Avalanche forecast

South Coast Inland

Jan 3 – 4, 2022Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Dangerous avalanche conditions and an unpredictable persistent weak layer demand a conservative approach to risk management.

If you do head out in the backcountry, you need to be able to avoid avalanche terrain and diligently manage your exposure to overhead hazard.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–3.5

    A weak layer of facets above a crust that formed in early December is found 70-150 cm deep. While it has become less likely to trigger avalanches on this layer, the consequences are large. The most suspect terrain would be shallow rocky start zones. 

    With an unpredictable problem such as this, it is critical for your group to practice good terrain travel techniques, be diligent in terrain selection, and to take a conservative approach to risk management.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–3

    Yesterday, a significant storm impacted the region. Up to 80cm of new snow has fallen in the past 48 hours. Strong southwest winds will have created deep deposits of slab in open areas. In sheltered areas, the new snow will form a touchy storm slab or loose dry problem where it is falling on a weak layer of near surface facets and in isolated areas surface hoar formed from prolonged cold temperatures earlier in the week. 

    The storm may be tapering but human triggering remains likely. This is a significant amount of new snow and the snowpack will need time to adjust to the new load.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Snowfall will continue into Monday. Tuesday evening marks a break in the storm, with a brief clearing proceeding the next system arriving Wednesday night.

Sunday Overnight: Continued snowfall, 10-20cm cm of accumulation expected. The Coquihalla may receive upwards of 30 cm with potential for local enhancement. Freezing levels rising to around 800m, dropping to 200m by early morning. Strong to extreme southwest winds easing moderate to strong.

Monday: Another stormy day, 10-15 cm of new snow accumulation. Winds shifting to the south in the moderate to strong range. Freezing levels rising in the afternoon around the Coquihalla to around 500m, staying near valley bottom elsewhere. Snowfall becoming lighter, another 5-15 cm expected overnight, freezing levels dropping to near valley bottom.

Tuesday: Lighter snowfall, 5-15 cm of accumulation. Light to moderate southwest winds, freezing levels at valley bottom. Possible clearing overnight, alpine temperatures dropping to -15 C.

Wednesday: A quieter day, cloud cover building into the afternoon as another system approaches from the pacific. Alpine temperatures around -13 C, rising into the afternoon. Light northwest winds at ridge-crest.

Avalanche Summary

Natural and human triggered avalanches are likely today. If you do observe any avalanche activity please let us know by submitting to the Mountain Information Network! ?

Over the past few weeks, we have been concerned about a potential persistent weak layer in the region. While most of the relevant observations have come from the neighbouring Sea To Sky region, similar types of avalanches were observed in northern parts of the region over a week ago. We suspect it would still be possible to trigger avalanches on this layer in isolated terrain features such as shallow rocky start zones around treeline elevations. 

Learn more about how this persistent weak layer is developing in our latest forecaster blog!

Persistent cold temperatures may have made cornices facetted and weak, highlighting the importance of avoiding overhead hazard and giving them a wide berth when travelling at ridge crest. Cornice failures can create a large load on the snowpack and trigger persistent weak layers.

Snowpack Summary

Yesterday, a significant storm impacted the region, bringing up to 80cm of new snow. Today snowfall will continue with up to 15 cm of accumulation. 

Reactivity may persist into today as southerly winds continue to create deep deposits of slab in open areas. In sheltered areas, the new snow has formed a touchy storm slab or loose dry problem where it has falling on an inherently weak layer formed from prolonged cold temperatures over the past week.

This layer is comprised of near surface facets, a thin sun crust on steep south facing aspects, and surface hoar in isolated areas at treeline and below. In many areas, these weak crystals are sitting on a firm bed surface of hard, wind effected snow and old windslabs.

A weak layer of facets (sugary snow) may be found over a crust that formed in early December (down 80-200 cm). In the neighbouring Sea to Sky region this layer has been particularly reactive at treeline and low alpine elevations, between 1800-2100 m. We have seen a decreasing trend in avalanche activity on this layer, but would be very cautious with a large amount of new load overlying this now deeply buried layer that has transitioned into a tricky low-probability high-consequence problem (see the problem description and travel advice for suggestions).

The lower snowpack is well settled with several early season crusts decomposing. Snowpack depth at treeline ranges from 160-250cm.

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.

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