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Avalanche Forecast

Archived

Feb 25th, 2021–Feb 26th, 2021

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

Regions

Kootenay Boundary.

New snow and wind have formed reactive storm slabs at all elevations. Conservative terrain choices will be critical to playing safe on Friday.

Expect hazard to be HIGH in portions of the region that receive 20 cm. or more snow Thursday night.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Forecast snowfall amounts are uncertain.

Weather Forecast

  

THURSDAY NIGHT: Snow; 10-20 cm. / Strong, west ridgetop wind / Alpine low -10 / Freezing level valley bottom.

FRIDAY: Cloudy with flurries; 3-5 cm. / Light, northwest ridgetop wind / Alpine high -4 / Freezing level 1200 m.

SATURDAY: Mix of sun and cloud / Light, northwest ridgetop wind / Alpine high -5 / Freezing level 1000 m.

SUNDAY: Mix of sun and cloud / Strong, northwest ridgetop wind / Alpine high -4 / Freezing level 1200 m.

Avalanche Summary

No new avalanches were reported in this region on Wednesday. However, the incoming snow and strong west winds are expected to form storm slabs reactive to human triggers.

Snowpack Summary

20 cm. of new snow and strong southwest winds on Thursday have formed fresh storm slabs that will be reactive to human triggers.

Weak surface hoar sitting on a crust on solar aspects was reported in the Kootenay Pass area prior to the storm. This layer may also be present in other areas within the region. Storm slabs will be more sensitive to human triggering in areas where this weak layer was preserved before being buried; especially if the surface hoar is sitting on a crust.

The main persistent layer of concern below the surface is a combination of surface hoar, facet, and crust layers that formed in January that are now buried 60-150 cm. deep. Steep, open slopes at treeline elevations are the most likely spots to trigger a large avalanche on this layer.

Terrain and Travel

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.