What to expect in the northern Rockies backcountry this weekend


BY AVALANCHE CANADA

Light new snow amounts have been accumulating in the wake of strong to extreme northerly winds that were observed in the region a week ago. More recent winds have been lighter and shifted back to a typical southwesterly flow. As a result, you’re likely to find a mix of old and new wind slabs in exposed terrain, with older, more stubborn slabs on south-facing slopes and more recent and potentially reactive slabs on north through east aspects.

Recent cold temperatures have been influencing conditions as well. Powder snow has been well preserved in areas sheltered from the wind and the cold has progressively reduced the cohesion and reactivity of wind slabs in the days after they formed. It’s not all good news, as more deeply buried weak layers in the mid and basal snowpack have also been preserved and potentially weakened by the sustained cold.  These layers are buried anywhere from 70 to 150 cm below the snow surface and may show themselves as feathery surface hoar (a.k.a. hoar frost) or sugary facets sitting on a crust that was formed back in November.

What to Expect on the Weekend

We’re expecting a fairly dramatic change to the cold and wintery pattern we’ve become accustomed to, but first a light snowfall (5-10 cm) should accumulate by Friday morning. In exposed areas, forecast strong winds are likely to redistribute any new snow into potentially touchy new wind slabs.

Moving forward from Friday, we are expecting a gradual increase in temperatures, freezing levels, and sunshine through the weekend and into the middle of next week. This warming pattern is set to reach a peak on Tuesday, with full sun and freezing levels reaching a possible 2500 metres. This will be the first significant warmup of the season and it is expected to negatively impact the stability of the snowpack over the short term.

Here is what to look out for:

  • New snow releasing naturally in loose avalanches on steep sunlit slopes.
  • New wind slabs that remain reactive to human triggering.
  • Possible wet slab avalanches on slopes that see prolonged solar exposure.

Four factors will also make for a steadily increasing likelihood of deep releases and very large avalanches until at least Tuesday:

  • Strong sunshine on southwest slopes
  • Rising air temperatures penetrating deeper into the snowpack, even on shaded aspects
  • An increasing chance for cornice releases to act as large triggers
  • Poor overnight recovery of the cold temperatures that would normally stabilize the snowpack after a warm day.

Travel Advice

  • Watch for newly formed wind slabs on north through east aspects.
  • Be aware that alpine temperatures may exceed temperatures at lower elevations.
  • Avoid exposing yourself to slopes that are exposed direct sunshine.
  • Be aware of an increasing potential for very large avalanches and avoid runout zones.