that formed in January are buried in close proximity to one another 80-140 cm below the surface. Below that, an early season crust/facet layer lurks at the base of the snowpack.
