Avalanche Forecast

Northwest Inland

Date issued

Mar 26, 2018 - 4:54 PM

Valid until

Mar 27, 2018 - 2:00 PM

Prepared by

cgarritty

Storm slabs have proven consistently reactive over the past few days and forecast strong winds will be promoting new slab formation on Tuesday. Stick to supported slopes in your search for sheltered powder.

Regular season
Monday - March 26, 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

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.

Tuesday - March 27, 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 - March 28, 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

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: Storm Slabs

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

30-40 cm of recent snow has been settling into a slab over melt-freeze crust in most areas as well as surface hoar on high shaded aspects. Thicker and more reactive slabs are likely to be found on north to east aspects in wind-exposed terrain.

Travel and Terrain Advice
  • Be increasingly cautious and watch for patterns of wind loading if you enter wind-affected terrain.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.
  • Watch for signs of instability like shooting cracks or recent avalanches.

Avalanche Summary

Reports from Sunday again included numerous observations of ski cutting producing size 1.5 storm slab releases on small rolls. These slabs were failing at an upper storm interface before stepping down to the full depth of our recent storm snow (about 40 cm). Conservative terrain selection is likely to have limited the size of these results.

On Saturday, ski cutting on convex rolls below treeline produced size 1.5 slabs in the recent storm snow down 30 cm deep. These failed over the widespread melt-freeze crust and gathered substantial mass as they traveled downslope.

Snowpack Summary

Up to 40 cm of storm snow now overlies a range of old snow surfaces, including two layers of surface hoar existing on shaded aspects at high elevations as well as a melt-freeze crust on all aspects at treeline and below. This storm snow has been showing a poor bond to the shallowest of these buried weak layers, down about 40cm. Recent strong winds have redistributed the new snow into thicker and likely more reactive wind slabs on a range of aspects wind-exposed terrain. Southwest winds have been the most recent.

Deeper in the mid-pack, layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist from mid- and late-February and a surface hoar/ crust layer from January is buried around 150 to 200 cm. Near the bottom of the snowpack, sugary facets exist in colder and dryer parts of the region, such as the far north.

Weather Forecast

Tuesday: A mix of sun and cloud with isolated flurries and a trace of new snow. Strong to extreme west winds. Freezing level to 900 metres with alpine high temperatures around -6.

Wednesday: A mix of sun and cloud. Moderate to strong west winds. Freezing level to 1000 metres with alpine high temperatures around -6.

Thursday: Mainly sunny. Light variable winds. Freezing level to 900 metres with alpine high temperatures around -6.

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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