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Avalanche Forecast

Archived

Apr 24th, 2019–Apr 25th, 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.

A wintery snowpack still exists at upper elevations. Lingering wind slabs may still be reactive to human triggers.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY: Cloudy with sunny periods, alpine temperatures near -2 and freezing levels 2000 m. Ridgetop winds light from the southwest

FRIDAY: Mix of sun and cloud with some flurries. Alpine temperatures near -3 and freezing levels 2000 m. Ridgetop wind moderate from the northwest.

SATURDAY: Snow amounts 5-10 cm. Alpine temperatures near -6 and freezing levels 1600 m. Ridgetop wind moderate to strong from the northwest.

Avalanche Summary

On Wednesday, no new avalanches were reported. The avalanche hazard may increase when the sun comes out, especially on solar aspects in the afternoon. Last Saturday morning evidence of large (up to size 3) natural 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.

Snowpack Summary

A supportive surface crust caps a mostly isothermal snowpack at lower elevations. In the alpine, the recent snow is likely settling and preserved as cold, wintery snow on north aspects where reactive wind slabs may still linger. A crust is present on all solar alpine aspects and below 2200 m. The strength of the crust will depend on overnight recovery and the speed at which the snowpack warms up 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.

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.