Avalanche Forecast

Issued: Dec 18th, 2018 4:35PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Persistent Slabs and Storm Slabs.

mbender, Avalanche Canada

Kootenay Boundary.

The load continues to grow on a weak layer buried in early December. As a result this persistent slab is primed for human triggering and a conservative approach is recommended.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

TUESDAY NIGHT: Flurries, accumulation 5-10 cm. Alpine temperature -2. Moderate to strong southwest wind. Freezing level 1400 m.WEDNESDAY: Isolated flurries. Alpine temperature -4. Light west wind. Freezing level 1200 mTHURSDAY: Snow, accumulation 15-25cm. Alpine temperature -1. Moderate to strong southwest wind. Freezing level 1500 m.FRIDAY: Cloudy with sunny breaks. Alpine temperature -7. Light west wind. Freezing level at the valley bottom.

Avalanche Summary

Recent reports indicate explosives controlled and natural storm slab avalanches running to size 2 on Monday on a variety aspects at tree line and in the alpine.

Snowpack Summary

The primary concern in the snowpack is the layer below last week's storm snow accumulations; that would be the Dec 09 (date it was buried) layer of facets (sugary crystals), surface hoar (feathery crystals) and a sun crust on south aspects all about 60 cm deep. After the latest storm Monday night into Tuesday, the Dec 09 will be 70-80 cm below the surface, as well as some new storm & wind slab issues (say within 30 cm of the surface, deeper in wind loaded pockets). Although 10 or 15 cm of new snow daily often won't start a natural avalanche cycle, it looks like we're getting real close to tipping the balance. The Dec 09 layer, it's primed; recent "sudden" snowpack test results and remotely triggered avalanches indicate it remains a critical layer. If the forecast storms materialize I expect this layer may wake up as we continue to build the load on top of it.Lower in the snowpack, previous weak layers from November appear inactive. These deeper layers could possibly cause problems on cold (north facing) slopes at high elevations where the snowpack is thin, but in most places, this is unlikely.

Problems

Persistent Slabs

A weak layer buried around 70 cm is the primary concern. This concern is heightened on steep slopes where wind has drifted snow into a reactive slab.

Choose low angle and supported terrain and watch for clues of instability.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 3

Storm Slabs

Recent new snow and strong winds have set up wind slabs in exposed areas, particularly on north to east aspects. With more than 20 cm of new snow in the past 24 hours, steeper slopes and rolls on all aspects are also suspect!

Use caution in lee areas. Recent wind loading have created wind slabs.Stick to simple terrain and be aware of what is above you at all times.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Dec 19th, 2018 2:00PM