Avalanche Bulletin - Waterton Lakes National Park - Thu Jan 24, 2019

Issued: Wed Jan 23, 2019 08:58
Valid Until: Sat Jan 26, 2019 17:00

New windslabs may propagate further than expected on buried suncrust and surface hoar layers. [AG]

Public Avalanche Forecast
Danger Ratings: Thursday alpine treeline below treeline
alpine: 2 - Moderate
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
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
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.
Forecast
Forecast Friday Saturday
alpine View Alpine Danger Rating Trend 2 - Moderate 3 - Considerable
treeline View Treeline Danger Rating Trend 2 - Moderate 2 - Moderate
below treeline View Below Treeline Danger Rating Trend 1 - Low 2 - Moderate
Confidence: Moderate - Freezing levels are uncertain on Saturday
High The forecast is based on high-quality information and the nature of the issue makes it possible to render a solid judgement. A 'high confidence' rating does not imply fact or complete certainty however, and such judgements still carry the risk of being wrong.
Moderate The information used to produce the forecast is credibly sourced and plausible, but it is not of adequate quality or sufficiently corroborated to warrant a higher level of confidence.
Low The credibility or plausibility of the information used to produce the forecast is questionable, or the information is too fragmented or poorly corroborated to make solid judgements, or there are significant concerns regarding problems with the sources.
Past 24 hour weather
Station Maximum (°C) Minimum (°C) Snowfall (cm) Snow Pack (cm) Wind speed Ridgetop wind direction
Little Prairie 1650m Not Available Not Available Not Available Not Available Not Available Not Available
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.
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.
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.
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.
Extreme
  • Avoid all avalanche terrain.
  • Natural and human-triggered avalanches certain.
  • Large to very large avalanches in many areas.

Problem 1: Wind Slabs

Which Elevation?
Which Elevation? alpine, treeline
Which Slopes?
Which Slopes? southeast, northeast, east, north, south, southwest
Chance of Avalanches?
Chance of Avalanches? possible - likely
Expected Size?
Expected Size? small - large

Southwest through northwest winds have formed thin wind slabs over a crust / surface hoar layer and may propagate farther than expected. Dig down and investigate the bond of new snow before committing to your line.

Travel and Terrain Advice

  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.

Problem 2: Deep Persistent Slabs

Which Elevation?
Which Elevation? alpine, treeline, below treeline
Which Slopes?
Which Slopes? north, northwest, southwest, west, south, southeast, east, northeast
Chance of Avalanches?
Chance of Avalanches? unlikely - possible
Expected Size?
Expected Size? large - large

This layer likely requires a large trigger. Be cautious when transitioning from thick to thin snowpack areas

