Avalanche Forecast

It's been a very busy time for large, destructive avalanches in the region.

Deep persistent slabs figured prominently in reports from the region again on Thursday, with explosives yielding avalanches from size 2 (large) to size 3.5. Size 3.5 is a VERY large avalanche. This was going on above 2500 m in central part of the region between the Bugaboos and Dogtooth. Up in the Esplanade, a skier-triggered size 1 running on a 40 cm-deep surface hoar layer was reported as well. This occurred after a ski cut had been attempted on the slope.

On Tuesday and Wednesday, operators across the region used explosives on a wide range of slopes (aspect and elevations). Explosives produced several smaller storm slab and wind slab avalanches, but more importantly numerous size 2.5- 3 deep persistent slabs that released at the base of the snowpack.

On Monday, A few small (size 1 to 1.5) human-triggered slabs were reported, mostly failing on a 30 cm deep surface hoar layer. A few larger (size 2) human-triggered slabs were reported in the Esplanade range. Explosive avalanche control produced multiple large (size 2) and one very large (size 3) deep persistent slab.

All of these recent occurrences tell us that large loads have strong potential to initiate deep avalanches and that human triggering is a serious concern, particularly in thin or variable depth spots (rocks, thin to-thick areas) of the snowpack.

15-25 cm of recent storm snow can be found in sheltered areas, while open terrain has been wind affected. The recent snow overlies a mid-January interface that includes small surface hoar all the way into the alpine in some parts of the region as well as a rain crust that can be found up to 2000 m in most parts of the region.

There are two additional concerning weak layers in the top metre of the snowpack. The first is a layer of surface hoar from early January - down 30-50 cm. The second is a layer of surface hoar, facets, and a crust from December, down 40-90. The surface hoar is most prevalent in sheltered areas while crusts and any associated faceted snow have more uniform distribution.

The bottom of the snowpack contains yet more weak, faceted snow that continues to produce large avalanches and will likely persist for a prolonged period of time.

All of these interfaces are at their shallowest in the east of the region and all of them have produced avalanches recently.

In general, even in the west of the region, the snowpack is shallow and weak.

Friday night

Mainly clear. Light southwest or northwest winds, more northerly with elevation.

Saturday

A mix of sun and cloud. Light southwest winds, moderate in the alpine. Treeline high temperatures around -3.

Mainly sunny. Light to moderate northwest winds. Treeline high temperatures around -6.

Mainly cloudy with isolated flurries in the afternoon/evening. Light west winds. Treeline high temperatures around -9.

More details can be found in the Mountain Weather Forecast.

• Be mindful that deep instabilities are still present and have produced recent large avalanches.
• Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.