Avalanche Forecast

Issued: Mar 4th, 2018 4:25PM

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

shorton, Avalanche Canada

South Coast Inland.

A week of benign weather will allow the snow to gradually gain strength. Use caution around wind loaded slopes where the recent snow may still be reactive to human triggers.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Mainly cloudy with isolated flurries and 2-5 cm of new snow, light west wind, freezing level rising to around 800 m.TUESDAY: Mostly sunny, light wind, freezing level rising to around 1000 m.WEDNESDAY: Sunny, light to moderate west wind, freezing level rising to around 1300 m.

Avalanche Summary

On Saturday, one natural size 2 slab was observed on a south aspect at 1900 m in the Duffey area and another smaller slab was reported on a steep wind-loaded feature in the Coquihalla area. Dry loose avalanches were reported in steep terrain in the Coquihalla area and wet loose avalanches were observed throughout the region in steep south-facing terrain.On Friday, wind slabs were sensitive to skier triggering to size 2 on north and northeast facing slopes around 2000 m. These slabs were 10 to 25 m wide with crowns averaging 40 cm in depth. On Thursday wind loaded features produced natural avalanches to size 2.5. Several natural wind slab avalanches to size 2 were observed on steep north facing alpine terrain. Control work produced avalanches to size 2 in steep unsupported terrain.

Snowpack Summary

The Coquihalla picked up a surprise 35 to 45 cm on Friday which is now hiding previously formed wind slabs. Mainly southerly winds formed these wind slabs as they interacted with up to 120 cm of storm snow that fell last week. All of the new snow rests on the February 23 weak layer. The February 23 weak layer is now 80 to 120 cm deep in the southern part of the region and about 40 cm deep in northern parts of the region. This interface consists of wind hardened snow, facets, a sun crust on solar aspects and surface hoar that is present at and below treeline. Compression tests preformed Friday continue to show planar results at this interface. The mid and lower snowpack are well settled and strong.Variable winds in the past month have created cornices on many alpine ridgelines. They will become touchier as they grow in size, as temperatures rise, and as the strong late-winter sun shines down upon them on clear days.

Problems

Wind Slabs

The south of the region picked up 40 cm of new snow Friday with light easterly winds. Up to 120 cm of snow has fallen in the last week, and it all rests on a weak layer which may still be susceptible to human triggering.

Avoid wind loaded terrain features, especially near ridge crests and roll-overs.The recent snow is now hiding wind slabs that were recently sensitive to human triggering.Brief periods of sun could quickly initiate natural avalanche activity.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Cornices

Continued snowfall and strong wind from around the clock has formed large cornices on many ridgelines. Cornices are inherently unstable, unpredictable, and demand respect, especially when the sun is out.

Watch out for overhead hazards, such as cornices, which could trigger slabs on slopes below.Give cornices a wide berth when travelling on or below ridges.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2.5

Valid until: Mar 5th, 2018 2:00PM