Avalanche Bulletin - Banff, Yoho, and Kootenay National Parks - Tue Jun 27, 2017

Issued: Mon May 15, 2017 17:00
Valid Until: further notice

This is the last scheduled avalanche bulletin for the season. Above average snowpack at high elevations means we should have an extended spring ski season! Check out the Mountain Conditions Report weekly regional summaries for up to date conditions. [IJ]

Public Avalanche Forecast
Spring Conditions:  Monday
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.

More Spring Conditions details.

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: Loose Wet

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

Loose wet avalanches are occurring on all aspects and elevations during the warmest parts of the day, especially when the sun comes out. Some of these are also triggering wet slabs. Plan your trip to be out of any big terrain before things heat up!

Travel and Terrain Advice

  • Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

Problem 2: Wet Slabs

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

Wet slab avalanche activity will taper off with cooling and increase during hot periods of the day, with large triggers like cornices or when there is no overnight refreeze. The deep facets will remain a problem through the spring season.

Travel and Terrain Advice

  • Travel early before the heat of the day melts surface crusts, and avoid big slopes in the afternoon.

Problem 3: Cornices

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

Cornices have taken quite a hit with the recent heat. Many are cracked and slowly peeling off of ridges. These should be considered suspect as they will likely fail in the coming weeks.

Travel and Terrain Advice

  • Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.
  • Cornices become weak with daytime heating, so travel early on exposed slopes.
Problem Glossary
Loose Dry
  • 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.
Loose dry 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.
Loose Wet
  • Are more powerful than loose dry avalanches due to their higher density.
  • Are often limited to sunny slope aspects.
  • Are commonly confined to the warmest part of the day.
Loose wet 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

Some helpful weather links:

Remote weather stations in Banff, Yoho & Kootenay - Real time, raw, actual weather data.

Avalanche Canada Mountain Weather Forecast - Good for getting an overview of the major weather systems.

SpotWx - Good for a localized forecast

Environment Canada Yoho forecast - Simplified valley bottom forecast for Lake Louise area.

Snowpack Discussion

Isothermal snow exists at lower elevations. Crusts formed during clear cool nights will break down quickly with solar inputs. Expect moist surface snow to mountain top in the afternoon with the exception of high elevation North slopes. The basal facet weakness persists at treeline and above and is reactive to large triggers or warm temperatures.

Avalanche Activity Discussion

In general, avalanche hazard will be greatest during hot sunny days or warm rain. This has the potential to trigger smaller loose wet avalanches and larger wet slab avalanches on the basal weak layer. For current avalanche activity and observations, check out the Mountain Conditions Report

For More Details

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

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