Avalanche Forecast

Issued: Apr 2nd, 2017 3:23PM

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

cgarritty, Avalanche Canada

South Columbia.

The sun will be out in force on Monday. As it rapidly warms the snowpack, there will be an increasing likelihood of highly destructive persistent slab avalanches that run full path. Cornice falls are likely triggers.

Summary

Confidence

Moderate -

Weather Forecast

Monday: A mix of sun and cloud. Light northwest winds. Freezing level to 1700 metres with alpine temperatures around -5.Tuesday: Cloudy with sunny periods. Light southwest winds. Freezing level to 1900 metres with alpine temperatures around -3.Wednesday: Mainly cloudy. Light to moderate south winds. Freezing level to 2300 metres with alpine temperatures around 0 to +1.

Avalanche Summary

Reports from Saturday include numerous observations of storm slabs releasing from Size 1.5-2. Ski cutting, skier traffic, and explosives account for the majority of these occurrences, however one Size 3 storm slab was reported to have run naturally. One highly notable observation details a Size 3.5-4 deep persistent slab that was triggered by a large cornice fall. This slide ran all the way to ground and reached the end of its historical runout. It featured a crown fracture of up to 4 metres at its deepest. North to west aspects showed the most activity in reports and all activity occurred above about 2000 metres.Reports from Friday showed several recent (12-36 hour old) persistent slab releases to Size 3 with natural storm slab and cornice triggers. Two of these occurred on southeast aspects. Improved visibility also revealed evidence of numerous storm slabs and wind slabs having released from Size 2-3 over the same time period.Looking forward, anticipate a stark change in the snowpack from morning to afternoon as solar warming breaks down surface crusts and promotes instability in a wide range of avalanche problems over the course of each day.

Snowpack Summary

10-30 cm of new snow now overlies a crust below about 2100 metres (higher on solar aspects) and moist snow below about 1800 metres. Below the new snow interface, storms over the past week brought 40-60 cm of snow to the region. Several other crusts as well as moist snow are likely to exist within this storm snow, mainly at lower elevations and on solar aspects. Moderate to strong southwest winds during and since the storm formed wind slabs on leeward slopes as well as fragile cornices along ridgelines. 90-130 cm of accumulated snow now overlies a more widespread rain crust below 2000 m and sun crust on solar aspects at higher elevations. At higher elevations, the February weak layers are down 160 cm to over 2 metres and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases continue to be reported and these deeply buried weaknesses remain a serious concern as solar radiation and warming temperatures begin to penetrate the snowpack at increasingly higher elevations.

Problems

Persistent Slabs

A cornice fall or smaller slab avalanche could trigger large, destructive avalanches on deeply buried weak layers. The likelihood of this happening will increase as solar warming weakens unstable cornices and storm slabs over the course of the day.

Cornices or smaller slab avalanches could step down to deeper layers resulting in large avalanches.Recognize and avoid runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 4

Storm Slabs

Recent snow and wind have formed storm slabs that may remain reactive to human triggering. This problem is more pronounced in wind affected areas at higher elevations, so be vigilant for signs of recent wind loading.

Minimize your exposure to sun exposed slopes.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Loose Wet

Daytime warming will progressively deteriorate the surface of the snowpack at lower elevations and especially on solar aspects. Snow that becomes moist will have the tendency to sluff from steep terrain, either naturally or with a human trigger.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Apr 3rd, 2017 2:00PM