Avalanche Forecast

Issued: Dec 27th, 2017 4:51PM

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

mbender, Avalanche Canada

South Columbia.

There is uncertainty in forecast snowfall amounts Thursday into Friday. The higher end of estimates will be concentrated in the south of the region.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

THURSDAY: Flurries, accumulation 5-10cm / Wind light south / Alpine temperature -10 FRIDAY: Isolated flurries, accumulation 5-10cm / Wind light to moderate southeast / Alpine temperature -10 SATURDAY: Mix of sun and cloud / Wind light west / Alpine temperature -11

Avalanche Summary

A report from just northeast of Nakusp on Monday shows a size 2 persistent slab release on a north aspect at 1800 metres. Another report from Sunday showed a skier-triggered Size 1 persistent slab releasing from a north aspect at 2200 metres.

Snowpack Summary

Last week's storm brought 50-80 cm of new snow to the region. Predominantly northerly winds have since redistributed this storm snow into wind slabs at higher elevations. In sheltered areas cold temperatures have inhibited slab formation. The storm snow lies over a variety of old surfaces, including surface hoar (weak, feather-like crystals), sun crust, and sugary facets. The bond at this old snow interface is of critical importance in areas where the overlying snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development before the storm, such as sheltered areas at and below treeline or sheltered northerly aspects in the alpine. Recent snowpack tests show wide ranging reactivity on this weak layer but suggest that it may be most reactive on northerly aspects.A rain crust that formed in late November is now buried 90-120cm deep. Recent evidence from adjacent regions suggests it may be reactive in steep, variably loaded terrain features in the alpine.

Problems

Wind Slabs

Recent northwest winds shifting to west and southwest have formed windslabs in the lee of terrain features.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A weak layer of surface hoar buried 50-80 cm deep has potential to produce large avalanches where the overlying snow has settled into a cohesive slab.

Watch for signs of slab formation, such as wind effect, whumpfing, or shooting cracks.Buried surface hoar is more likely to be preserved in sheltered openings at and below tree line.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Dec 28th, 2017 2:00PM