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Avalanche Forecast

Archived

Jan 3rd, 2020–Jan 4th, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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 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

Northwest Inland.

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.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.