Avalanche Forecast

Issued: Jan 14th, 2018 6:12PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Persistent Slabs and Loose Wet.

Avalanche Canada ghelgeson, Avalanche Canada

A Special Public Avalanche Warning is in effect in this region.Ongoing warm temperatures Monday are expected to initiate natural avalanche activity and further increase the likelihood of large human triggered avalanches.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Monday

Weather Forecast

The normal decrease in temperature with height has once again been replaced by an inversion. This classical pattern allows for cooler air to remain in the valleys while alpine temperatures rise to a degree or two above freezing. This setup should stick with us until Tuesday when warm air is expected to begin mixing into the valleys as an offshore front impacts the coast. The interior should remain mostly dry until a more robust system hits the south coast late Wednesday with precipitation spilling into the interior on Thursday.MONDAY: Scattered clouds in the morning, clearing throughout the day, freezing level at valley bottom with above freezing temperatures between 1700 m and 3000 m, light south wind, no snow expected. TUESDAY: Increasing cloud cover, freezing level initially at valley bottom, possibly rising as high as 2000 m. There may be a slight inversion, stay tuned for details. Moderate to strong south/southwest wind, trace of snow possible.WEDNESDAY: Broken cloud cover, freezing level at valley bottom, rising to 1300 m in the afternoon, moderate to strong southwest wind, trace of snow possible.

Avalanche Summary

We received observations Sunday of a natural avalanche cycle to size 3.5. These very large avalanches were running naturally on southwest, south and southeast facing alpine features and are thought to have been triggered by warming alpine temperatures and direct solar input. On Saturday natural avalanches to size 3 were reported from a wide variety of aspects and elevations. Some of the more notable occurrences were cornice failures on north and east facing aspects at upper elevations. Also of note was a size 2.5 avalanche that was remote triggered by a skier on a south/southeast facing feature around 2000 m, likely running on the early January weak layer.Widespread avalanche activity occurred Thursday and Friday with numerous reports of slab avalanches reacting to both explosive control work and human triggering. All aspects were involved as avalanches ran to size 3.0 on the early January interface. Some of the notable themes that are emerging from recent activity include accidental and remote triggering, 'step down' avalanches, avalanches on surprisingly low angle/supported terrain, and wide fracture propagations.

Snowpack Summary

The last series of storms left 50 to 70 cm of snow in their wake. Moderate to strong southwest winds previously formed wind slabs in upper elevation terrain. This snowpack is currently quite complex; there are four Persistent Weak Layers (PWL) that we are monitoring. The first PWL is known as the early January interface, it is 30 to 90 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects. It is thought to be widespread at all elevations bands and has produced numerous recent large avalanches. Another surface hoar layer from late December is just below the early January interface.The next PWL is the mid-December facet/surface hoar/crust combination that is now buried 70 to 150 cm deep and is most problematic at and below treeline. This interface is not thought to be present in the alpine.The most deeply buried PWL is the late November rain crust. It is found 125 to 200 cm below the surface and has gone dormant for the time being.

Problems

Persistent Slabs

An icon showing Persistent Slabs
Warm alpine temperatures and direct solar input Sunday produced very large natural avalanches and that activity is expected again Monday.  Avoid avalanche terrain, especially in the alpine, as the snowpack adjusts to recent loading and warmth.
Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Numerous large avalanches have run on these layers in well supported, treed terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 4

Loose Wet

An icon showing Loose Wet
Loose wet avalanches are expected to be problematic again Monday as previously cold snow is subjected to above freezing temperatures and strong solar input.
Loose avalanches in motion may step down and initiate large destructive slab avalanches.Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Avoid exposure to terrain traps where the consequences of any avalanche will be more serious.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Jan 15th, 2018 2:00PM