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Avalanche Forecast

Archived

Nov 30th, 2018–Dec 1st, 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 exists. New forecaster blog HERE.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Mostly cloudy skies, cooling temperatures and dry conditions moving into the weekend. SATURDAY: Mostly cloudy with a trace of new snow/ alpine temperatures near -7/ generally light winds from the northeast/ freezing level 900 mSUNDAY: Cloudy/ alpine temperatures near -9/ ridgetop winds light from the northeast/ freezing levels 800 mMONDAY: Mix of sun and cloud with isolated flurries/ alpine temperatures -12/ ridgetop winds light from the northeast/ freezing levels valley bottom

Avalanche Summary

Natural avalanche activity has tapered off but human triggered avalanches remain possible, especially in places where a buried weak layer exists. The most significant report we received on Friday was a persistent slab avalanche that was triggered by explosives. This avalanche was a size 2.5 from a northeast aspect in an upper alpine bowl. The avalanche initiated from a shallow, rocky spot with good propagation. We suspect this avalanche failed on the buried crust at the base of the snowpack. This avalanche character is very similar to the human triggered size 3 mentioned below.Last Saturday, 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, 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 some reactivity in the South Columbia region. Suspect slopes and terrain are open bowls that host a rocky thin to thick snowpack in the alpine or upper treeline. 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.