Archived

Avalanche Forecast

Dec 31st, 2017–Jan 1st, 2018

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Purcells.

A stable weather pattern to start the new year and possible temperature inversion mid-week. Consider the potential to trigger persistent slabs as the recent storm snow starts to finally settle and consolidate more rapidly.

Confidence

Moderate - Freezing levels are uncertain on Wednesday

Weather Forecast

MONDAY: Mix of sun and cloud / Light to moderate northwest wind / Alpine temperature -10 TUESDAY: Mix of sun and cloud / Light west wind / Alpine temperature -5, possible temperature inversion WEDNESDAY: Cloudy with sunny breaks / Light to moderate west wind / Alpine temperature -1, temperature inversion

Avalanche Summary

On Saturday a skier triggered size 2 persistent slab avalanche running on a layer of facetted snow from Mid December was reported. This happened in the north of the region's Dogtooth Range on a west aspect at 2400m. On Sunday there was also a report of a skier triggered avalanche near Mount Goldie just south of Invermere. There are no details on this avalanche at this time. Recent reports continue to show both natural and human triggered loose dry avalanches in steep terrain to size 1 and 1.5 in areas that have not been affected by wind. Additionally storm slab avalanches have been reported in the alpine to size 1.5. Expect continued potential for triggering loose dry avalanches in steep terrain and consider the potential to trigger persistent slabs where last week's storm snow has settled into a cohesive slab.

Snowpack Summary

20-40 cm low density new snow has accumulated and buried a recently formed layer of weak feathery surface hoar and/or sugary facets. Another layer buried mid-December that consists of surface hoar, sun crust and/or sugary facets is down approximately 40-70cm. The bond at this old snow interface is of critical importance where the overlying storm snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development prior to mid-December, such as sheltered areas at and below treeline and any area where the surface hoar may have formed on top of a sun crust. Recent snowpack tests show wide ranging reactivity on this layer but suggest that it may be most reactive on northerly aspects. A rain crust that formed in late November is now buried 70-110cm deep. Recent reports show this layer to be unreactive at this time.

Avalanche Problems

Wind Slabs

20 to 40cm of low density new snow has accumulated in the region the past 3 days. Where accumulations are higher expect the new snow to sluff and gather mass in steep terrain. West, northwest and southeast winds have created windslabs in alpine lees.

Be cautious as you transition into wind affected terrain.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Persistent Slabs

A weak layer of surface hoar buried 30-50 cm deep may be reactive where the overlying snow has settled into a cohesive slab.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Approach steep open slopes cautiously at and below treeline where buried surface hoar may exist.Sluffs may trigger deeper instabilities.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 1 - 3