Avalanche Forecast

Archived

Mar 7th, 2020–Mar 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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary.

This weekend's snow is forming new slabs and loading a buried weak layer. Don't be complacent, as the buried weak layer continues to surprise people. Use caution on sun-exposed slopes when the sky clears.

Confidence

High - The snowpack structure is generally well understood.

Weather Forecast

SATURDAY NIGHT: Mostly cloudy with isolated snowfall, accumulation 2 to 5 cm, light southwest wind, alpine temperature -7 C.

SUNDAY: Mix of sun and cloud with isolated flurries, 2 to 5 cm in the east of the region, moderate southwest wind, alpine temperature -9 C, freezing level 1000 m.

MONDAY: Clear skies, light southwest wind, alpine temperature -7 C, freezing level 1200 m.

TUESDAY: Mix of sun and cloud, light southwest wind, alpine temperature -6 C, freezing level 1200 m.

Avalanche Summary

On Friday, a few more small (size 1.5) avalanches released on the surface hoar layer described in the Snowpack Summary. They occurred on northerly aspects around 2000 m and were 20 to 30 cm deep.

Over the past two weeks, small to large (size 1 to 2) avalanches have released on the surface hoar layer. They have most often released between 1800 and 2300 m on northwest to east aspects. This trend is suspected to continue as this layer slowly gains strength.

Snowpack Summary

Around 10 cm of snow fell in the west of the region and 15 to 30 cm in the east of the region on Saturday. Storm slabs are likely developing as the snow consolidates. The wind remained light to moderate from the southwest, so wind slab formation may be limited to immediate lee features.

The snowfall is loading a touchy layer of feathery surface hoar crystals that is found 30 to 60 cm deep. The layer is most commonly found in open trees (e.g. in this MIN) or sheltered terrain around upper below treeline, treeline, and lower alpine elevations. Check out the latest forecaster blog that offers a deeper dive into these conditions.

The remainder of the snowpack is strong and well-settled.

Terrain and Travel

Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Carefully evaluate steep lines for wind slabs.
Minimize exposure to sun-exposed slopes when the solar radiation is strong.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.