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Avalanche Forecast

Archived

Mar 24th, 2019–Mar 25th, 2019

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

Regions

South Rockies.

Small loose wet avalanches may gather mass, become much larger, and run farther into low angle terrain than expected.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY NIGHT: Cloudy / Light, southwesterly winds / Alpine low -4 C / Freezing level 1200 m.MONDAY: Mix of sun and cloud / Light, southwesterly winds / Alpine high 2 C / Freezing level 2000 m.TUESDAY: Cloudy with flurries (rain below approx. 1500 m.); 3-5 mm. / Strong, southwesterly winds / Alpine high 0 C / Freezing level 1700 m.WEDNESDAY: Mostly cloudy / Light, easterly winds / Alpine high -1 C / Freezing level 1600 m.

Avalanche Summary

Natural avalanche activity has tapered off, but concern remains for human triggering deep persistent slab avalanches; especially in rocky alpine terrain with a shallow or highly variable depth snowpack.On Thursday, there were numerous reports of skiers triggering what started as small loose wet avalanches and then gathered mass and entrained the entire snowpack to the ground running much further than expected, up to size 2. Check out this video from our South Rockies Field Team HERE.A report from our South Rockies Field Team on Tuesday in the Elk Valley described numerous natural persistent slab releases reaching size 2 (large) on southeast aspects at around 2200 m. Further to this activity, any sun-exposed snow became isothermal (slushy and cohesionless), and large whumpfs that collapsed the basal snowpack were triggered during ski touring. Check out their video HERE.

Snowpack Summary

The prolonged warm spell has transitioned sun exposed slopes in the alpine and all aspects at treeline and below towards becoming isothermal (0 C throughout the snowpack). In these areas that have entered spring conditions, the avalanche hazard will fluctuate greatly depending on the strength of the overnight freeze and how quickly the snowpack is warmed up each day. Check out this guide to managing avalanche hazard during spring conditions HERE.In areas that remained more sheltered from the heat, like northerly aspects in the alpine, there may still be a dry snowpack with a well settled slab sitting on weak facets (sugary snow). Human triggering of persistent slabs on this layer may still be possible.Lower down in the snowpack, the base is composed of weak facets. Large deep persistent slab avalanches initiating on these facets is currently the primary concern for this region. They are most likely in rocky, alpine terrain where there is a shallow or highly variable snowpack depth. They would likely require a large trigger such as a cornice fall, snowmobile, or a group of people standing in the same spot.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.