Avalanche Forecast

Issued: Apr 22nd, 2018 4:32PM

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

Avalanche Canada cgarritty, Avalanche Canada

The first sustained warmup of spring is finally here. Surface instabilities and cornice hazards should be firmly on your radar as you travel. Expect stability to deteriorate over the day.

Summary

Confidence

Moderate -

Weather Forecast

Monday: Mainly sunny. Light southwest winds. Freezing level to 2100 metres and climbing overnight. Alpine high temperatures around 0.Tuesday: Mainly sunny. Light to moderate southwest winds. Freezing level to 2500 metres with alpine high temperatures around +2. Weak overnight cooling.Wednesday: Sunny. Light west winds. Freezing level to 3100 metres with alipne high temperatures around +4. Weak overnight cooling.

Avalanche Summary

Decreasing traffic in the mountains has limited avalanche observations over the past few days.Reports from Thursday included more evidence of the recent natural avalanche cycle described below, with several additional recent storm and wind slab releases to size 2.5 observed. Sun and wind were identified as prominent triggers.No new avalanches were reported in the Cariboos on Wednesday, but reports from the North Columbias 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 observed to have released on a large, wind-loaded alpine feature. Tuesday's reports included observations of several large (size 2) wind slabs that released naturally as a result of recent strong winds.Reports from just over a week ago showed a pattern of heightened cornice failure activity, with several releases triggering large persistent slabs and wind slabs.Looking forward, a period of increasing warming, full sun, and warm overnight temperatures will be maintaining elevated chances of cornice and loose wet avalanche activity.

Snowpack Summary

About 5-10 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 50 cm of settled storm snow covers another supportive crust which shares similar distribution to the upper crust.Within this storm snow there are several different crusts with the shallowest of these (down about 25 cm) now a limited concern after 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 reactivity at the mid-March persistent weak layer in the alpine where it is found 100 to 150 cm deep This buried crust/surface hoar layer may still be capable of producing large avalanches if triggered with a heavy load, such as a cornice collapse.Deeper persistent weak layers from December and January may be starting to become reactive to very large triggers. A recent cornice collapse is believe to have initiated a slab release on an early season layer, 300 cm deep.

Problems

Loose Wet

An icon showing Loose Wet
Daytime warming and sun exposure will promote natural loose wet avalanche activity on Monday - especially around steep, sun-exposed terrain.
Minimize exposure when the solar radiation is strong, especially if snow is moist or wet.Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Cornices

An icon showing Cornices
Weak overnight cooling, warm daytime temperatures and strong sun will be increasing the chance of cornice failures in coming days. Cornice falls may have potential to trigger a weakness at the base of the snowpack and cause a very large avalanche.
Cornices weaken with sun and daytime heating. Minimize your exposure to large cornices overhead.Give cornices a wide berth when traveling on or below ridges.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

An icon showing Wind Slabs
Light new snow and strong winds have likely formed thin new wind slabs in the lee of exposed terrain. Slabs may remain reactive to human triggering over the near term and reactivity may increase with daytime warming on Monday.
Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Apr 23rd, 2018 2:00PM

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