Bulletin d’avalanche

Vancouver Island

Feb 2 – 3, 2021VIAC
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Archivé · expiré 6 years ago

Danger d’avalanche

Wed
Thu
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Points saillants

We are releasing a SPECIAL PUBLIC AVALANCHE WARNING for Vancouver Island in conjunction with Avalanche Canada. We received multiple reports of human triggered avalanches (Size 2+) from mid island to North island including two separate incidents with full burials and serious injuries. These two separate and serious avalanche incidents occurred at the Below Treeline and Treeline Elevation Bands. The likelihood of people triggering an avalanche on a slope steeper than 30 degrees is "very likely" and/or "certain" at this time. Please ski and snowmobile safely, select low angle terrain (terrain under 30 degrees) until the new snow load consolidates and general snowpack stability improves. Avalanche Forecaster confidence is HIGH : Based on extensive data collection all week as well as many people submitting observations from the field.

Problèmes avalancheux

  • Wind Slabs

    • Toutes altitudes
    Probabilité
    Possible
    Taille
    1
    Forecasted winds should create Wind slabs that can be found in down wind terrain. This wind slab overlies either a thick crust or a surface hoar layer, making it unstable. Wind slab problems may become increasingly likely (avalanche prone) later in the week on Thursday with the arrival of Extreme wind speeds at mountain top and light low density snow available for transport. Location: Northeast to Northwest alpine and treeline features. Possibility: Triggering of this avalanche problem is “likely to very likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” to “likely” depending on the elevation band. Size: If triggered, expect these avalanches to be large enough to bury a person, size 2.

  • Storm Slabs

    • Toutes altitudes
    Probabilité
    Possible
    Taille
    1
    New storm slabs will form and be present on terrain that is not exposed to the wind. Wet slabs are expected during periods of rain. Expect the slab sensitivity to triggering and propagation to increase as temperatures increase. Location: Widespread on aspects and at all elevation bands. Possibility: Triggering of this avalanche problem is “Very Likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” depending on the elevation band. Size: If triggered, expect storm slab avalanches on specific terrain features to be size 1 and up to size two on isolated features.

  • Wet Slabs

    • Toutes altitudes
    Probabilité
    Possible
    Taille
    1
    Above zero degrees air temperature and precipitation in the form of rain will rapidly decrease the stability and add additional load to the already tenuous persistent weak layer problem. Location: Widespread All aspects and at below treeline elevation band. Possibility: Triggering of this avalanche problem is “possible” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “unlikely.” Size: If triggered, expect these avalanches to be small but will entrain and could become large up to size 2 with enough mass to bury, injure or kill a mountain traveller.

  • Deep Persistent Slabs

    • Toutes altitudes
    Probabilité
    Possible
    Taille
    1
    There exists major reactivity on the persistent slab interface due to new storm snow load. We are very concerned about our two persistent weak layers (PWL), forming our deep persistent slab problem. This layer is reactive to ski and snowmobile triggers and has triggered multiple large avalanches (and full burials of people) over the past several days. Location: Found at all elevation bands and on multiple aspects. Possibility: Triggering of this avalanche problem is “likely to very likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” to “likely” depending on the elevation band. Size: If triggered, expect these avalanches to be large enough to bury a person (size 2-3).

Weather Forecast

The weather pattern for Vancouver island will be quite dynamic for the next several days. Unfortunately, incoming weather is such that the current snowpack instabilities will not see an improvement to stability in the short term.Tuesday (10 cm Snow to 25 cm Snow), Moderate Southerly winds gusting to strong Southerly winds in the afternoon, Freezing level 850MWednesday: (5 cm Snow to 10cm Snow ), Moderate winds from the North, Freezing level 950MThursday (Less than 10cm Snow for North Island) and (5mm Rain for Below Treeline and Treeline Elevation band for South and mid-island), Extreme winds from the Southwest, Freezing level begins at 700M elevation in morning and rises to 1700M elevation late afternoon.

Terrain Advice

Keep to simple terrain (terrain under 30 degrees slope angle) and utilize small slopes to test the reactivity of the recent snowfall.Keep an eye on snowfall rates, wind transport and rising temperatures for your area, as this promotes slab formation and “touchy/easily triggered” conditions.Be cautious when route-finding and transitioning from scoured areas into areas of wind loaded snow.Avoid open and steep slopes during periods of warming and rain. A small loose wet avalanche will entrain and gain enough mass to push a mountain traveller into gullies and over cliffs.Tree well hazards will pose a major hazard this weekend if the forecasted precipitation/winds arrive as predicted. Keep an eye on your riding group and ride in pairs.Avoid travelling above or below cornices and keep to conservative decision-making.

Snowpack Summary

Over the weekend, 40 cm to 70cm of snow fell and was transported by southeast winds creating slabs in the current affected areas. This overlies a sandwich of reactive melt-freeze crusts and persistent weak layers (PWL's) within the upper 60-80 cm of the upper snowpack. Below this, the snowpack is well settled.

Snowpack Details

  • Surface: 40cm to 70cm of new snow
  • Upper: Two persistent weak layers (contributing to dangerous avalanche conditions on Vancouver Island)
  • Mid: Well settled and dense.
  • Lower: Well settled and dense.

Confidence

High -

Past Weather

Cold temperatures (below zero degrees) and strong to moderate precipitation have left the mountain environment on Vancouver Island with 40cm to 70+cm of new snow. Warmer air temperatures Monday Feb 1st have brought additional snow and possibly rain to the Below Treeline elevation band.

Régions couvertes