North Rockies Avalanche Forecast - December 22, 2020

Exercise restraint as skies clear and visibility improves this week. Avalanche activity during the stormy period has been steady, with a tricky set of failure planes in play. Ease cautiously into low consequence terrain and watch for signs of instability.

Tuesday

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Alpine - Considerable
Treeline - Considerable

Below treeline - Considerable

Wednesday

Alpine - Considerable
Treeline - Considerable

Below treeline - Considerable

Thursday

Alpine - Considerable

Treeline - Considerable
Below treeline - Considerable

Avalanche Summary

A report from the Tumbler Ridge rail corridor on Saturday detailed evidence of a 24-48 hour-old widespread natural avalanche cycle producing avalanches up to size 3 (very large) This cycle appeared to be linked directly to recent southwest winds. Subsequent explosives control yielded smaller, thinner wind slab releases.

Pine Pass reports on Friday (courtesy of your local AvCan field team) included natural, accidental, and remotely triggered avalanches up to size 2.5. That's a big slide to get tangled up in -- one party of three were caught and partially buried (one up to the neck) or fully buried (with a deployed airbag).

Slides were running at the bottom or the recent storm snow (down 40 cm) or last week's crust (65 cm deep). There was also a size 3 reported from Renshaw. Observations have been limited by lack of visibility.

Snowpack Summary

The upper snowpack is made up of new or recent snow from a parade of storms over the past week. A recent bout of strong southwest wind redistributed much of this snow in exposed areas at higher elevations, forming wind slabs in the process.

In some areas in the north (Pine Pass, possibly Wolverine) there is a weak layer of surface hoar near the bottom of this recent snow - now as deep as 60 or 80 cm. In some areas this layer may present as a combo of crust and faceted snow. This variable layer continues to react in snowpack tests and slope cuts and should figure into your terrain decisions wherever wind slabs aren't the dominant concern.

The mid and basal snowpack feature a variety of crusts. Recent reports have not highlighted them as a problem but they may be a concern in areas of the region with a shallow snowpack.

Snow depths are approaching 200 cm around Pine Pass, the MacGregors, and McBride and around 100 cm in the northeast around Tumbler Ridge.

Weather Forecast

MONDAY NIGHT - Cloudy with isolated flurries. Light north winds.

TUESDAY - Becoming sunny. Light northwest winds increasing over the day and overnight. Alpine high temperatures around -12.

WEDNESDAY - Sunny. Moderate to strong southwest winds. Alpine high temperatures around -5, possibly cooler at lower elevations under a mild temperature inversion.

THURSDAY - A mix of sun and cloud. Light to moderate southwest winds. Alpine high temperatures around -5, possibly cooler at lower elevations under a mild temperature inversion.

Travel and Terrain Advice

  • Use small low consequence slopes to test the bond of the new snow.
  • Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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A map of the North Rockies. - Avalanche Canada image
© Copyright Alaska Highway News

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