Avalanche Forecast

Archived

Jan 20th, 2023–Jan 21st, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

New snow and wind will continue to add to the load over the early January surface hoar layer. Be extra cautious in windloaded lee terrain, where this layer may be getting buried deeply enough to produce large avalanches.

Confidence

Moderate

Avalanche Summary

On Friday, we received a report of a skier triggered size 1.5 windslab at the entrance to Nicky's notch.

On Thursday, there was a report of a size 1 skier triggered slab avalanche near the Dome Col, which was was suspected to have failed on one of the surface hoar layers in the upper snowpack.

On Wednesday, a field team today triggered a couple of size 1.0 slab avalanches on small convex rolls at treeline - one of these failed on the Jan 3rd surface hoar layer down 35cm. There was also a MIN report of a skier triggering a similar size 1.0 slab on the Jan 3rd layer on McGill shoulder.

In neighboring areas there are continued reports of isolated human triggering of the recently buried surface hoar layers, as well as natural/explosive triggering of the deep persistent facet layer.

Snowpack Summary

New snow and wind will continue to build the slab over the early January surface hoar layers. These two surface hoar (SH) layers, present in the upper 40cm, have been reactive to human triggering recently.

Recent warm temperatures have left a melt-freeze crust at or near the surface below ~1600m.

The mid-pack facets are slowly rounding and gaining strength, while the basal facets and Nov 17 facet/SH/crust weakness are still reactive when isolated in snowpack tests.

Weather Summary

We're going to get a minor blip of snow (up to 10cm) and gusty SW winds on Saturday, with the passage of a cold front. After that ground hog day continues well into next week, with the same old mixed bag of mostly cloudy skies, isolated flurries, seasonal temps (-10 to -15*C) and light winds.

Terrain and Travel Advice

Be especially cautious as you transition into wind affected terrain.
Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.