Avalanche Bulletin - Glacier National Park - Mon Dec 16, 2019

Issued: Sun Dec 15, 2019 08:00
Valid Until: Mon Dec 16, 2019 08:00

Small avalanches will be easy to trigger in steep terrain. This is as good a time as any to be smart about where you put your uptrack... You never know who might be dropping in above you. [JH]

Public Avalanche Forecast
Danger Ratings: Sunday 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 Monday Tuesday
alpine View Alpine Danger Rating Trend 2 - Moderate 3 - Considerable
treeline View Treeline Danger Rating Trend 2 - Moderate 3 - Considerable
below treeline View Below Treeline Danger Rating Trend 1 - Low 2 - Moderate
Confidence: High
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
Fidelity 1905m -6 -10 5 185 Light (1-25 km/h) SW
Rogers Pass 1315m -3 -7 0 112 Light (1-25 km/h) S
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: Storm Slabs

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

Up to 20 cm of new snow since Dec 11th with light to very light southerly wind. Expect touchy pockets of storm slab in wind exposed features.

Travel and Terrain Advice

  • Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

Problem 2: Dry Loose

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

Surface snow will be prone to sluffing.

Travel and Terrain Advice

  • Use caution above cliffs where small avalanches may have severe consequences.
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
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

A "slack flow" will continue to give a mix of sun and cloud through this evening. A series of weak fronts beginning Monday will give unsettled weather through the week.

Sunday: Mix of sun and cloud with isolated flurries. Alpine temps: Low -15 C, High -13 C, light SW ridge wind.

Monday: Cloudy with flurries (up to 5cm). Moderate SW ridge wind.

Snowpack Discussion

Up to 20 cm of new snow now buries the Dec 11 surface hoar layer. This new snow, combined with light southerly wind, is building pockets of soft storm slab in the Alpine. The Nov 23rd surface hoar/crust/facet combo can be found down +/-100cm (SH is most prevalent in sheltered treeline locations) but has become increasingly stubborn in testing.

Avalanche Activity Discussion

No new avalanches reported or observed.

There were several size 2 natural avalanches in the MacDonald gullies Friday, as well as MIN reports of easily triggered sluffs on all aspects and small skier controlled storm slabs in the Alpine on a North aspect.

For More Details

Emergency: 1 (877) 852-3100
Forecasters: (250) 837-7500

Archives

Facebook @ParksMountainSafety