Avalanche Forecast

South Coast Inland

Date issued

Apr 10, 2018 - 4:14 PM

Valid until

Apr 11, 2018 - 2:00 PM

Prepared by

swerner

Ridgetop winds are strong from the southwest, building reactive wind slabs at upper elevations. Rising freezing levels will weaken the snow surface and increase the likelihood of triggering avalanches.

Regular season
Tuesday - April 10, 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 - April 11, 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.

Thursday - April 12, 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

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?

Reactive wind slabs likely exist at treeline and above on leeward slopes. At lower elevations, loose wet avalanches may occur as the daytime temperature rises.

Travel and Terrain Advice
  • Use ridges or ribs to avoid pockets of wind-loaded snow.
  • Avoid steep slopes when air temperatures are warm, or the solar radiation is strong.
  • Watch for signs of instability such as whumpfing, or cracking.

Avalanche Problem 2: Persistent Slabs

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

A weak layer buried 40 to 70 cm is still surprising people and producing large and destructive avalanches. Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.

Travel and Terrain Advice
  • Pay attention to overhead hazards like cornices, which could trigger persistent slabs.
  • Avoid steep terrain or areas with a thin or variable snowpack.
  • Be aware of the potential for wide propagation due to the presence of buried weak layers.

Avalanche Problem 3: Cornices

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

Cornices are very large and fragile. Give them a large berth while on ridges and avoid traveling underneath them, as they may trigger avalanches on slopes below.

Travel and Terrain Advice
  • Stay well back from cornices.
  • Pay attention to overhead hazards like cornices, which could trigger persistent slabs.

Avalanche Summary

On Monday, a small natural avalanche cycle was observed from southeast aspects around 2300m. Widespread whumphing was observed in a drainage in the north of the region, which was suspected to have been on the late-March weak layer described in the Snowpack Summary. Expect the avalanche hazard to rise through the forecast period with new snow and wind.

Snowpack Summary

Up to 10 cm of new snow overlies moist snow surfaces. At higher elevations, this overlies slabs formed from last weekends snow that fell with strong southwesterly winds. On ridges, cornices are reported to be large and fragile. At low elevations below treeline, recent rain has created moist or wet snow conditions.

A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 50 to 100 cm. This layer is spotty in its distribution. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.

The mid and lower snowpack are well-settled and strong.

Weather Forecast

Wednesday: Mostly cloudy with scattered flurries. New snow 5-10 cm. Ridgetop wind strong from the southwest and freezing levels rising to 1800 m.

Thursday: Mix of sun and cloud. New snow up to 5 cm. Ridgetop wind strong from the southwest and freezing levels 1200 m.

Friday: Yet another blast of winter up high! Heavy snow. Up to 20 cm in the North and up to 40 cm in the South. Ridgetop winds strong-extreme from the southwest with freezing levels near 1500 m.

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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