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Avalanche Forecast

Archived

Apr 23rd, 2019–Apr 24th, 2019

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

Regions

Purcells.

Wind slabs may react to human triggers around ridges and lee features. Loose wet avalanches remain a concern, especially on sunny slopes.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TUESDAY NIGHT: Cloudy with clear periods with isolated flurries, trace to 5 cm, light to moderate west wind, alpine temperature +2 C, freezing level 1300 m.

WEDNESDAY: Mix of sun and clouds, moderate northwest wind wind, alpine temperature +1 C, freezing level 1800 m.

THURSDAY: Cloudy with sunny periods, light west wind wind, alpine temperature -1 C, freezing level 2100 m.

FRIDAY: Mix of sun and clouds, light west wind, alpine temperature 0 C, freezing level 2200 m.

Avalanche Summary

On Saturday morning evidence of large (up to size 3) natural wind slab avalanche cycle was observed on all aspects above 1500 m; natural avalanches continued throughout the day, two large (2.5-3) natural wind slab avalanches were observed around 3 pm on south aspects. Storm and wind slab avalanches to size 3 were triggered with explosives on all aspects in the alpine (above 2300 m). Impressive results were recorded including sympathetic avalanches to size 2.5; one shot triggered 6 large avalanches as far as 600 m away.

Avalanche activity continued through Sunday, natural wind slab avalanches to size 3 were observed with daytime warming and explosives triggered several size 2 wind slab avalanches on north and east aspects at 2500 m. No avalanche observations were reported on Monday.

Snowpack Summary

Rain has soaked the snowpack at treeline and below. In the alpine, the recent snow is settling and preserved on north aspects. A crust is present on all solar alpine aspects and below 2200 m, the strength of which will depend on overnight recovery and the speed at which the snowpack warms during the day.

Weak and sugary faceted grains may remain at the bottom of the snowpack in the alpine, producing a low likelihood but high consequence scenario. Steep, rocky areas with a shallow snowpack are the most likely places to trigger this layer. At lower elevations the snowpack is below threshold and the bike trails are quickly drying.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.