Avalanche Forecast

Northwest Coastal

Date issued

Apr 22, 2018 - 3:56 PM

Valid until

Apr 23, 2018 - 2:00 PM

Prepared by

jsmith

Avalanche danger will increase as the temperatures rise throughout the week.

Regular season
Sunday - April 22, 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

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.

Monday - April 23, 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

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.

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.

Avalanche Problem 1: Wind Slabs

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

Lingering wind slabs may still be reactive to human triggers in wind affected terrain at treeline and above.

Travel and Terrain Advice
  • Travel on ridgetops to avoid wind loaded slopes.
  • Avoid areas that look freshly loaded with snow; especially convex features below ridgetops.
  • Use caution when transitioning into wind affected terrain.

Avalanche Problem 2: Loose Wet

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

When the sun comes out it will quickly weaken the surface snow and cause loose wet avalanching on steep solar slopes.

Travel and Terrain Advice
  • Watch for signs that the snow is heating up such as pin-wheeling or the surface snow becoming moist.
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Avalanche Problem 3: Cornices

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

Sunshine and warming temperatures will increase the likelihood of cornice fall.

Travel and Terrain Advice
  • Cornices become weak with daytime heating. Give them a wide berth both from above and below.
  • Falling cornices may trigger persistent weak layers deeper in the snowpack.

Avalanche Summary

Several very large deep persistent slab avalanches(size 3-4) which were triggered by cornice failures and several natural wind slabs up to size 2.5 were reported near Bear Pass on Saturday. Avalanche reports have been limited due to very few information sources this time of year. If you have been out, please post your observations on the Mountain Information Network. (MIN)

Snowpack Summary

Cornices are large and when they fail there is the potential to trigger large avalanches on deeply buried weak layers. Lingering wind slabs may still be reactive to human triggers on leeward slopes below ridgetops.

In the south of the region, two layers of surface hoar are buried early-March and mid-March are approximately 70-100 cm deep and most prominent on north to east aspects. Further north, these layers are around 40 cm deep.

Below these March layers the mid-pack is generally well-settled and strong. However in the far north of the region there are weak sugary facets near the bottom of the snowpack.

Weather Forecast

MONDAY: Mostly cloudy. Strong southwest wind. Alpine temperature +5. Freezing level 1600 m.

TUESDAY: Mix of sun and cloud. Moderate west wind. Alpine temperature +3. Freezing level 1400 m.

WEDNESDAY: Sunny. Light west wind. Alpine temperature +10. Freezing level 3000 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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