Avalanche Forecast

Northwest Coastal

Date issued

Apr 16, 2018 - 4:13 PM

Valid until

Apr 17, 2018 - 2:00 PM

Prepared by

mbender

The weather is due to change with snowfall forecast for Wednesday and Thursday. Avalanche danger will gradually increase as the snow starts to accumulate Thursday.

Regular season
Monday - April 16, 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 17, 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.

Wednesday - April 18, 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: Loose Wet

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

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

Travel and Terrain Advice
  • Minimize exposure to sun exposed slopes when the solar radiation is strong.
  • Watch for signs that the snow is heating up such as pin-wheeling or the surface snow becoming moist.
  • Cornices become weak with daytime heating. Give them a wide berth both from above and below.

Avalanche Problem 2: Wind Slabs

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

Sunshine may cause recently formed wind slabs to become more reactive to human triggers.

Travel and Terrain Advice
  • Travel on ridgetops to avoid wind loaded slopes.
  • Use caution when transitioning into wind effected terrain.

Avalanche Summary

Reports from this weekend indicate loose wet activity on steep slopes facing the sun at tree line and in the alpine. These avalanches were reported as size 1-2 and were isolated to the recent surface snow only. Several naturally triggered wind slabs up to size 2 on steep alpine features were reported near Bear Pass on Saturday.

Snowpack Summary

10-20 cm of recent storm snow and strong variable winds have formed wind slabs on a variety of aspects at treeline and above.

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

Bellow these March layers the mid-pack is generally well-settled and strong. However, in the portions of the region with a shallower snowpack, such as the far north, have weak sugary facets near the bottom of the snowpack.

Weather Forecast

TUESDAY:  Mix of sun and cloud. Light southwest wind. Alpine temperature -2. Freezing level 1100 m.

WEDNESDAY: Flurries, accumulation 5-10cm. Light to moderate south wind. Alpine temperature -2. Freezing level 1100 m.

THURSDAY: Periods of snow, accumulation 10-20cm. Moderate south wind. Alpine temperature -1. Freezing level 1200 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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