Avalanche Forecast
Issued: Feb 12th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.
cgarritty,
Avalanche Canada
Steady snowfall through Monday will continue to form fresh and reactive storm slabs primed for human triggering. This widespread problem will overlap an emerging persistent slab issue recently observed near McBride. Keep in mind that triggering a slab on the surface is probably the most effective way to cause a large and destructive step down avalanche.
Summary
Confidence
Avalanche Summary
A revealing MIN post from the McBride area on Saturday showed concerning evidence of an emerging persistent slab problem associated with what is likely our initial storm interface from early February. Aside from easy test results in surface layers, a more problematic layer of surface hoar buried 65 cm deep in this below treeline area appears to be the culprit in numerous touchy persistent slab releases. This activity suggests extra caution is currently needed to manage overlapping storm slab and persistent slab problems.
Snowpack Summary
Another 15-30 cm of new snow is expected to accumulate over higher terrain in the region by end of day Monday, adding to an impressive 80-120 cm of storm snow accumulated over the past week. The latest of this new snow came with strong to extreme southwest winds.
The bond of this recent snow to recent storm interfaces has come into question with a recent observation from the McBride area that suggests a number of active failure planes within and at the base of this storm snow, all of which have given easy to moderate and sudden snowpack test results and very concerning remote triggering below treeline.
Two layers of surface hoar crystals and/or melt-freeze crust sit in the mid-snowpack. The roughly 1 m deep surface hoar is most likely found around shaded treeline and lower alpine elevations. (It may in fact be the 65 cm-deep layer described in the linked MIN post.) The roughly 150 cm-deep melt-freeze crust is found up to 1800 m on all aspects and into the alpine on sun-exposed slopes. These layers continue to be tracked by local operators, but only the surface hoar layer seems like it might currently be an active weak layer.
A final concerning weak layer in the snowpack is composed of large and weak facets from November located near the base of the snowpack. Although this layer hasn't produced avalanches recently, it continues to guide terrain selection by professionals in the region.
Weather Summary
Sunday night
Cloudy with continuing snowfall bringing 10-15 cm of new snow. Strong southwest winds easing in the morning.
Monday
Cloudy with lingering flurries bringing 5-10 cm of new snow. Light to moderate west winds, easing over the day. Treeline high temperatures around -7.
Tuesday
A mix of sun and cloud. Light northwest winds shifting southwest. Treeline high temperatures around -10.
Wednesday
Mainly cloudy. Light to moderate southwest winds. Treeline high temperatures around -8.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Use careful route-finding and stick to moderate slope angles with low consequences.
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Storm Slabs
Continuing, convective snowfall and strong southwesterly winds are building storm slabs and wind slabs that will be reactive to natural and human triggers. Expect wind loaded spots to be particularly touchy.
Keep in mind that storm slabs have the potential to step down to deeper weak layers, resulting in large and consequential avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A surface hoar layer found in the upper 100 cm of the snowpack has recently been touchy to human triggering and may be most problematic in open terrain below treeline. Be especially cautious around steep openings at low and mid elevations, especially where recent storm snow has been wind loaded.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
A layer of large and weak facets sits near the base of the snowpack. This layer is most prominent in upper treeline and alpine elevations. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain. Your best defence is to stay diligent in choosing low-consequence terrain away from overhead exposure.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 13th, 2023 4:00PM
