Avalanche Forecast

South Columbia

Date issued

Feb 28, 2018 - 4:14 PM

Valid until

Mar 1, 2018 - 2:00 PM

Prepared by

istorm

Storm slabs on steep slopes, wind slabs on lee slopes, and a persistent slab that seems to be "waking up" on southerly slopes. There's lots to think about, and manage!

Regular season
Wednesday - February 28, 2018
Alpine

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.

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.

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

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.

Friday - March 2, 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.

Avalanche Problem 1: Wind Slabs

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

New snow and ongoing strong winds will continue to promote wind slab formation in wind-loaded areas on the leeward side of ridges and on cross-loaded slopes and gulleys. Storm slabs may also be found in sheltered area on steeper slopes and rolls.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Stay off recent wind loaded areas until the slope has had a chance to stabilize.
  • Use caution on open slopes and convex rolls

Avalanche Problem 2: Persistent Slabs

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

An interface buried up to 70cm deep has "woken-up". This problem seems most reactive in south-facing terrain where buried crusts exist.

Travel and Terrain Advice
  • Choose conservative lines and watch for clues of instability.
  • Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.
  • Carefully assess and consider avoiding southerly facing slopes.

Avalanche Summary

Recent avalanche activity has consisted of mainly loose dry sluffing, storm slabs, or wind slabs (skier triggered and skier remote) in the size 1to 2 range. However, we've also received reports of persistent slab avalanches recent accumulations have been the highest. These avalanches, were remotely triggered (from a distance) or naturally occurring. We suspect the buried sun crust buried mid-February is the culprit with those on southerly aspects. Deep persistent avalanche activity has become less frequent over the past week.

Snowpack Summary

Around 20 to 40 cm of recent storm snow is being redistributed into deeper, reactive slabs in wind-exposed terrain. It also covers old surfaces including faceted powder, a sun crust on solar aspects, and surface hoar on shady slopes. Around 50 to 80cm below the surface there's a layer buried mid-February that's a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above. It also seems more of a problem in southern areas of the region.

There are several deeper layers that have shown signs of improving but still remain suspect as low probability - high consequence avalanche problems. I'm talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall, smaller avalanches coming down from above); human triggering is also possible in shallow, rocky terrain.

Weather Forecast

An approaching Low and associated weak front should only bring light snow Wednesday afternoon and overnight with winds backing to the south for the next couple of days.

THURSDAY: Light snow with moderate east winds. Treeline temperatures around -5 to -10 C

FRIDAY: More snow overnight Thursday and possibly into Friday with up to 10 or even 15 cm possible. However, there's significant uncertainty about the just how much new snow will fall. Having said that, highest amounts will be in the south, less as you go north towards Nakusp or Revelstoke. Light to moderate southerly winds.

SATURDAY: trace to a few centimetres of snow, light and variable winds, treeline temperatures of around -10 C.

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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