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Avalanche Forecast

Archived

Mar 7th, 2023–Mar 8th, 2023

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.
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, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Moyie.

The sun packs a punch this time of year, even brief periods of strong solar input could increase the reactivity of wind slabs. Reduce your exposure to avalanche terrain and overhead hazard during sunny periods.

Confidence

Moderate

Avalanche Summary

On Sunday and Monday, several natural wind slab avalanches were observed to size 2.5 on westerly aspects between 1800 and 1400 m. These avalanches may have been triggered by cornice fall or strong easterly winds on Saturday night. A skier accidental, size 1.5, wind slab avalanche was reported on a northeast aspect at 1900 m. Check out this MIN from Saturday showcasing the current wind slab problem.

Last week, several skier triggered persistent slab avalanches, up to size 2.5, were reported in the Norns and Rossland region. Many of these avalanches failed on weak layers from February and January and occurred at treeline. Though activity has tapered off on this layer it could still be reactive to large triggers.

Snowpack Summary

40-60 cm of storm snow has been redistributed by shifting winds into wind slabs on all aspects at treeline and above. This storm snow sits over a wind affected layer at all elevations. On open solar aspects, a melt-freeze crust covers the surface.

A layer of surface hoar can be found on shaded slopes, and a sun crust on sun affected slopes buried 40 to 70 cm deep. Another layer from January is buried up to 50 cm below this.

The lower snowpack includes a layer of weak sugary crystals near the ground. These facets are slowly gaining strength and have not produced recent avalanche activity. We continue to track the layer and watch for any signs that it could wake up and produce very large avalanches.

Weather Summary

Tuesday Night

Clear skies. Southeasterly winds 15-25 km/h. Treeline temperatures, low of -9. Freezing levels drop to valley bottom.

Wednesday

Mainly sunny with a few clouds. Easterly winds 15-25 km/h. Treeline temperatures, high of -6. Freezing levels hover around 1300 m.

Thursday

A mix of sun and cloud. Southeasterly winds 10-25 km/h. Treeline temperatures, high of -7. Freezing levels 1000 m.

Friday

Cloudy and scattered flurries, 4-6 cm accumulation. Southeast winds 25-40 km/h. Treeline temperatures, high of -7. Freezing levels remain at valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.

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.

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.