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Avalanche Forecast

Archived

Apr 25th, 2023–Apr 26th, 2023

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 unlikely, human triggered possible.
Below Treeline
Below Threshold.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Below Threshold.

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

Forecast 10-15 cm of snow and moderate southerly wind may form reactive wind slabs on lee features in specific locations.

Concern for triggering very large deep persistent slab avalanches in the Haines Pass area remains. Avoid steep, rocky, and wind-affected areas where triggering slabs are more likely.

Confidence

Low

Avalanche Summary

No avalanches were reported on Monday. However, observations in this region are currently very limited.

Observations are limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.

Snowpack Summary

Forecast 10-15 cm of snow and moderate southerly wind may form reactive wind slabs on lee features in specific locations.

Cornices are very large and loom over slopes below like gargoyles. Cornice falls may trigger large avalanches on the slopes below.

A robust crust exists on all aspects up to approximately 1400 m and to ridgetop on sunny aspects.

A weak layer of surface hoar/crust/facets buried in early January is now around 100 cm down in most areas. A significant warming event or a large trigger (like a falling cornice) are the most likely things to activate this layer.

Weather Summary

Tuesday Night

Cloudy with isolated flurries; 0-5 cm / 40 km/h southeast ridgetop wind / Temperature at treeline around -5 C / Freezing level valley bottom

Wednesday

Cloudy with flurries; 5-15 cm / 35 km/h south ridgetop wind / Temperature at treeline around 1 C / Freezing level 1100 m

Thursday

Mostly cloudy with isolated flurries; 5-10 cm / 60 km/h south ridgetop wind / Temperature at treeline around 1 C / Freezing level 1100 m

Friday

Cloudy / 30 km/h south ridgetop wind / Temperature at treeline around 2 C / Freezing level 1300 m

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Cornice failure may trigger large avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.

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.