Avalanche Forecast

Archived

Apr 26th, 2023–Apr 27th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Below Threshold.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Below Threshold.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Below Threshold.

Regions

Glacier.

Warm temperatures will produce large avalanches, avoid avalanche terrain in the heat of the day.

Confidence

Moderate

Avalanche Summary

Numerous moist/wet, loose surface avalanches have been observed from steep gullies/slopes on all aspects at and below treeline. These point releases gather substantial mass as they move downslope into warmer snow.

As the week continues to warm up, expect these wet/loose avalanches to increase in size and potentially step down to deep layers, possibly even the Nov 17 facets.

Snowpack Summary

5cm of new snow sits over a crust at upper treeline and alpine except for high north aspects. Below this are several buried crusts on solar aspects which may provide a failure plane for slab avalanches as temps rise dramatically today.

Below treeline the snowpack is moist and has been weakened by rain and warm temperatures.

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

Weather Summary

A strong ridge of high pressure is delivering very warm temperatures with high freezing levels and sunny skies.

Thurs: sun w/ cloudy periods, Alp high 2 °C, light west winds, FZL 2800m

Fri: sunny skies, Alp high 9°C, light west winds, FZL 3400m

Sat: mix of sun and cloud, Alp high 11°C, light southwest winds, FZL 3600m.

Terrain and Travel Advice

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.
The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.