Avalanche Forecast

Archived

Feb 11th, 2023–Feb 12th, 2023

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 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.

Regions

Lizard-Flathead, South Rockies, Flathead, Lizard, Bull, Elkford East, Elkford West.

The impact of recent wind was extensive and left unstable wind slabs in alpine and treeline terrain.

Confidence

Moderate

Avalanche Summary

Several skier-triggered wind slab avalanches were reported in the Fernie area on Friday. They were size 1 to 2, occurring in both alpine and open forested terrain, as illustrated in MIN reports here, here, and here. Earlier in the week, there were several natural and explosive triggered storm and wind slab avalanches.

Wind slab avalanches will continue to be possible to trigger at upper elevations throughout the region and deep persistent slab avalanches should be on your radar in the Elkford and Flathead areas.

Snowpack Summary

Wind-affected snow is fairly extensive, with wind slabs reported into sparsely forested terrain at treeline. 10 to 30 cm of soft snow from earlier this week can be found in wind-sheltered terrain. The snow overlies old wind slabs, or a melt-freeze crust below 1900 m.

In the Lizard range specifically, the mid-pack is consolidated with a supportive 10 to 20 cm thick frozen crust buried 80 to 100 cm.

In the Elkford and Flathead areas, deeply buried weak layers are slowly gaining strength but are still a concern, especially in steep rocky terrain features where the snowpack is thin.

Weather Summary

Saturday night

Partly cloudy, no precipitation, 30 to 40 km/h west wind, treeline temperatures drop to -8 ºC.

Sunday

Sunny periods in the morning then increasing cloud in the afternoon, no precipitation, 40 to 50 km/h southwest wind, treeline temperatures to -4 °C with freezing level climbing to 1500 m.

Monday

Flurries with 10 to 15 cm of new snow, 50 to 70 km/h southwest wind, treeline temperatures to -4 °C with freezing level climbing to 1500 m.

Tuesday

Mix of sun and cloud, no significant precipitation, 20 km/h north wind, treeline temperatures drop to -10 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Be especially cautious as you transition into wind affected terrain.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.