Avalanche Forecast

Archived

Apr 12th, 2023–Apr 13th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

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.

Regions

West Purcell, Badshot-Battle, Goat, Retallack.

More new snow = touchy new avalanche problems. A localized storm over Wednesday night is expected to keep avalanche conditions in the region especially lively through Thursday. Expect any sustained solar exposure to quickly initiate natural avalanche activity.

Confidence

Moderate

Avalanche Summary

A serious avalanche incident occurred in the backcountry just east of Revelstoke on Wednesday. Details are expected to be posted on the MIN shortly.

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.

At least one deeper persistent slab was observed with a 100 cm crown fracture in the western Purcells.

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, further loading of new snow through Wednesday night will maintain active avalanche conditions for Thursday, with new storm and wind slabs likely, slightly deeper persistent interfaces still in question, and wet loose or even wet slab potential ramping up with daytime warming.

Snowpack Summary

This region is expected to receive a localized storm late in the day/evening Wednesday with accumulations of 20-30 cm.

A later pulse of the early week storm brought a variable trace to 30 cm of new snow to the region Tuesday night. In most areas below 2000 m these recent accumulations overlie a rain crust that formed mid-storm. At higher elevations it brought dry storm snow accumulations to totals around 30-60 cm (and counting).

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 a localized storm bringing 20-30 cm of new snow. 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

Use increased caution at all elevations. Storm snow is forming touchy slabs.
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.
Minimize exposure to sun-exposed slopes when the solar radiation is strong.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.