Avalanche Forecast

Archived

Apr 9th, 2021–Apr 10th, 2021

Alpine

Natural avalanches possible, human triggered probable.

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, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Lizard-Flathead.

New snow and wind are expected to increase the avalanche danger at upper elevations. Watch for areas of wind-drifted snow, especially near ridge-crests, roll-overs, and in steep terrain, and minimize your exposure to cornices.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Friday night: Cloudy, 5-10 cm of snow, moderate southwest wind with strong gusts at ridgetops, treeline temperatures near -6 C, freezing level dropping to 1200 m.

Saturday: Cloudy, 5-10 cm of snow, light southwest wind, treeline temperatures near -5 C, freezing level rising to 1400 m and dropping to valley bottom overnight.

Sunday: Sunny with afternoon cloud, light variable wind, treeline temperatures near -2 C, freezing level rising to 1700 m and dropping to valley bottom overnight.

Monday: Mix of sun and cloud, light northeast wind, treeline temperatures near -4 C, freezing level rising to 1500 m and dropping to valley bottom overnight.

Avalanche Summary

On Thursday, there were reports of several small (up to size 1.5) loose dry avalanches.

Snowpack Summary

Another 10-20 cm of new snow is forecast to accumulate by midday Saturday with moderate southwest wind. The new snow will combine with the previous 10-20 cm of snow from earlier in the week, continuing to build fresh wind slabs in lee features that may be possible to human trigger. Cornices are large, looming, and capable of triggering avalanches when they fail.

The mid-pack is firm and well settled. Some faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack. Snow line is slowly creeping up the mountains to roughly 1400 m in elevation. Check out this MIN report for more details on the access from common staging areas.

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.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avoid freshly wind loaded terrain features.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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.

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.