Avalanche Forecast

Issued: Nov 29th, 2018 5:43PM

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

Avalanche Canada swerner, Avalanche Canada

There is a lot of uncertainty with the reactivity of the buried surface hoar layer down 40-80 cm. Human triggered avalanches are more likely at treeline and sheltered locations in the alpine where this weak layer exist. New forecaster blog HERE.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

The weather trend will start to stabilize as a high pressure system sets up, allowing dryer and cooler conditions. Clouds will linger through the weekend.FRIDAY: Mostly cloudy with scattered flurries and possible accumulations of new snow up to 10 cm / alpine temperatures near -6/ generally light winds from the SSW/ freezing level 1400 mSATURDAY: Cloudy with possible sunny periods/ alpine temperatures near -9/ ridgetop winds light from the North/ freezing levels 1100 mSUNDAY: Cloudy with a trace of new snow/ alpine temperatures -11/ ridgetop winds light from the northeast/ freezing levels near 800 m

Avalanche Summary

Natural avalanche activity will likely taper off as the weather pattern becomes more stable. On Wednesday, a few skier triggered avalanches were reported up to size 1.5 from N-E aspects above 1800 m. One of them failed on surface hoar and the other within the recent storm snow. Additional reports saw evidence of slab avalanches up to size 2.5 from steeper terrain features that failed during the storm (24-48 hrs old). The snowpack is still adjusting to the recent storm snow and the potential to trigger an avalanche remains, especially where the slab sits on buried surface hoar at treeline or sheltered (northerly) aspects in the alpine. Last Saturday (before the storm), a human triggered size 3 avalanche was reported in the region. This avalanche likely ran on the October crust, as it was reported as a full depth avalanche. Two reports on this avalanche can be found on the Mountain Information Network.

Snowpack Summary

The storm that arrived earlier this week distributed 40-80 cm of new snow by Wednesday morning with the higher accumulations in the Monashee Mountains. This recent snow sits on two layers of feathery surface hoar that are approximately buried 15 cm apart. One or both of these may be associated with a crust on south aspects. The surface hoar is mostly found at treeline and below, but it may be found in sheltered alpine areas.At the base of the snowpack is a crust that formed near the end of October. This crust is associated with sugary weak faceted crystals and has shown limited reactivity in the South Columbia region. However, it could come into play if triggered from a thinner snowpack area at higher elevations.Snowpack depths taper quickly with elevation, many areas have over 200 cm in the alpine, between 100-170 cm at treeline, and 10-100 cm below treeline.Check out the FORECASTER BLOG  as it will express our uncertainties with the current snowpack in this region.

Problems

Persistent Slabs

An icon showing Persistent Slabs
40 to 80 cm of recent storm snow overlies a weak layer of surface hoar (feathery crystals) and sun crust on steep south facing slopes. This problem may be more prevalent at treeline and in sheltered (northerly) alpine slopes.
Watch for signs of instability such as whumpfing, cracking, or recent avalanches.If triggered the slab may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
A crust at the base of the snowpack will result in large avalanches if triggered. Smaller avalanches may have the potential to step down to the basal layer.
Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.Avoid alpine bowls with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Nov 30th, 2018 2:00PM