Avalanche Forecast

Sea To Sky

Date issued

Jan 31, 2018 - 3:37 PM

Valid until

Feb 1, 2018 - 2:00 PM

Prepared by

jlammers

New snow and wind will keep the avalanche danger elevated at higher elevations on Thursday.

Regular season
Thursday - February 1, 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

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.

Friday - February 2, 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.

Saturday - February 3, 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

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.

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.

Avalanche Problem 1: Wind Slabs

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

New snow and wind on Wednesday night are expected to form new wind slabs in higher elevation lee terrain. This new snow overlies older storm slabs which are gaining strength but may remain sensitive to human triggering in steep, unsupported terrain.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation.
  • The recent snow may now be hiding stormslabs that were easily visible before the snow fell.

Avalanche Problem 2: Cornices

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

Recent heavy snowfall and high winds have formed fragile new cornices. These monsters may surprise with nasty consequences. Use extra caution around ridge crests.

Travel and Terrain Advice
  • Give cornices a wide berth when travelling on or below ridges.
  • Falling cornices may trigger large avalanches on the slopes below.

Avalanche Summary

As recent storms have tapered-off, so has natural avalanche activity. That said, explosives control on Tuesday triggered lingering storm slabs at treeline and above - mostly in the size 1.5-2 range. The exception was a size 3 slab that was explosives-triggered on a southwest facing alpine slope.

Looking forward, new snow and wind on Wednesday night is expected to promote a new round of wind slab activity in higher elevation lee terrain.

Snowpack Summary

Monday's continuing storm brought another 30-40 cm of new snow to the surface above about 1600 metres with depths that increase with elevation. At treeline and below light amounts of recent snow now overlie a melt-freeze crust. At higher elevations, extreme southerly winds have scoured the new snow from windward aspects and formed deep deposits and cornices in leeward terrain. Including the new snow, storm snow totals since mid-January have reached about 170 cm. Where they haven't been blown away by the wind, these accumulations sit on a crust from mid-January that shows good signs of bonding to the overlying snow.

Other deeper layers in the snowpack include a crust that was buried in early January (now 230-280 cm below the surface) and another crust which was buried in mid-December. Although explosive control work triggered storm slab avalanches that "stepped down" to both of these crusts last week, they are expected to have formed an improved bond with the overlying snow in most areas. With that said, a heavy trigger like a cornice release may still carry the risk of stepping down to deeper layers on isolated features.

Weather Forecast

Wednesday Night: 6-10cm of new snow / Moderate to strong southwest winds / Freezing level at 800m

Thursday: 3-5cm of new snow / Light southwest winds / Freezing level at 900m

Friday: 8-10cm of new snow / Light southwest winds / Freezing level at 1200m

Saturday: Light flurries / Light and variable winds / Freezing level at 1200m

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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