Avalanche Forecast
Issued: Jan 5th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
There is some uncertainty as to how the recent storm snow is bonding to the old surface and how buried weak layers have reacted under the new load.
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Summary
Confidence
Weather Forecast
Sunday night: Flurries accumulating up to 5 cm, moderate west wind, alpine temperatures around -12 C.
Monday: Sunny with cloudy periods, light to moderate west to northwest wind, alpine high temperatures around -12 C.
Tuesday: Mix of sun and cloud with isolated flurries, light variable wind, alpine high temperatures around -10 C.
Wednesday: Mix of sun and cloud with isolated flurries, light to moderate variable wind, alpine high temperatures around -10 C.
Avalanche Summary
A widespread avalanche cycle up to size 3 was reported from the Howson range during the storm on Friday with avalanches up to size 2 observed below treeline. This cycle is likely to have occurred throughout the southern part of the region on Friday and Saturday, 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 recent storm snow has been highly wind affected in the alpine. Expect to find deep wind loaded pockets below ridgetops and the lee sides of exposed features.
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 before the last storm suggest they may be active, especially now that they are under additional snow load.
Terrain and Travel
- Closely monitor how the new snow is bonding to the old surface.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Uncertainty is best managed through conservative terrain choices at this time.
Problems
Storm Slabs
40-60 cm of recent storm snow and strong winds have likely formed deep pockets of storm slab in lee features in the alpine and treeline. Watch for solar triggering of recent snow on solar aspects during periods of sun. Even after natural storm cycle avalanche activity starts to taper off, storm slab avalanches will remain sensitive to human triggering.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A couple layers of surface hoar are now buried 50-100 cm deep, with uncertainty around their distribution outside of the treeline elevation band. There is uncertainty as to how the buried weak layers have reacted to the new load of storm snow. 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
Expected Size
Valid until: Jan 6th, 2020 5:00PM
