Avalanche Bulletin - Banff, Yoho, and Kootenay National Parks - Mon Jun 24, 2019

Issued: Sun May 05, 2019 17:33
Valid Until: further notice

Regular avalanche forecasts are now finished. Use our weather stations, the ACMG Mountain Condition Reports, and Mountain Information Network to stay up to date on current conditions, or call Visitor Safety at 403-762-1470 with specific questions. [CJ]

Public Avalanche Forecast
Spring Conditions:  Sunday
Spring Conditions

The avalanche danger is variable and can range from Low to High. Travelling early in the day is recommended, as conditions can change rapidly in short periods of time due to daytime warming. Pay careful attention to the integrity of surface crusts formed overnight and rising air temperatures during the day. Dry slab avalanche danger may also exist during spring snow storms.

Past 24 hour weather
Station Maximum (°C) Minimum (°C) Snowfall (cm) Snow Pack (cm) Wind speed Ridgetop wind direction
Simpson 2115/2320m Not Available Not Available Not Available Not Available Not Available Not Available
Bow Summit 2040m Not Available Not Available Not Available Not Available Not Available Not Available
Sunshine 2200m 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
Which Slopes?
Which Slopes? north, northeast, east
Chance of Avalanches?
Chance of Avalanches? possible
Expected Size?
Expected Size? small - large

Any significant storms or increased winds will redistribute soft snow in the alpine and form wind slabs in lee areas. Watch for wind loading when entering steeper, more committing ski lines or climbing alpine routes.

Travel and Terrain Advice

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Problem 2: Wet Loose

Which Elevation?
Which Elevation? alpine, treeline
Which Slopes?
Which Slopes? southwest, south, southeast, west
Chance of Avalanches?
Chance of Avalanches? likely
Expected Size?
Expected Size? small - small

If the sun comes out for any length of time or daytime temperatures rise above freezing, expect loose wet avalanches out of steep terrain. Cornice failures will also increase with warm temperatures.

Travel and Terrain Advice

  • Daytime warming will weaken surface layers, plan your day around being back to the trailhead early.
  • Minimize exposure to big slopes with cornices, especially during the heat of the day.

Problem 3: Persistent Slabs

Which Elevation?
Which Elevation? alpine
Which Slopes?
Which Slopes? east, south, southwest, southeast, west
Chance of Avalanches?
Chance of Avalanches? unlikely - possible
Expected Size?
Expected Size? small - large

Though not widespread, this layer of facets over crusts from mid April has been reactive in the alpine for a couple weeks and may persist for the next week or two. Some deeper persistent layers may also wake up as temperatures climb later in spring.

Travel and Terrain Advice

  • Dig down to find and test weak layers before committing to a line.
  • Watch for signs of instability such as whumpfing, or cracking.
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

Go to www.avalanche.ca/weather/forecast for the current weather forecast.

Snowpack Discussion

New snow instabilities are generally settling rapidly and alpine N aspects remain cold and dry. Concern remains for alpine solar aspects where April facets between crusts have been reactive in the past week. Treeline and below a spring melt freeze snowpack exists with crusts in the AM and increasing hazard in the PM depending on temperatures.

Avalanche Activity Discussion

As of May 5th, loose wet avalanches with daytime warming on solar aspects and lower elevations, and a few wind and storm slabs in the alpine up to size 2 were reported in the past week. Increasing temperatures in the next weeks will lead to increased avalanche avalanche activity and cornice failures especially during the hottest parts of the day.

For More Details

Emergency: (403) 762-4506
Forecasters: (403) 762-1470

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