Avalanche Forecast

Archived

Apr 14th, 2021–Apr 16th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

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 unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon.

Expect a spike in avalanche activity on Friday with rapidly warming temperatures (read more in this Forecasters' Blog). Wind slabs may also remain reactive to human triggering.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

WEDNESDAY NIGHT: Partial clearing overnight, south wind 40-60 km/h easing to 30 km/h, treeline temperatures drop to -5 C.

THURSDAY: Partly cloudy, 20 km/h south wind, freezing level climbing to 1500 m in the afternoon.

FRIDAY: Mix of sun and cloud, light south wind, freezing level climbing from 1500 to 2200 m.

SATURDAY: Mix of sun and cloud with some isolated flurries, light northeast wind, freezing level around 1500 m.

Avalanche Summary

With the incoming warming trend expect avalanche activity to transition from wind slab to wet loose activity. Weather forecasts suggest the greatest warming impacts will be on Friday. Keep in mind periods of rapid warming can increase the likelihood of large natural avalanches.

There were a few reports of small wet loose avalanches at low elevations on Tuesday and numerous reports of reactive wind slab avalanches between Friday and Monday (with multiple size 1-2 avalanches running on a 30-70 cm deep crust layer).

Snowpack Summary

Warming temperatures over the next few days will form moist surfaces at lower elevations and on sun-exposed slopes (if the clouds break up). 15-30 cm of wind-affected snow overlies a hard crust found up to 1300 m. The wind effect is particularly widespread along the highway corridor at White Pass but may be less so as you push into the side valleys.

While there have not been many weak layers of concern this season, there is some uncertainty about whether the big warm up on Friday will increase the reactivity of any deeper layers. 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

Extra caution for areas experiencing rapidly warming temperatures for the first time.
Back off slopes as the surface becomes moist or wet with rising temperatures.
Be aware of the potential for large avalanches due to the presence of a buried crust.
Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.