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Avalanche Forecast

Archived

Mar 7th, 2020–Mar 8th, 2020

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

Regions

South Rockies.

Start small and watch for signs of instability or indications that new snow has settled into a reactive slab over the old snow surface on Sunday. Expect new snow to become especially touchy on southerly slopes if the sun makes an appearance.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Saturday night: Cloudy with continuing flurries and up to 5 cm of new snow. Light to moderate southwest winds, becoming strong at ridgetop.

Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate southwest winds, becoming strong at ridgetop. Alpine high temperatures around -9.

Monday: Sunny. Light southwest winds. Alpine high temperatures around -8.

Tuesday: A mix of sun and cloud with cloud increasing over the day. Moderate to strong southwest winds. Alpine high temperatures around -4.

Avalanche Summary

Preliminary reports from Saturday in the neighbouring Lizard Range and Flathead mainly show new snow reacting to skier traffic and explosives control as dry loose sluffs, reaching size 2. Soft slab formation was noted in wind-affected features at ridgecrest. Similar conditions are expected to exist in areas of the South Rockies that saw 20 or more cm of new snow.

Elevated avalanche danger is expected to be maintained through Sunday as the new snow settles into more consolidated storm slabs that only gradually begin bonding with the previous snow surface. Periods of sunshine may also promote natural avalanche activity.

Snowpack Summary

By the time snowfall eases off Saturday night, new snow totals over the region may reach up to 30 cm. The new snow has buried recent wind slabs and wind effect in exposed terrain as well as sun crust on solar aspects and temperature crust up to 1700 m on all other aspects. The new snow is not expected to bond well with any of these surfaces over the short term.

A thick rain crust currently sits 40-80 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17. The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Avalanche hazard is expected to to increase througout the day, think carefully about your egress.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.