Avalanche Forecast

Issued: Apr 20th, 2018 4:02PM

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

Avalanche Canada cgarritty, Avalanche Canada

Avalanche danger will rise in sync with new snow accumulations on Saturday. Keep an eye on new snow depths and expect wind to create thin but touchy new slabs.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Friday night: Flurries bringing about 5 cm of new snow. Strong southwest winds.Saturday: Mainly cloudy with continuing flurries bringing about 5 cm of new snow. Strong west winds. Freezing level to 1600 metres with alpine high temperatures around -5.Sunday: A mix of sun and cloud. Light northwest winds. Freezing level to 1600 metres with alpine high temperatures around -6.Monday: Sunny. Moderate south winds. Freezing level rising to 2200 metres and climbing overnight. Alpine high temperatures around 0.

Avalanche Summary

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 Sunday and late last week showed a pattern of heightened cornice failure activity, with several cornice releases triggering large persistent slabs and wind slabs.Looking forward, continuing warm temperatures will be maintaining elevated chances of loose wet avalanche and cornice activity before another round of light snowfall introduces new surface instabilities over Friday night and Saturday.

Snowpack Summary

New snow is forecast to accumulate above a new melt freeze crust that can now be found on the 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 surface 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. Recent wind slabs on the surface at higher elevations are expected to be on a similar stabilizing trend.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

Wind Slabs

An icon showing Wind Slabs
Light new snow and increasing winds will begin to build thin new wind slabs in the lee of exposed terrain over Friday night and Saturday. There is a possibility for the sun to poke out and destabilize the new snow in the afternoon.
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

Possible - Likely

Expected Size

1 - 1.5

Cornices

An icon showing Cornices
Several large cornice failures have been reported in recent days. Large cornice collapses have the potential to trigger a deep weak layer near the base of the snowpack, which would result in a very large and destructive 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

Unlikely - Possible

Expected Size

2 - 3.5

Valid until: Apr 21st, 2018 2:00PM

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