Avalanche Forecast

Archived

Jan 19th, 2023–Jan 20th, 2023

Alpine

Natural avalanches unlikely, human triggered possible.

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.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

The weak basal facets and persistent weak layers within the upper snowpack continue their lurking ways around Rogers Pass.

Keep sticking with your conservative program; ride supported terrain, respect others by not dropping in on top of them, and come home safe.

And if you're skiing on glaciers, the thin snowpack is barely hiding open crevasses. Travel with care!

Confidence

Moderate

Avalanche Summary

On Wed 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.

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

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

Two surface hoar (SH) layers, present in the upper 40cm, are potential failure planes in areas where the surface snow has become slabby (ridgecrests, immediate lee features).

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

-ahem....- is anyone awake in the weather-making department? A minor blip of snow and gusty SW winds on Sat, but otherwise much of the same mix of cloud, flurries, and light winds.

Fri: clouds with sun, nil snow, Alp high -5*C, 800m FZL, light W ridge winds

Sat: flurries, 10cm snow, Alp high -4*C, 800m FZL, mod/gusting strong SW winds

Terrain and Travel Advice

Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.