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Avalanche Forecast

Archived

Apr 15th, 2021–Apr 16th, 2021

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

Little Yoho.

The crux of the big warmup approaches. We expect a good overnight freeze for Friday, but no freeze for Saturday morning. Be clear of all avalanche terrain by noon and do something else if the snow is not frozen. Saturday might be too warm and slushy.

Weather Forecast

The clear skies and warm, sunny weather will continue until Sunday, getting slightly warmer each day. Freezing levels are forecast to reach 3000 m on Friday and a poor freeze is expected on Friday overnight. Saturday could be "the day" for avalanches. The next few days is the biggest warmup to 3000 m so far this year.

Snowpack Summary

Hard surface crusts in the morning, then wet snow in the afternoon. High elevation north aspects will still hold dry snow. Another solid overnight freeze is expected for Friday morning, then deteriorating rapidly as the day warms up. There are several persistent layers n the mid to lower snowpack will wake up over the next 48 hr.

Avalanche Summary

Many loose snow avalanches up to size 2 were observed from the valley bottom on Thursday, running long distances in gullies. We had no observations after 2:00 pm, and expect the peak of avalanche activity to be later in the afternoon, so these observations are likely incomplete.

Confidence

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.

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.