Avalanche Forecast

Issued: Jan 31st, 2016 7:30AM

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.

rbuhler, Avalanche Canada

South Columbia.

Recently formed wind slabs and touchy persistent weak layers are making for tricky conditions. Conservative terrain selection remains important.

Summary

Confidence

Moderate - Due to the number of field observations on Sunday

Weather Forecast

A ridge of high pressure off the coast will slowly move eastward on Monday and should be established over the interior by Tuesday. Mostly cloudy conditions are expected for Monday with sunny breaks and light scattered flurries both possible. Alpine winds are expected to be light from the northwest in the morning but may become moderate in the afternoon. Freezing levels are expected to be below valley bottom during the over periods and stay below 1000m in the afternoons. A mix of sun and cloud is expected for Tuesday with light to moderate northwest winds in the alpine. Increasing cloudiness is expected for Wednesday in advance of a weak storm system that is currently forecast to arrive on Wednesday night.

Avalanche Summary

On Saturday, no natural avalanches were observed but several size 1 skier and explosive triggered avalanche were reported. Most of the skier triggered avalanches were 15-25cm thick wind slabs on north and east aspects at 2100-2300m. Explosives triggered several loose dry avalanches on northwest aspects in the alpine. On Friday, widespread natural avalanche activity up to size 3 was reported in throughout the region. This includes both storm slabs releasing down 30-60cm and persistent slabs failing down 70-100cm on the early January surface hoar layer. The storm slabs were failing on all aspects from 2000 to 2500m while the persistent slabs were failing on a variety of aspects around 1500-1900m. One persistent slab was also reported from 2300m on a southwest aspect. A skier accidently triggered a size 2 persistent slab avalanche on an east aspect at 1600m on the early January surface hoar layer down 70-80cm. Recently formed wind slabs and a reactive persistent slab are both expected to remain sensitive to human-triggering on Monday.

Snowpack Summary

Recent storm loading brings storm slab thickness to 20-40cm and up to 50cm in wind loaded areas. The recently destructive persistent weak layer from early January is now typically down 70-110cm in most places and has recently produced some large, destructive avalanches in the region. The layer is slowly getting harder to human trigger but is still quite reactive in snowpack tests and has the potential for wide propagations. In general, the lower snowpack below this layer is well settled and strong.

Problems

Wind Slabs

Recently formed wind slabs are lurking below ridge crests and behind cross-loaded terrain features and are expected to remain sensitive to human triggers. Weaknesses may also exist within or below the recent storm snow.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

The likelihood of triggering the buried weak layer is slowly dropping but if triggered, this layer can still produce large, destructive avalanches. A cornice failure or a small avalanche in motion has the potential step-down to a deeper weak layer.

Be cautious around steep open slopes and convex rolls at and below treeline where buried surface hoar may be preserved. >Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Feb 1st, 2016 2:00PM