Avalanche Forecast

Archived

Apr 20th, 2021–Apr 21st, 2021

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 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

Lizard-Flathead.

One more day of warm sunny weather before the next snowfall arrives. Avoid sun-exposed slopes and cornices at peak midday warming on Wednesday.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

Tuesday night: Clear, light winds becoming west, alpine temperature -4 C, freezing level dropping to valley bottom.

Wednesday: Sunny, light northwest winds, alpine high temperature -1 C, freezing level 2600 m.

Thursday: Cloudy, 10-20 cm of snow, light northeast wind with moderate ridgetop gusts, alpine high temperature near 0 C and dropping through the day, freezing level dropping to valley bottom.

Friday: Mainly cloudy, light wind becoming southwest, alpine high temperature -3 C, freezing level rising to 1800 m.

Avalanche Summary

Over the past several days with sunny weather, there have been reports of natural wet loose avalanches ranging from size 1-2.5.

Snowpack Summary

Sunny weather is forecast to stick around for Wednesday, which may initiate wet loose avalanches as the snow loses cohesion. Cornices are large and looming along ridgelines. Sun and warm temperatures will increase the chances of cornice failures, which could trigger avalanches on the slopes below. Check out the Forecaster's Blog for information on how to manage these spring conditions.

The snowpack is overall strong and settled in most areas. However, steep and rocky alpine slopes with a shallow or thin to thick snowpack may still harbor deeply buried weak layers. Glide cracks releasing as full depth glide slab avalanches become more common in the spring and are extremely difficult to predict. Best practice is to avoid slopes with glide cracks.

The snow line is slowly creeping up the mountains, making some access areas snow-free.

Terrain and Travel

Extra caution is needed around cornices under the current conditions.
Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
Stay off recently wind loaded slopes until they have had a chance to stabilize.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.