Avalanche Forecast

Issued: Jan 3rd, 2020 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada ahanna, Avalanche Canada

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Recent snow and strong winds in the alpine and treeline Friday night have formed deep pockets of touchy storm slab. Caution solar triggering of the new snow when the sun comes out Saturday morning.

Summary

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Forecast snowfall amounts are uncertain.

Weather Forecast

Friday night: Heavy snowfall tapering overnight accumulating 10-15 cm. Wind increasing to strong southwest, approaching extreme at ridgetop. Alpine low temperature around -12 C. Freezing levels rising to 1000 m by 10 pm, then back down to valley bottom overnight.

Saturday: Sunny in the morning, cloud increasing in the pm, moderate southwest wind, alpine high temperatures around -9 C.

Sunday: Mix of sun and cloud with isolated flurries accumulating up to 5 cm, light to moderate west wind, alpine high temperatures around -7 C.

Monday: Mix of sun and cloud with isolated flurries accumulating up to 5 cm, strong southwest wind, alpine high temperatures around -7 C.

Avalanche Summary

A widespread avalanche cycle up to size 3 was reported from the Howson range during the storm on Friday. This cycle is likely to be ongoing throughout the southern part of the region where more than 40 cm of snow fell on Friday.

Before the storm, reports of persistent slab avalanches associated with buried surface hoar were trickling in, from Ashman, Telkwa and Howson areas. They included natural and artificially triggered avalanches ranging in size from 1.5-3, and have occurred on all aspects mainly at treeline but also in the alpine. The new snow load will increase the size and consequences of avalanches on these layers.

Snowpack Summary

40-60 cm of new snow from the past 36 hours has been highly wind affected overnight by strong to extreme winds. Expect to find deep wind loaded pockets below ridgetops and the lee sides of features all the way down to treeline. Below treeline, soft snow will be found down at least as far as 1000 m, where freezing levels may have creeped up to overnight.

A couple of layers of surface hoar are now buried 50-100 cm below the surface in sheltered areas around treeline. Reports of avalanche activity on these layers suggest they have recently become active, and the new snow load will provide additional stress.

Terrain and Travel

  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Storm Slabs

An icon showing Storm Slabs

40-60 cm of new snow followed by strong to extreme winds Friday night have likely formed deep pockets of storm slab in lee features in the alpine and treeline. The new snow will be sensitive to triggering when the sun comes out on Saturday.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs

The added stress and slab character of the new snow load may increase the reactivity of the layer, which is now buried 50-100 cm deep. Human triggering of weak layers at this depth is definitely possible and would result in large, high consequence avalanches.

Aspects: All aspects.

Elevations: Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Jan 4th, 2020 5:00PM