Travel and Terrain Advice

  • Avoid steep convexities or areas with a thin or variable snowpack.
Problem Glossary
Dry Loose
  • Are usually small, but may gain significant mass on long steep slopes.
  • Are typically limited to steep terrain (40+ degrees).
  • Stabilize soon after a storm, usually within a few days.
Dry Loose avalanches are best managed by:
  • Avoiding terrain traps and large steep slopes until the surface has stabilized.
  • On large steep slopes, occasionally move across the fall line to avoid being caught by your own sluffs from above.
Wet Loose
  • Are more powerful than dry loose avalanches due to their higher density.
  • Are often limited to sunny slope aspects.
  • Are commonly confined to the warmest part of the day.
Wet Loose avalanches are best managed by:
  • Avoiding start zones and avalanche paths when the snow becomes moist from daytime heating, from rain, or does not freeze overnight.
Wind Slabs
  • Vary in size from small to medium.
  • Occur on steeper lee and cross-loaded portions of slopes (typically 35+ degrees).
  • Are often limited to specific terrain features such as lee ridge-tops.
  • Can often be recognized by the appearance of the snow surface, changes in surface snow hardness, hollow, drum-like sounds and/or shooting cracks.
  • Winds that vary in strength and direction can produce complex and unexpected wind slab patterns.
  • Stabilize fairly soon, usually in a few days to a week.
Wind slabs are best managed by:
  • Recognizing and avoiding areas where wind slabs have formed, until they have stabilized.
Storm Slabs
  • Vary in size from small to very large.
  • May be soft slabs, fooling people into underestimating slab potential.
  • Tend to occur on moderately steep slopes (35+ degrees).
  • May occur in all terrain, but are larger and more frequent in the alpine.
  • Stabilize soon after a storm, usually within a few days.
Storm slabs are best managed by:
  • Conservative terrain choices during and after storms until the storm snow has stabilized.
Wet Slabs
  • Involve wet layers in the snowpack, typically including deeper layers.
  • Tend to be large.
  • Occur when water forms or penetrates below the surface of the snowpack.
Wet slabs are best managed by: 
  • Avoiding start zones and avalanche paths when the snow becomes wet from daytime heating, rain, or lack of an overnight freeze.
Persistent Slabs
  • Slide on buried persistent weak layers, which often form during clear periods and may involve deeper layers from multiple storms.
  • Vary in size from medium to very large and may cross terrain barriers to involve multiple slide paths.
  • May occur on very gentle terrain, even slopes of 20 degrees or less.
  • May be localized to specific elevations, aspects, or regions.
  • There are often no visible signs of persistent slab instability.
  • Lack of avalanche activity and lack of danger signs are NOTreliable indicators of stability.
  • Compression tests and Rutschblock tests may locate persistent weak layers.
  • Stabilize slowly, tending to persist for several weeks or longer.
  • Often have dormant periods, becoming active again when the weather changes.
  • Are prone to lingering pockets of instability that persist long after most areas have stabilized.
  • Tend to release above the trigger, making it difficult to escape.
  • Are often triggered remotely from a long distance away.
Persistent slabs are best managed by:
  • Very conservative terrain choices.
  • Allow extra time for persistent slabs to stabilize and use a very cautious approach to new terrain. Be especially cautious after storms or during warming periods.
Deep Persistent Slabs
  • Slide on deeply buried persistent weak layers, which often form during clear periods or rain-on-snow events early in the season.
  • Involve thick, hard slabs, sometimes the entire snowpack.
  • Tend to be very large, commonly cross terrain barriers to involve multiple slide paths.
  • Tend to occur on larger slopes of moderate steepness, typically 30-40 degrees.
  • May be localized to specific elevations, aspects, or regions.
  • There are often no visible signs of persistent deep slab instability.
  • Lack of avalanche activity and lack of danger signs are NOT reliable indicators of stability.
  • Stabilize slowly if at all, persisting for months and often the entire season.
  • Dormant persistent deep slab instabilities often become active again when the weather changes, especially after storms or with warm spring weather.
  • Tend to release above the trigger, making it difficult to escape.
  • Are often triggered remotely from a long distance away.

Deep persistent slabs are best managed by:

  • Very conservative terrain choices and a very cautious approach to new terrain.
  • Be especially cautious after storms or during warming periods.
Cornices
  • May trigger large slab avalanches on relatively stable slopes below.
  • Are often associated with recent wind loading and/or temperature changes.
  • Can be triggered from ridges, sometimes breaking surprisingly far back onto ridge tops.

Cornices are best managed by:

  • Approaching corniced ridges cautiously.
  • Avoid travelling on or near overhanging cornices and limit time spent exposed to slopes below cornices, especially soon after wind events and during periods of warming temperatures.
Forecast Details

Weather Forecast

Thursday: Mainly cloudy with isolated flurries. Moderate west winds. Alpine high -7

Friday: Cloudy with sunny periods and isolated flurries. Moderate west winds. Alpine high -7

Saturday: Mainly cloudy with isolated flurries. Moderate southwest winds. Freezing level is uncertain with models predicting anywhere between 1500 and 2200m

Snowpack Discussion

30cm of recently wind affected snow has gradually loaded either a suncrust below 2000m on solar aspects or spotty surface hoar in sheltered areas between 1600 and 1900m. This may be a problem layer when we see more snow. The midpack is strong in deep snowpack areas, but the facets lingering at the bottom remain a concern in thinner areas.

Avalanche Activity Discussion

Skier controlled wind slabs to 1 were reported in the Castle region yesterday.

For More Details

Emergency: 911
Forecasters: (403) 859-5140

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