Avalanche Forecast

Issued: Mar 24th, 2019 5:05PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Loose Wet and Deep Persistent Slabs.

jsmith, Avalanche Canada

South Rockies.

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

Summary

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

This problem is more likely at lower elevations where there was a weak or no overnight re-freeze. Sunshine and air temperatures above 0 C can rapidly increase the likelihood of triggering loose wet avalanches.

Avoid terrain traps such as cliffs and gullies that increase the consequence of small avalanches.Avoid sun exposed slopes when the solar radiation is strong, especially if the snow is moist or wet.Cornices become weak with daytime heating, travel early on exposed slopes.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

Human triggering of large deep persistent slab avalanches remains possible; especially in rocky, alpine terrain with a shallow or highly variable snowpack depth.

Pay attention to changing conditions with elevation and/or aspect.Avoid re-grouping in rocky areas with a shallow snowpack, remote triggering is still possible.Avoid steep, rocky terrain in the alpine where there is a shallow or highly variable snowpack depth

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Mar 25th, 2019 2:00PM