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

Low - Due to the number of field observations

Weather Forecast

Monday: Mainly sunny. Light southeast winds. Freezing level to 2200 metres and rising overnight. Alpine high temperatures around 0.Tuesday: Mainly sunny. Light south winds. Freezing level to 2700 metres with alpine high temperatures around +3. Weak overnight cooling.Wednesday: Mainly sunny. LIght to moderate southwest winds. Freezing level to 3100 metres with alpine high temperatures around +5. Weak overnight cooling.

Avalanche Summary

Several smaller (size 1.5) natural wind slab avalanches were observed in the region on Saturday. These occurred primarily on northwest aspects above 2400 metres.Reports from Thursday were limited to a couple of size 2 storm and wind slabs, 30 and 50 cm deep, respectively. The storm slab released naturally while the wind slab was ski cut from a steeper north aspect in the alpine.Tuesday's reports 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. Observations from late last week also showed a pattern of heightened cornice failure activity. 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

10-15 cm of new snow has been blown into wind slabs on a variety of aspects due to variable strong winds. The wind affected snow overlies a melt freeze crust found on the previous surface on all but north aspects above about 2200 metres. Below it, about 50-70 cm of settled storm snow overlies a supportive crust which shares similar distribution to the upper crust.Within this storm snow there are a few different crusts with the shallowest of these (down about 20-40 cm) now a limited concern as recent warm temperatures have promoted settlement and bonding in the upper snowpack.With warm daytime temperatures and poor overnight recovery of cold temperatures, there is some lingering concern around the mid-March weak layer in the alpine where it is found 90 to 120 cm deep. This buried crust/surface hoar layer was widely reactive but is now 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 reactive to very large triggers.

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

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

Elevations: All elevations.

Likelihood

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
New snow and variable strong winds have formed wind slabs on a variety of aspects. Slabs may remain reactive to human triggering over the near term and reactivity may increase with daytime warming on Monday.
Be careful with wind loaded pockets near ridge crests and roll-overs.Minimize your exposure to sun exposed slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

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