Lawinenlagebericht

South Rockies

Mar 13 – 14, 2021Avalanche Canada
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Archiviert · abgelaufen 6 years ago

Lawinengefahr

Mon
Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

It's going to be a hot and sunny day! Temperatures are forecast to stay above freezing between 1500 m and 2500 m overnight. On Saturday, solar input and the freezing level rising to 2800 m will weaken cornices and may increase the reactivity of the persistent weak layers. 

Lawinenprobleme

  • Cornices

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely - Very Likely
    Größe
    1.5–2.5

    Temperatures are forecast to stay above freezing between 1500 m and 2500 m overnight which will weaken cornices and the snowpack during the night. Cornices will become especially weak with daytime heating and the freezing level rising even higher to 2800 m during the day. Large cornice falls are a hazard of their own and can also trigger large persistent slab avalanches on the slopes below. 

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    Two persistent weak layers exist in the snowpack that could be triggered by riders:

    • The upper layer is buried 30 to 60 cm and primarily consists of weak faceted grains.
    • The deeper layer is buried 60 to 100 cm and consists of surface hoar, faceted grains, and/or a hard crust.

    The most likely areas to trigger these layers is where a hard wind slab exists above the layers and where the snowpack is not capped by a thick melt-freeze crust. Warm temperatures and solar input may increase the reactivity of these two layers. 

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Solar input and warm temperatures may weaken the upper snowpack and form wet loose avalanches. These avalanches will most likely occur on steep solar slopes and around rock outcrops. The likelihood for wet loose avalanches will increase with daytime heating. Pinwheeling and a moist snow surface are signs that the stability of the upper snowpack is decreasing. 

    Even small avalanches can be a hazard in high consequence terrain and above terrain traps. 

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

FRIDAY NIGHT: Mostly clear, 15 km/h northwest wind, alpine low -9 C, above freezing layer between 1500 m and 2500 m.

SATURDAY: Sunny, 10 km/h south wind, alpine high +7 C, freezing level 2800 m.

SUNDAY: Sunny, 15 km/h south wind, alpine high +7 C, freezing level 2700 m.

MONDAY: Mix of sun and cloud, trace of new snow, 20 km/h northeast wind, alpine high +4 C, freezing level 2100 m.

Avalanche Summary

No new avalanches were reported for the area on Friday.

Snowpack Summary

A dusting of snow overlies a thick melt-freeze crust in many areas, with the exception being on north aspects above around 1700 m. Old wind slabs may exist on northerly aspects at alpine and treeline elevations, whereas windward slopes have been scoured to rocks or a hard crust. On solar aspects and below the freezing level, the snow may moisten during the heat of the day. Cornices may also weaken over the day.

Around 30 to 60 cm of snow sits above a persistent weak layer of sugary faceted grains that was buried in mid-February. There have been a handful of avalanches that released on this layer in the past few weeks. There is another persistent weak layer that was buried at the end of January, found around 50 to 80 cm deep. This layer consists of feathery surface hoar, facets, and/or a hard melt-freeze crust. Periodic avalanches continue to be triggered on these layers by riders, particularly where a stiff wind slab sits above them. Check out this MIN that shows the positioning of the layers in the snowpack near Crowsnest Pass.

Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack. 

Terrain and Travel

  • Cornices become weak with daytime heating or solar exposure.
  • Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Be alert to conditions that change throughout the day.

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