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Avalanche Forecast

Archived

Mar 28th, 2021–Mar 29th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Kootenay Boundary.

Be in initial assessment mode as you check out the outcome of the storm, especially if forecast snowfall is exceeded. Expect to find reactive new wind slabs in exposed terrain but keep your guard up in sheltered areas until you have good info about how the new snow is bonding.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Continuing snowfall bringing 5-10 cm of new snow, easing by morning. Winds becoming strong northwest. Freezing levels returning to valley bottom.

Monday: Cloudy with isolated flurries. Moderate to strong northwest winds. Alpine high temperatures around -12.

Tuesday: Mainly cloudy. Light to moderate west winds. Alpine high temperatures around -3 with freezing levels to 1600 metres.

Wednesday: Sunny. Light to moderate southwest winds. Alpine high temperatures to around 0 as freezing levels climb to 2000 metres, continuing to rise overnight.

Avalanche Summary

A couple of MIN reports from Saturday near Ymir Peak detail a large (size 2.5), potentially remote triggered wind slab on a south aspect at 2300 metres. Check both reports for the story and the images. Heating from solar exposure was suspected to have contributed to triggering the slide. Quite a few more small loose snow avalanches were reported elsewhere in the region.

Looking forward, new snow from Sunday's storm may need a day to settle and bond to the surface in areas where the surface refroze into a crust in advance of the snowfall. Extra caution should be taken in wind loaded areas, which may begin to include more south slopes as a forecast shift to north winds takes place.

Snowpack Summary

Up to 25 cm of new snow may accumulate by the end of Sunday's storm. For the most part, the new snow buries surfaces that became moist with daytime warming on Saturday. There is some uncertainty about the extent to which this moist snow refroze into crust in advance of the storm. The new snow adds to settled dry storm snow on high elevation north aspects.

Below an additional 30-40 cm of snow accumulated through last week and weekend there is a widespread melt-freeze crust, with the exception of high north-facing terrain where faceted snow or surface hoar may exist at this interface.

Terrain and Travel

  • Carefully monitor the bond between the new snow and old surface.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.