North Rockies Avalanche Forecast
Issued: Mar 24th, 2021 4:00PM
Ease into terrain very cautiously and watch for signs of instability. Loose snow that reacted as sluffs on Wednesday may behave a lot more like a slab on Thursday. This will almost certainly be the case in wind loaded/affected areas.
Wednesday night: Cloudy with diminishing flurries and up to 5 cm of new snow. Light northwest winds.
Thursday: Cloudy with easing flurries and up to 5 cm of new snow, then clearing over the day. Light to moderate northwest winds, increasing over the day and overnight. Alpine high temperatures around -8.
Friday: Cloudy with scattered flurries bringing less than 5 cm of new snow, increasing a bit overnight. Moderate west winds, becoming strong to extreme southwest overnight. Alpine high temperatures around -5.
Saturday: Cloudy with flurries bringing 5-15 cm of new snow. Strong to extreme southwest winds. Alpine high temperatures around -2.
We don't yet have observations from Wednesday's storm, however it was almost certainly a busy day for natural avalanche activity with 20 cm to 50+ cm of new snow rapidly accumulating in the region.
Earlier snow from the weekend storm was reported as being reactive to rider traffic during the weekend, particularly in steep wind-affected terrain. Slab reactivity and destructive potential likely stepped up a notch with Wednesday's storm.
Looking forward, depending on the bond forming between our new snow and the previous surface, we may see the new snow becoming increasingly reactive to triggers as it settles and gains slab properties. Wind loaded areas will be the most concerning, likely now primed for human triggers.
As of Wednesday afternoon our mid-week storm brought a whopping 50+ cm of new snow to the west of the region from Renshaw to Pine Pass, about 30 cm to Kakwa, closer to 20 cm at Core Lodge.
The new snow has formed widespread new storm slab and wind slab problems above those created by 20 to 30 cm of snow over the weekend. Collectively, the new and recent snow overlies a hard melt-freeze crust up to treeline and to mountain tops on sun-exposed slopes. It's uncertain whether current avalanche activity is limited to new snow or if avalanches might be involving total accumulations from both storms. Under current conditions, the difference might not be terribly significant.
Cornices are also very large along ridgelines and always have the possibility of failing naturally or from the weight of a human.
A weak layer of facets buried mid-February may be found around 100 to 120 cm deep, or shallower in the east of the region and in thin snowpack areas. The most likely place to trigger this layer is where the snowpack is shallow in alpine terrain. Large loads, such a cornice falls or multiple sleds on the same slope, often trigger slopes that single rider couldn't trigger on their own.
Terrain and Travel
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
- Avoid exposure to slopes that have cornices overhead.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
50+ cm of new snow is settling into widespread storm slabs in the west of the region, with about half this amount in shallower parts of the eastern slope. Snow that reacted in dry loose sluffs on Wednesday may react as a touchier slab on Thursday and beyond, particularly where wind loading has occurred.
The persistent slab problem is most likely on the eastern slopes of the region (e.g., Kakwa, Tumbler Ridge) and in areas where the snowpack is thin. Steep, rocky slopes with a shallow or thin to thick snowpack in the alpine are the most likely places to trigger buried weak layers. This problem likely won't go away until substantial melt-freeze cycling occurs.
Valid until: Mar 25th, 2021 4:00PM
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