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Avalanche Forecast

Archived

Jan 5th, 2022–Jan 6th, 2022

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

Watch for the formation of fresh wind slabs in exposed terrain as southwest wind picks up ahead of the next storm on Thursday. Snow amounts appear modest for Thursday, but watch for hazard to increase through the day, especially in areas that receive more than 20 cm of new snow.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

A storm impacting the region offers a nice refresh of cold snow accompanied by strong wind largely out of the south.

WEDNESDAY NIGHT: Freezing level at valley bottom, trace of snow possible, light variable wind.

THURSDAY: Overcast, freezing level at valley bottom, moderate to strong wind largely out of the southwest, snow beginning in the morning, 2 to 8 cm expected during the day with another 10 to 20 cm expected Thursday night.

FRIDAY: Overcast, freezing level at valley bottom, strong southwest wind, 5 to 15 cm of snow possible.

SATURDAY: Broken cloud cover, freezing level at valley bottom, moderate to strong west wind, 1 to 3 cm of snow possible.

Avalanche Summary

Avalanche activity in the storm snow was diminished Tuesday, but avalanche control work produced avalanches to size 1.5 that were most prevalent in wind loaded upper elevation terrain features.

Lots of natural (and a few human triggered) storm slabs and loose dry avalanches to size 2 were observed Monday, primarily on northeast facing terrain.

In the South Columbias, the only reported activity on the early December crust/facet interface in the last week was a natural size 2.5 avalanche that released in a shallow rocky northeast facing feature at 2300 m. The North Columbia also has very limited recent avalanche activity on the crust, but it has been quite a bit more active in the regions to the south and east, more details and photos of that activity can be found here.  

Snowpack Summary

The weekend storm produced 20 to 50 cm of storm snow accompanied by wind that was quite variable, but mainly out of the south. Early reports from folks exploring in the alpine report that there was less wind loading than expected.

We're actively monitoring the early December crust. In some places it's scoured and on the surface, while in wind loaded terrain features it can be found as deep as 150 cm below the surface. It consists of faceted grains above a bulletproof crust formed by the Atmospheric Rivers of early December. Avalanches failing on this interface have the potential to be very large. 

Terrain and Travel

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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.