Avalanche Forecast

Issued: Apr 19th, 2018 4:41PM

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

Avalanche Canada cgarritty, Avalanche Canada

Clues to mountain hazards are currently quite apparent on the surface. Tune in to overhead hazards, moist snow, and lingering wind slabs as you travel on Friday.

Summary

Confidence

Moderate -

Weather Forecast

Friday: Mainly cloudy with isolated flurries and a trace of new snow, increasing overnight. Light south winds becoming strong at ridgetop. Freezing level to 1900 metres with alpine high temperatures around -2. Weak overnight cooling.Saturday: Cloudy with continuing flurries bringing about 5 cm of new snow. Light to moderate west winds. Freezing level to 1700 metres with alpine high temperatures around -3.Sunday: Mainly sunny. Light northwest winds. Freezing level to 1700 metres with alpine high temperatures around -4.

Avalanche Summary

Reports from Tuesday included observations of numerous natural wind slab release from size 1-2 on north through east aspects in the alpine. A skier triggered size 2 storm slab resulted in a near miss. Another recent very large (size 3.5) storm slab was also observed to have released on a large, wind-loaded alpine feature. Reports from Monday were limited by poor visibility but included one small (size 1, 20 cm deep) ski cut wind slab as well as skier-triggered loose snow releases on steeper slopes. The rough dividing line between loose wet and loose dry activity was about 2000 metres.In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity. Reports of 'bus sized' blocks found in debris as well as a suspected cornice-triggered size 4 wind slab release should keep these looming giants top of mind.Looking forward, continuing warm temperatures will be maintaining elevated chances of loose wet avalanche and cornice activity before another round of snowfall introduces new surface instabilities over Friday night and Saturday.

Snowpack Summary

About 50-70 cm of rapidly settling storm snow overlies a supportive crust on all aspects to at least 2300 m (and possibly higher on south aspects).Within this storm snow there are a few different crusts with the shallowest of these (down about 2-40 cm) becoming a diminishing concern as recent warm temperatures have promoted settlement and bonding in the upper snowpack. Recently formed wind slabs on the surface at higher elevations are expected to be on a similar stabilizing track.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 90 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but is now 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 cornice collapse.Deeper persistent weak layers from December and January are generally considered dormant at this time but may be starting to become reactive to large triggers, such as a cornice collapse.

Problems

Loose Wet

An icon showing Loose Wet
Continued warm temperatures are expected to maintain elevated likelihood of loose wet avalanche activity, especially on steep slopes at lower elevations. Loose wet releases may occur naturally or with a human trigger.
Manage your sluff and be extra cautious where long slopes allow for more snow entrainment.Use extra caution on slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Cornices

An icon showing Cornices
Large cornice failures have been reported in the past week and warm temperatures continue to weaken cornices. A cornice collapse may have the potential to trigger a deep weak layer resulting in a very large and destructive avalanche.
Give cornices a wide berth when traveling on or below ridges.Cornices weaken with sun and daytime heating. Minimize your exposure to large cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

An icon showing Wind Slabs
Lingering wind slabs formed after the last snowfall my still be reactive to human triggering in isolated areas. The main concern is for steep wind-loaded slopes near ridge crests.
Be careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2.5

Valid until: Apr 20th, 2018 2:00PM

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