Bulletin d’avalanche

Yukon

Mar 6 – 10, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

Sun
Mon
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
Sans niveau
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Points saillants

Thursday's extreme wind event significantly altered the landscape. Although spotty, hard wind slabs can be found at all elevations. Travel may be challenging, especially in the alpine. Hard wind slabs are difficult to trigger, but once triggered can produce very large avalanches.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1.5–3

    An extreme wind event has changed the look of the mountains. Wind was strong out of the northeast, north, northwest, west and southwest Thursday into early Friday. Stout wind slabs have formed on all aspects. Sunny breaks may entice us to explore, but don’t underestimate how hard some slabs could be. Triggering would be most likely around rocky outcroppings, or anywhere the snowpack goes from thick to thin. While more difficult to trigger, if one of these hard wind slabs is triggered, it could produce a very large & destructive avalanche.  

    Weakened cornices overhang many ridge lines, give them a wide berth as you travel. 

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

The calm before Sunday’s storm.

FRIDAY NIGHT: Light southwest wind, freezing level at valley bottom, no significant precipitation expected.

SATURDAY: Scattered cloud cover, light to moderate southwest wind, freezing level at valley bottom, no significant precipitation.

SUNDAY: Broken cloud cover, strong south/southwest wind, 2 to 6 cm of snow possible during the day, 5 to 10 cm possible Sunday night.

MONDAY: Broken cloud cover, moderate to strong southwest wind, freezing level at valley bottom, 5 to 10 cm of snow possible.

Avalanche Summary

We received reports of natural avalanches reaching the Klondike highway during the wind event and start zones were reloading Thursday. Our field team got out to survey the damage from the wind event Friday, their detailed observations can be found here.

Snowpack Summary

The extreme wind event delivered wind from a variety of directions, but the main push was done by north (outflow) wind. This event has resulted in new wind slab formation in open terrain at all elevations. The distribution, size and depth of slabs from this event is highly variable. There may be wind loaded snow in areas we traditionally think of as sheltered.

At White Pass the snowpack is roughly 200 cm thick with a strong mid and lower snowpack. Thin snowpack areas further inland may have a shallower snowpack composed of sugary faceted grains. Lower elevations have a melt freeze crust near the surface.

Terrain and Travel

  • Watch for areas of hard wind slab on alpine features.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.

Régions couvertes