Avalanche Forecast

Issued: Apr 21st, 2018 3:55PM

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

cgarritty, Avalanche Canada

South Columbia.

New snow accumulations are likely to become increasingly reactive as warming and solar radiation increase over the day. Increase your caution around sun-exposed slopes as well as wind loaded areas.

Summary

Confidence

Moderate -

Weather Forecast

Sunday: A mix of sun and cloud. Light northwest winds. Freezing level to 1700 metres with alpine high temperatures around -5.Monday: Sunny. Light south winds. Freezing level to 2400 metres and climbing overnight. Alpine high temperatures around +1.Tuesday: Mainly sunny. Light south winds. Freezing level to 3000 metres with alpine high temperatures around +5.

Avalanche Summary

A few natural storm and wind slab releases were observed on Thursday, ranging from size 1-2.5. One of these was a size 2 slab triggered by a loose wet avalanche while the 2.5 wind slab was triggered by natural ice fall on a north aspect at 2200 metres. It featured a 45 cm crown fracture.Reports from Wednesday included an observation of a natural size 2 cornice release from a north aspect in the north of the region. Numerous natural loose wet avalanches were also observed on sun-exposed aspects in the Monashees.Tuesday's reports showed numerous small (size 1) storm slabs releasing both remotely and with ski cutting. Crown fractures were in the 35-40 cm range and activity was observed at all elevations and on all but west aspects.In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity.Looking forward, sunshine and warming temperatures are expected to promote both natural and human-triggered avalanches limited to the new snow. The same warming may also cause natural cornice collapses.

Snowpack Summary

About 15-20 cm of new snow has accumulated above a melt freeze crust found on the previous surface on all but north aspects above about 2200 metres. Below it, About 70-100 cm of rapidly settling storm snow overlies another supportive crust which shares similar distribution to the upper crust.Within the upper snowpack there are now a few different crusts with the shallowest of these (down 30-50 cm) now a limited concern as warm temperatures have promoted settlement and bonding in the upper snowpack.With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains some lingering concern around the mid-March persistent weak layer in the alpine where it is found 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but is likely trending towards dormancy. It should be kept in the back of our minds for its capability to produce large avalanches should it be triggered with a heavy load such as a snowmobile or cornice collapse.Deeper persistent weak layers from December and January are considered dormant at this time.

Problems

Wind Slabs

New snow and strong winds will have formed new wind slabs in the lee of wind-exposed terrain. Slabs are likely to remain reactive over the near term and reactivity is likely to increase with sunshine and daytime warming on Sunday.

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

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Cornices

Large cornice failures have been reported in the past week and cornices will weaken with daytime warming on Sunday. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.

Cornices become weak with daytime heating. Minimize your overhead exposure.Give cornices a wide berth when travelling on or below ridges.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1.5 - 3

Loose Wet

Daytime warming and sun exposure will promote natural loose wet avalanche activity on Sunday - especially around steep sun-exposed terrain.

Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.Minimize exposure when the solar radiation is strong, especially if snow is moist or wet.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 1.5

Valid until: Apr 22nd, 2018 2:00PM