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Avalanche Forecast

Archived

Jan 18th, 2023–Jan 19th, 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.

Rogers Pass and the surrounding Columbia Mtns have a weak basal snowpack this season, which is making all snow professionals work hard to manage avalanche problems that are atypical of these areas.

Drop your desires down a notch; ski/ride to the conditions we have this year.

Confidence

Moderate

Avalanche Summary

A field team today triggered a couple of size 1.0 slab avalanches on small convex rolls at the 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

A couple of weak fronts pass our area this evening, giving a few cms of new snow, with light ridgetop winds, and alpine temps dropping to -9*C.

This will be followed by a ridge of high pressure over our area until the weekend. Giving a mix of sun and cloud, seasonal temps (-12 to -6*C)and light winds.

Another cold front on Saturday will bring increased wind and up to 10cm of new snow.

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.