Avalanche Forecast

Archived

Apr 25th, 2023–Apr 26th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Below Threshold.

Regions

Glacier.

Rain up to Treeline elevations is forecasted for Rogers Pass. With its arrival expect avalanches to increase in size/frequency throughout the park.

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

At Treeline elevations and below, rain and clouds are preventing a strong surface crust recovery.

In the high Alpine, true N'ly aspects hold dry snow. On solar aspects, a breakable crust overlies a series of buried crusts, which may provide a failure plane for slab avalanches as temps rise.

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

Weather Summary

A warm, wet Wed, then clearing and much warmer conditions arriving for the weekend.

Tonight: cloud/clear periods, Alp low -2*C, gusty mod/strong SW winds, 1800m FZL

Wed: Rain, flurries (10cm) above 2200m, Alp high 2*C, strong SW winds

Thurs: sun and cloud, Alp high 2*C, light/mod W winds, 2400m FZL

Fri: sun, Alp high 8*C, 3600m FZL

Terrain and Travel Advice

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.
Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.

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.