Avalanche Forecast
Issued: Apr 12th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Loose Wet and Deep Persistent Slabs.
cgarritty,
Avalanche Canada
It's easier to list the avalanche problems you don't need to think about on Thursday than the ones you do! Storm slabs gradually giving way to lingering wind slabs and dangerous persistent layers, wet snow problems where the sun pokes out, all while loaded cornices loom over shallow start zones and basal facets. With a scene this complex, it's OK to err on the side of simpler terrain.
Summary
Confidence
Moderate
Avalanche Summary
A serious avalanche incident occurred in the backcountry just east of Revelstoke on Wednesday. Details are available here.
Otherwise, reports from Monday and Tuesday included many more storm slab and wind slab avalanches, several that were noted for being triggered remotely (from a distance) and a significant number of avalanches attributed to the problematic late-March and early April failure planes discussed in our snowpack summary, now buried under the full depth of recent snowfall. The presence of surface hoar and facets in particular has been noted in some of the more prominent reports of touchy conditions from the past few days.
Saturday and Sunday saw an overall increase in wind slab and storm slab activity as the storm touched down in the region. This MIN gives a good sense of the conditions initially at play.
Looking forward, the need for backcountry travelers to manage a wide range of avalanche concerns that vary by elevation and aspect will continue through Thursday at least. Although the most recent storm interface may bond up relatively quickly, deeper persistent interfaces formed in advance of the storm remain in question, triggerable wind slabs are now perched on many steep features, and wet loose or even wet slab potential will ramp up with daytime warming - especially as recent snow sees its first rays of spring sunshine. Meanwhile, the weak basal snowpack persisting in thin alpine start zones continues to adjust as cornices loom above.
Snowpack Summary
The early week storm brought a final, variable, trace to 30 cm of new snow to the region Tuesday night. In most areas below 2000 m these later accumulations overlie a rain crust that formed mid-storm. At higher elevations it brought dry storm snow accumulations to totals around 30-60 cm.
All this snow overlies either a widespread melt-freeze crust buried April 7, a weak interface of faceted snow and surface hoar buried at the end of March, or some combination of the two. As surface instabilities settle out, both of these interfaces remain in question with numerous recent avalanches attributed to each and with the snowpack still adjusting to the load.
The mid-snowpack is generally strong but the lower snowpack is a different story. The November facets are still prominent at the base of the snowpack. This layer remains a concern in rocky, shallow, or thin to thick snowpack areas at treeline and above.
Weather Summary
Wednesday night
Mainly cloudy with scattered flurries bringing a trace to 5 cm of new snow except around upper Kootenay Lake and Jumbo Pass where 20-30 cm of new snow may accumulate. Light to moderate northwest winds.
Thursday
Mainly sunny. Light west or southwest winds increasing in late afternoon. Treeline high temperatures around -1 with freezing levels to 1400-1600 m.
Friday
Cloudy with isolated flurries bringing a trace to 5 cm of new snow. Light southwest winds. Treeline high temperatures around 0 with freezing levels to around 1700 m.
Saturday
Becoming cloudy. Light to moderate south winds increasing over the day and evening. Treeline high temperatures around 0 with freezing levels to 1800 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
Problems
Storm Slabs
As surface storm slabs settle and bond, wind loaded features on a wide range of aspects will remain a concern. Some recent slabs may even be obscured by low density snow.
Where they haven't been capped over by thick rain crust, persistent interfaces from late March and early April may still become involved in human triggered avalanches through step-down behaviour or simply for being the weakest remaining failure plane in the wake of the storm. Avalanches triggered on these deeper layers could be large and destructive.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Surface snow will destabilize and may avalanche naturally with daytime warming and especially solar exposure.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's depth.
Suspect terrain for human triggering includes steep, shallow, and rocky terrain where the snowpack transitions from thin to thick.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 13th, 2023 4:00PM
