Avalanche Bulletin - Jasper National Park - Sun Apr 30, 2017

Issued: Sat Apr 29, 2017 17:00
Valid Until: Sun Apr 30, 2017 17:00

Spring conditions are here and fine skiing can be found at all elevations. Pay close attention to the freezing levels and plan to finish your day before the melt freeze crust breaks down and the afternoon avalanche cycle starts. [AH]

Public Avalanche Forecast
Spring Conditions:  Saturday
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
Marmot Basin 0800 Not Available Not Available Not Available Not Available Not Available Not Available
Columbia Icefields area 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? west, southwest, south, southeast
Chance of Avalanches?
Chance of Avalanches? possible - likely
Expected Size?
Expected Size? small - large

Freezing overnight temperatures decrease this danger in the morning, it increases with daytime heating, sun and rain. Most widespread during the late afternoon on solar facing slopes. Sluffs from rocks can trigger large slides once the snow is wet.

Travel and Terrain Advice

  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.
  • Pay attention to sluffing off cliffs and steep solar terrain, signs of a warming snowpack.

Problem 2: Cornices

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

Cornice failures are more likely with warm alpine temperatures.

Travel and Terrain Advice

  • Avoid travel on slopes that are exposed to cornices overhead.
  • Give cornices a wide berth when travelling on or below ridges.

Problem 3: Deep Persistent Slabs

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

The deep instability is well bridged by a solid mid-pack; however, it could be triggered by a cornice failure. This problem will transition to wet slabs as the snowpack warms this spring.

Travel and Terrain Advice

  • Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
  • Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.
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

Cool, unsettled conditions will dominate through the weekend with isolated convective storms possible on Sunday.  Freezing levels are expected to hover around 1700 m overnight resulting in poor recovery on Sunday morning.

Snowpack Discussion

Winter conditions exist in the high alpine on Northerly slopes with up to 20 cm of loose new snow sitting over a well consolidated upper snowpack. Spring conditions exist on all other aspects and elevations with a melt freeze crust that is dependent on overnight freezing conditions.  The snowpack is moist to wet snow to ground below this crust.. 

Avalanche Activity Discussion

Avalanche activity will increase after warm nights and/or with thermal inputs such as rain, solar radiation and daytime warming. The avalanche danger will be lowest after cold nights and strong crust formation and will increase into the afternoon and evening before sunset. Likely trigger spots are rocks, cliffy terrain and shallow snowpack areas.

For More Details

Emergency: 1 (877) 852-3100
Forecasters: (780) 852-6155

Archives

Facebook @ParksMountainSafety