Avalanche Forecast

Issued: Feb 25th, 2019 4:13PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Persistent Slabs and Wind Slabs.

cgarritty, Avalanche Canada

Kootenay Boundary.

Strong outflow winds have generated reports of wind slab formation on all aspects and elevations. Meanwhile, our lingering persistent slab problem continues to produce large, human triggered avalanches.

Summary

Confidence

High -

Weather Forecast

Monday night: Cloudy with clear periods. Strong northeast winds. Tuesday: Mainly sunny. Moderate to strong northeast winds. Alpine high temperatures around -14.Wednesday: Cloudy with sunny periods. Light east winds. Aline high temperatures around -8.Thursday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Light variable winds. Alpine high temperatures around -8.

Avalanche Summary

Another large (size 2.5) persistent slab was triggered by a skier in the Evening Ridge area on Sunday. It occurred on a southeast aspect at about 2000 metres and featured a crown fracture around 50 cm deep and 350 metres wide. A weak layer from early February is suspected as the failure plane.On Saturday, a few small (size 1-1.5) human triggered slab and loose dry avalanches were reported. One large (size 2.5) naturally triggered persistent slab avalanche was observed on a south aspect near Paulson Summit.Human triggered avalanches were reported everyday between February 12 and 20. Although most avalanches were small (size 1-1.5), some had impressive propagation on buried weak layers (see some examples here and here). Last Tuesday, a notable size 3 persistent slab avalanche occurred on an east aspect at 2000 m. This avalanche was triggered by explosives and failed on the persistent weak layer that was buried on February 7th.

Snowpack Summary

The latest storm brought 15-25 cm of low density snow that now covers variable wind slabs at higher elevations and sun crusts on south-facing slopes. Fresh wind slabs have formed in exposed terrain under the influence of increasing northerly winds.A weak layer of surface hoar (feathery crystals) and a crust that was buried on February 7th is now 30-50 cm deep. This layer has been reactive, and has produced avalanches as large as size 3. Two other surface hoar layers are buried 50 to 80 cm deep the snowpack (referred to as the February 1st and mid-January layers). Although they have not been reactive recently, they are still being monitored by professionals. The lower snowpack is considered generally strong.

Problems

Persistent Slabs

It remains possible to trigger an avalanche on one of the surface hoar or crust layers buried 30 to 80 cm deep. These layers are most prominent around treeline elevations.

Caution around sheltered open areas at treeline and below including cutblocks, gulleys, and glades.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Use increased caution on open slopes and convex rolls at lower elevations.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Wind Slabs

Northeast winds have formed fresh slabs in exposed terrain at all elevations. Old wind slabs also linger on a variety of aspects.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Feb 26th, 2019 2:00PM