Avalanche Forecast

South Columbia

Date issued

Apr 23, 2018 - 4:08 PM

Valid until

Apr 24, 2018 - 2:00 PM

Prepared by

cgarritty

Surface instabilities and cornice hazards should be firmly on your radar as you travel. Expect stability to deteriorate over the course of each day.

This is our final regular forecast of the season and will expire on April 25.

Regular season
Tuesday - April 24, 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.

Wednesday - April 25, 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 - April 26, 2018
Alpine

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.

Treeline

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.

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: Loose Wet

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

Daytime warming and sun exposure will promote natural loose wet avalanche activity this week - especially around steep sun-exposed terrain.

Travel and Terrain Advice
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
  • Minimize exposure when the solar radiation is strong, especially if snow is moist or wet.

Avalanche Problem 2: Cornices

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

Weak overnight cooling, warm daytime temperatures and strong sun will be increasing the chance of cornice failures in coming days. Large cornice falls may have potential to trigger large avalanches.

Travel and Terrain Advice
  • Cornices become weak with daytime heating. Minimize your overhead exposure.
  • Give cornices a wide berth when travelling on or below ridges.

Avalanche Summary

Decreasing traffic in the mountains has led to limited avalanche observations over the past few days, however a large (size 2) recent cornice fall from was observed in the north of the region on Sunday. It failed to trigger any slab.

A few natural storm and wind slab releases were observed on Thursday, ranging from size 1-2.5. One of these was a size 2 slab triggered by a loose wet avalanche while the 2.5 wind slab was triggered by natural ice fall on a north aspect at 2200 metres. It featured a 45 cm crown fracture.

Reports from Wednesday included an observation of a natural size 2 cornice release from a north aspect in the north of the region. Numerous natural loose wet avalanches were also observed on sun-exposed aspects in the Monashees.

Observations from just over a week ago showed a pattern of heightened cornice failure activity.

Looking forward, a period of increasing warming, full sun, and warm overnight temperatures will be maintaining elevated chances of cornice and loose wet avalanche activity.

Snowpack Summary

A surface crust is likely to exist on all but north aspects in the alpine and is expected to undergo melt-freeze cycles with daily warming and overnight cooling. Below the surface, about 70-100 cm of mostly settled storm snow overlies another supportive crust existing on all but north aspects above about 2200 metres.

This layer as well as the deeper (down about 80-120 cm) mid-March crust are of limited concern concern after warm temperatures have promoted settlement and bonding in the upper snowpack. Any remaining uncertainty with regard to their strength is generally limited to high north aspects as well as the possibility for triggering with a heavier load, such as a cornice collapse. Cornice collapses become more likely during periods of intense warming.

Deeper persistent weak layers from December and January are considered dormant at this time.

Weather Forecast

Tuesday: Mainly sunny. Light south winds, increasing to strong at ridgetop. Freezing level to 3100 metres with alpine high temperatures around +4. Weak overnight cooling.

Wednesday: Sunny. Light northwest winds. Freezing level rising to 3500 metres by evening and staying steady overnight. Alpine high temperatures around +7.

Thursday: Sunny. Light south winds. Freezing level to 3600 metres with alpine high temperatures around +9.

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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