Boletín de aludes

North Rockies

Feb 28 – Mar 3, 2020Avalanche Canada
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Archivado · caducó 7 years ago

Peligro de aludes

Sun
Mon
Alta montaña
4 · Fuerte
Límite del bosque
4 · Fuerte
Bajo el límite
3 · Notable
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Lo esencial

For all the region except the north, a strong storm on Friday night will build slabs that will likely be reactive this weekend, requiring terrain avoidance and a conservative mindset to travel safely. For the north, treat the danger as CONSIDERABLE with less snow but windy.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely - Possible
    Tamaño
    2–3

    A buried surface hoar layer may still exist around Pine Pass, and potentially other parts of the region too. It may be found around 50 to 100 cm deep, but deeper on wind-loaded slopes. Treeline slopes are most likely to harbour this problem, as seen by photos of avalanches reported on the Mountain Information Network here and here. This layer has been dormant as of late, but could reactive from snow loading with a bit of new snow and strong wind.

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely - Very Likely
    Tamaño
    1–2.5

    For everywhere except the north of the region, around 20 to 30 cm of new snow Friday night to Saturday afternoon will accumulate, with associated south switching to northeast wind. Storm and wind slabs will form quickly and on all aspects, as the wind will shift from south to northeast. Local snowfall amounts could be even higher, particularly on the eastern slopes where local snowfall enhancements could occur. Natural avalanche activity will be likely to occur during and shortly after the storm. These slabs will likely remain reactive to human traffic on Sunday and Monday.

    For the northern part of the region (e.g., Pine Pass), only 5 to 10 cm of snow is forecast to accumulate. However, wind will be elevated and shifting directions, so wind slabs may be found on all aspects in wind-affected terrain and they may remain touchy.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 15 to 25 cm for most of the region and 5 cm in the north around Pine Pass, moderate south switching to northeast wind, alpine temperature -8 C.

SATURDAY: Cloudy with snowfall and afternoon clearing, accumulation 5 to 10 cm for most of the region and trace around Pine Pass, moderate northeast wind, alpine temperature -10 C.

SUNDAY: Mix of sun and cloud, moderate increase to strong southwest wind, alpine temperature -10 C.

MONDAY: Cloudy with snowfall and afternoon clearing, accumulation 5 to 15 cm, strong decreasing to moderate northwest wind, alpine temperature -8 C, freezing level rising to 1000 m.

Avalanche Summary

Within the past few days a few small (size 1) to large (size 2 to 3) wind and storm slab avalanches were reported in the area. They generally occurred within the upper 20 to 50 cm of snow, on north to east aspects, and at treeline and alpine elevations. Some of them may have slid on the melt-freeze crust described in the Snowpack Summary. A few loose avalanches were also noted and they were generally small.

Avalanche activity is expected to increase this weekend due to the stormy conditions that will bring more snow and wind to the region.

Snowpack Summary

A storm on Friday night for most of the region (except around Pine Pass and north) will drop around 20 to 30 cm of snow by Saturday afternoon. This will overly previously wind-affected snow in exposed terrain and otherwise around 20 to 50 cm of soft snow in sheltered terrain. The new snow will fall with south switching to northeast wind, so slabs are expected to be found on all aspects and at all elevations. There are also a couple buried melt-freeze crusts in the snowpack and all this snow may not be bonding well to them. Cornices have been reported as growing large and fragile.

The lower snowpack is strong in many parts of the region with two main exceptions:

  • A weak layer of surface hoar buried 50 to 100 cm has been a problem around treeline elevations at Pine Pass. The layer has also been observed in other parts of the region, such as Torpy, but seems to be less of a problem further south towards McBride. Although unlikely to trigger, an avalanche on this layer would be large.
  • Steep slopes where the snowpack is shallow and rocky could harbour weak basal facets.

Terrain and Travel

  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Make conservative terrain choices and avoid overhead hazard.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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