Avalanche Forecast

Archived

Apr 17th, 2021–Apr 19th, 2021

Alpine

Natural and human triggered avalanches likely.

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.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon.

Rapidly rising temperatures will increase the likelihood for large cornice failures and wet loose avalanches. Start early and plan to be out of avalanche terrain before the heat of the day. Check out the Forecaster's Blog for more information on managing current conditions.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

SATURDAY NIGHT: Clear / Moderate, southeast ridgetop wind / alpine low temperature -3 / Freezing level 1700 m.

SUNDAY: Sunny / Moderate, southeast ridgetop wind / alpine high temperature 11 / Freezing level rapidly rising to 2900 m.

MONDAY: Sunny / Light, southeast ridgetop wind / alpine high temperature 11 / Freezing level 2700 m.

TUESDAY: Mix of sun and cloud / Light, southwest ridgetop wind / alpine high temperature 2 / Freezing level 1500 m.

Avalanche Summary

Several naturally triggered wet slab avalanches up to size 2.5 and numerous wet loose avalanches up to size 2 were reported on Thursday. See MIN.

Keep in mind that periods of rapid warming can weaken deeply buried weak layers and increase the likelihood of large natural avalanches.

Snowpack Summary

Lingering wind slabs may still be reactive in isolated areas on northerly aspects at upper elevations. All other terrain is undergoing a melt-freeze cycle with successive days of high freezing levels.

Strong solar radiation and warming often trigger wet loose avalanches and large cornice failures. Cornice falls could trigger large avalanches on deeply buried weak layers.

While there have not been many weak layers of concern this season, Keep in mind that periods of rapid warming can weaken deeply buried weak layers and increase the likelihood of large natural avalanches.This will more likely be an issue in shallow snowpack areas like the Wheaton compared to the thicker and stronger snowpack around White Pass.

Terrain and Travel

Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
Avoid travelling on slopes below cornices.
The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
Back off slopes as the surface becomes moist or wet with rising temperatures.
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.

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.