Avalanche Forecast

Archived

May 5th, 2023–May 7th, 2023

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Glacier.

With no overnight refreeze this week, the entire snowpack is isothermal in most locations and will loose cohesion quickly with daytime warming or rainfall.

Large destructive natural avalanches remain possible. If air temps are warm or it is raining, travel in avalanche terrain is not recommended.

Confidence

High

Avalanche Summary

Natural activity was ongoing on Friday, with several large wet loose avalanches observed in the highway corridor.

This is capping off a very active week of spring avalanche activity - there was a widespread cycle of natural and controlled, wet loose and deep slab avalanches with numerous sz 3, and isolated sz 4's. Many avalanche paths failed down to ground once the avalanches were in motion.

Snowpack Summary

Warm temps have penetrated the snowpack creating a moist, isothermal snowpack on all aspects into the alpine. Buried crusts in the upper 50 cm are breaking down. Shallow snowpack features have loose, weak snow to ground.

20-40cm above the ground the Nov 17 basal weakness can still be found in many areas.

Weather Summary

Warm and dry weather will come to an end Friday, as a trough of low pressure brings light precip and dropping freezing levels (FZL).

Tonight: Cloudy periods, Alpine Low 3°C, FZL 2500m, Moderate E ridgetop wind.

Sat: Isolated showers/wet flurries, High 5°C, FZL 2600m, light S winds.

Sun: Scattered flurries (4cm), Low -1°C, High 1°C. FZL 2200m.

Mon: Isolated flurries, Low -1°C, High 5°C, FZL 2600m.

Terrain and Travel Advice

Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.

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.

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.