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Avalanche Forecast

Archived

Mar 21st, 2019–Mar 22nd, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
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.

Regions

South Rockies.

The likelihood of human triggering large avalanches on deeply buried weak layers is keeping the hazard at HIGH on Friday. Travel in avalanche terrain is NOT recommended.

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Clear skies / Light, southeasterly winds / Alpine low 6 C / Freezing level 3100 m.FRIDAY: Sunny / Light, westerly winds / Alpine high 6 C / Freezing level 2900 m.SATURDAY: Mostly cloudy / Light, northeasterly winds / Alpine high 0 C / Freezing level 2400 m.SUNDAY: Snow/rain; 5-10 mm.  / Light, easterly winds / Alpine high -3 C / Freezing level 1700 m.

Avalanche Summary

On Wednesday, an explosive control mission produced an avalanche with every shot placed (nearly 20 in total). They were loose wet avalanches on sun-exposed slopes and dry, slab avalanches on northerly aspects, up to size 2.5. Additionally, large (size 2-2.5) loose wet natural avalanches continue to occur on solar aspects.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 metres. Further to this activity, any sun-exposed snow became isothermal (slushy and cohesionless), and huge whumpfs that collapsed the basal snowpack were triggered during ski touring. Check out their video HERE.Given the above activity, loose wet avalanches remain a daily concern in steep, sun-exposed terrain (and in runout zones) while concern is increasing for deep basal (bottom of the snowpack) weaknesses that have the potential to produce very large and destructive slab avalanches.

Snowpack Summary

Upper snowpack: Getting warm and moist during the day, likely forming weak crusts overnight that deteriorate during the day. On sunny aspects the upper snowpack has become increasingly isothermal (slushy and cohesionless) with successive days of warming. Mid pack: The mid-snowpack consists of facets (weak, sugary snow) and layers of harder wind effected snow. Recent loose wet avalanches have been entraining additional mass by gouging into this faceted snow. These facets have also acted as a failure plane in recent slab releases.Lower pack: The strength of the lower snowpack is increasingly in question in shallower areas where the February cold was able to weaken basal (bottom of the snowpack) layers and warm temperatures are increasing the strain on these weaknesses each day.  Many of the recent slab avalanches failed on these facets sitting just above the ground. It's a good time to stand aside and let the mountains shed their coat. Stability will improve greatly when temperatures cool off.

Problems

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.

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.