Avalanche Forecast

Archived

Feb 7th, 2020–Feb 8th, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

The storm will intensify overnight and strong southwest wind combined with new snow will form fresh wind slabs in lee terrain features. Highest snowfall amounts of 20-30 cm are expected in the Coquihalla area.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Friday Night: Snow, accumulation 5-15 cm with highest amounts of 20-30 cm in the Coquihalla area, strong southwest wind, alpine high -4 C, freezing level 1200 m.

Saturday: Mix of sun and cloud, moderate to strong north wind, alpine high -6 C, freezing level 900 m.

Sunday: Mix of sun and cloud, light to moderate northwest wind, alpine high -5 C, freezing level 1000 m.

Monday: Mostly sunny, light to moderate northwest wind, alpine high -4 C, freezing level 1500 m.

Avalanche Summary

No new avalanches were observed on Thursday.

On Wednesday numerous small (size 1) natural slab avalanches were observed below treeline which released within the recent storm snow and were very soft. Several small (size 1) and one large (size 2) loose dry avalanche were reported.

The deep persistent slab avalanche activity observed during last weekend's storm in the northern portion of the region seems to have tapered off. Although the likelihood of triggering has reduced there is still concern for deep releases in that part of the region.

Snowpack Summary

The new snow sits on a variety of surfaces. Extreme southwest wind during the storm last weekend has scoured windward aspects, formed deep loaded pockets in alpine lees and contributed to rapid cornice growth. Below 1900 m, snow overlies a crust.

In the north part of the region (ie. Goldbridge/Duffey/Hurley), a few deep instabilities exist in the snowpack, including a weak basal facet crust complex. This has been the failure plane in ongoing reports of very large, deep persistent avalanches.

The south of the region, including the Coquihalla and Manning areas, currently have no concerns about deeply buried weak layers.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Be alert to conditions that change with elevation and wind exposure.
Carefully evaluate steep lines for wind slabs.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.