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Avalanche Forecast

Archived

Nov 29th, 2018–Nov 30th, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

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.

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

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.