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Avalanche Forecast

Archived

Jan 13th, 2020–Jan 14th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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.

Regions

Kootenay Boundary.

The snowpack needs time to adjust to all of the new snow & wind. Strong north wind may have formed fresh slabs in unusual locations at all elevations. We all need to scale the terrain choices back to simple well-supported features for the next few days.

Confidence

Low - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

After a stormy period it looks like the intensity of the weather will back off for the next few days with quite cold temperatures, dribs and drabs of snow and a consistent wind out of the southwest.

MONDAY NIGHT: Freezing level at valley bottom, light to moderate southwest wind, no significant precipitation expected.

TUESDAY: Scattered cloud cover, freezing level at valley bottom, light to moderate southwest wind, trace of snow possible.

WEDNESDAY: Scattered cloud cover at dawn clearing through the day, freezing level at valley bottom, moderate to strong southwest wind, trace of snow possible.

THURSDAY: Broken cloud cover, freezing level at valley bottom, light to moderate southwest wind, 2 to 8 cm of snow possible.

Avalanche Summary

Both natural and explosive controlled avalanches up to size 2.5 were observed Monday on all aspects above 1800 m. Loose avalanches to size 1.5 were also widely reported.

On Sunday the bulk of the avalanche activity was limited to loose dry avalanches but a spooky avalanche was remote triggered by a group of skiers, more details and photos in this MIN report.

On Saturday, numerous large (size 2) storm slab avalanches were triggered by explosives. Several small (size 1) and large (size 2) storm slab avalanches were triggered by skiers. A few small (size 1) natural storm slab avalanches were reported.

Snowpack Summary

The storm of the last days brought up to 60 cm of snow which fell with moderate to strong southwest wind before winds switched to the north/northeast Sunday night. The resulting wind fueled storm slabs likely remain sensitive to human triggers, particularly in exposed lee terrain features. More recent snow might hide slabs and make it trickier to navigate around them.

Deeper in the snowpack, a few layers of weak and feathery surface hoar may still be found around 70 to 130 cm deep. It is unclear whether or not they are still problematic and if so, how long they will be so for. 

The base of snowpack is also weak in parts of the region, where it consists of sugary faceted snow around a melt-freeze crust. Until these weak layers can be ruled out, best to travel conservatively.

Terrain and Travel

  • Give the new snow several days to settle and stabilize before pushing into bigger terrain.
  • Avoid freshly wind loaded terrain features.
  • Avoid convexities as well as steep, open and/or sparsely treed slopes at and below treeline.
  • Avoid lingering or regrouping in runout zones.

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.

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.