Avalanche Forecast

Kootenay Boundary

Date issued

Feb 26, 2018 - 6:08 PM

Valid until

Feb 27, 2018 - 2:00 PM

Prepared by

ghelgeson

30 to 60 cm of snow is slowly coalescing into a slab above the mid-February persistent weak layer that has recently been sensitive to human triggering. Watch for the formation of fresh wind slabs at upper elevations too.

Regular season
Tuesday - February 27, 2018
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Wednesday - February 28, 2018
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Thursday - March 1, 2018
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Avalanche Problem 1: Wind Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

A few cm of snow and potentially strong west/southwest winds will create fresh wind slabs in many areas in the alpine as well as open areas at lower elevations. Watch for triggering in the lee of ridge crests and convexities.

Travel and Terrain Advice
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Fresh snow Tuesday may hide windslabs that formed over the weekend.
  • Be very cautious as you transition into wind affected terrain.

Avalanche Problem 2: Persistent Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

A persistent weak layer buried up to 60 cm below the surface may be sensitive to human triggering.  Start with simple terrain and gather information before thinking about more committing objectives.

Travel and Terrain Advice
  • Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.
  • Start with conservative lines and watch for clues of instability.
  • If triggered, wind slab avalanches in motion may step down resulting in large avalanches.

Avalanche Summary

On Sunday storm slab avalanches were susceptible to both skier triggering and explosive control work to size 2. Storm slabs were reported from an east facing slope at 2025 m and northeast through northwest facing slopes between 1900 and 2100 m. In the southern portion of the neighboring South Columbia region a skier triggered size 2 avalanche was reported from a southwest facing slope at 1550 m. The avalanche had a crown 40 to 60 cm in depth and ran on the mid-February weak layer.

On Friday and Saturday storm slabs were triggered by skiers and explosives at treeline and alpine elevations, 10 to 25 cm deep.

Snowpack Summary

Two successive storms over the weekend produced 10 to 40 cm of new snow accompanied by wind out of the southwest, west and northwest. 30 to 60 cm of snow now rests on the mid-February weak layer that is composed of facets, surface hoar and a sun crust on solar aspects.

Deeper in the snowpack weak layers that formed in January and December are gradually gaining strength. Several surface hoar and facet layers are buried 1 to 2 m below the surface and there is a crust/ facet interface near the base of the snowpack. No avalanches have been reported on these layers for the past two weeks and snowpack tests are showing improved bonding. Despite these signs, avalanche professionals are still treating these layers with respect and being cautious around shallow start zones and big avalanche paths.

Weather Forecast

A weak upper trough Tuesday should deliver a small shot of precipitation and wind before a vigorous low makes landfall on Wednesday. This system may push into the Kootenay Boundary Wednesday evening. Unfortunately the weather models cannot seem to agree on a solution with regard to track and intensity but there will likely be less uncertainty as we get closer to Wednesday. Stay tuned for more details.

TUESDAY: Broken cloud cover, freezing level beginning at valley bottom rising to around 700 m in the afternoon, moderate to strong west/southwest wind, 1 to 5 cm of snow.

WEDNESDAY: Overcast, freezing level rising to around 1100 m in the afternoon, potentially strong to extreme south/southwest wind, latest model run shows about 10 cm of snow. Stay tuned for more details.

THURSDAY: Overcast, freezing level around 1500 m in the afternoon, light to moderate south/southeast wind, 1 to 5 of snow possible.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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