Avalanche forecast

South Rockies

Mar 19 – 20, 2019Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

Another day of sun and warm temperatures will maintain very dangerous avalanche conditions on Wednesday. Travel in avalanche terrain is not recommended.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2.5
    Sunshine and warm temperatures will peel away layers or recent snow on sunny slopes as loose wet slides, and weaken cornices. Large loose wet avalanches can threaten lower elevation runout zones with very destructive debris flows.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3
    The weak layers present in our snowpack are undergoing a stress test that increases with each day of warm temperatures and weak overnight cooling. Deep weaknesses in the basal snowpack are especially concerning in thin snowpack areas in the alpine.

Confidence

Moderate -

Weather Forecast

Tuesday night: Clear. Light west winds. Freezing levels rising to 3300 metres.Wednesday: Sunny. Light west winds. Alpine high temperatures around +9 with freezing levels to 3400 metres, dropping slightly overnight.Thursday: Sunny. Light southeast winds. Alpine high temperatures around +8 with freezing levels of 3200 metres, remaining steady overnight.Friday: Sunny. Light variable winds. Alpine high temperatures around +7 with freezing levels around 3000 metres, dropping overnight to 2300 metres by mid-morning Saturday.

Avalanche Summary

A report from Tuesday in the Elk Valley described numerous natural persistent slab releases reaching size 2 (large) on southeast aspects at around 2200 metres. Further to this activity, any sun-exposed snow became isothermal (slushy and lacking cohesion), and huge whumpfs that collapsed the basal snowpack were triggered during ski touring.A report from Sunday in the Window Mountain area described snowshoeing party choosing to turn back after avoiding a large loose wet avalanche that ran into below treeline terrain. This highlights the importance of considering overhead hazards being warmed by the sun and potentially inverted (warmer at higher elevations) temperatures.Given the above activity, loose wet avalanches remain a daily concern in steep, sun-exposed terrain (and in runout zones) while concern is increasing for deep basal snowpack weaknesses that have the potential to produce very large and destructive slab avalanches.

Snowpack Summary

Upper snowpack: Getting warm and moist during the day, likely forming weak crusts overnight that deteriorate during the day. On sunny aspects there may be buried crusts serving as sliding layers. On lee slopes there may be buried hard layers of wind effected snow (buried wind slabs).Mid pack: The mid-snowpack consists of sugary faceted grains (facets) and layers of harder wind effected snow. In isolated sheltered locations a thin surface hoar layer from mid-January is 50-80 cm deep. The surface hoar is most prominent in the Elk Valley between 1600 - 1900 m. Lower pack: The strength of the lower snowpack is increasingly in question in shallower areas where the February cold was able to penetrate and weaken basal layers. Warm temperatures are increasing the strain on basal weaknesses each day.Forecasting how many sunny days and warm nights it's going to take to wake up deeper layers is tough, but we can say with confidence that it's a good time to stand aside and let the mountains shed their coat. Stability will improve greatly when temperatures cool off.

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