Avalanche Forecast

North Columbia

Date issued

Apr 8, 2018 - 3:59 PM

Valid until

Apr 9, 2018 - 2:00 PM

Prepared by

ghelgeson

A buried persistent weak layer may roar back to life over the next few days as the freezing level rises and the sun comes out. South facing slopes are especially suspect and are best avoided at this time.

Regular season
Sunday - April 8, 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.

Monday - April 9, 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.

Tuesday - April 10, 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.

Avalanche Problem 1: Persistent Slabs

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

Weak crust and surface hoar 60 to 110 cm below the surface have shown prolonged reactivity since the last storm. South facing features have been the most reactive, a trend that is expected to continue as temperatures increase Monday and Tuesday.

Travel and Terrain Advice
  • Pay attention to overhead hazards like cornices which could trigger persistent slab avalanches.
  • Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.
  • Minimize exposure to steep south-facing slopes where recent storm snow overlies a crust.

Avalanche Problem 2: Storm Slabs

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

5 to 10 cm of snow fell Saturday with moderate southerly wind, which likely formed shallow wind slabs immediately lee of ridge crest. Warming temperatures and brief periods of sun Monday may initiate natural storm slab and loose avalanche activity.

Travel and Terrain Advice
  • Minimize exposure to steep, sun exposed slopes if the strong April sun comes out.
  • Be cautious of sluffing in steep terrain.
  • Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Avalanche Summary

No new avalanche activity to report from Saturday.

On Friday a size 1.5 persistent slab avalanche with a 60 cm crown was skier triggered on a north facing slope at 2000 m. Natural loose dry and loose wet avalanches were observed on north and west facing slopes above 2000 m.

On Thursday warming temperatures initiated large loose wet avalanches to size 3 on south facing aspects between 2100 and 2700 m in the neighboring Glacier National Park. A small shallow wind slab was accidently triggered by a skier on a steep/unsupported east/southeast facing feature at 2200 m too.

Snowpack Summary

5 to 10 cm of new snow fell Saturday with moderate southerly wind. This snow rests on a crust that is present on all aspects below 2000 m, and extends up to about 2500 m on south facing aspects. The storm snow be be sitting on surface hoar on polar aspects (north and east) at upper elevations.

The main concern is the mid-March Persistent Weak Layer (PWL) which is now 60 to 110 cm below the surface. This layer is composed of a crust on all aspects at low elevations. At upper elevations the layer presents as a crust on solar aspects (those that face south and west) and buried surface hoar on polar aspects. The reactivity of this interface has been steadily decreasing and while the likelihood of triggering a deeper persistent slab avalanche is lowering, the consequence of doing so remains high. Solar aspects are expected to be the most suspect as the freezing level begins to rise over the next few days.

Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.

Weather Forecast

Monday, most of BC will receive partly cloudy conditions with a few lingering flurries in the Columbia mountains. A warm system makes landfall Tuesday morning, which should open the door to rain and wet snow into the alpine on Tuesday and Wednesday.

MONDAY: Broken cloud cover, freezing level beginning around 1200 m rising to about 1800 m, light to moderate west/southwest wind, 1 to 4 mm of precipitation possible.

TUESDAY: Scattered cloud cover, freezing level beginning around 1400 m rising to about 2500 m, light to moderate south/southwest wind, trace of precipitation possible.

WEDNESDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 1700 m, light to moderate southwest wind, 2 to 5 mm of precipitation 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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