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Avalanche Forecast

Archived

Apr 18th, 2024–Apr 19th, 2024

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

Regions

Haines Pass.

Hunting dry snow on high north aspects puts you in the same terrain where it's possible to trigger a destructive slab. Manage the problem by choosing simple terrain free from overhead hazard.

Confidence

Moderate

Avalanche Summary

Riders saw evidence of recent large persistent slab avalanches and we received many reports of whumpfing (e.g., here). The avalanche observations add to the many natural and rider-triggered avalanches that released a week ago in alpine terrain. These weak layers may take some time to strengthen, meaning they may remain active to the weight of a person or machine for the foreseeable future.

Please consider sharing your observations to the Mountain Information Network.

Snowpack Summary

Recent strong wind has produced wind-affected snow in the alpine. Soft, settled snow may still be found in wind-sheltered terrain in the alpine. The snow surface on sun-exposed slopes will become moist or wet during the day and freeze into a hard melt-freeze crust overnight.

Weak layers of surface hoar crystals and/or faceted grains may be found around 30 to 70 cm deep in the snowpack. These problematic layers may be associated with a hard melt-freeze crust above or below. These layers were the culprit of many large avalanches last week and remain unstable in snowpack tests.

Cornices are large and looming at this time of year.

Weather Summary

Thursday night

Clear skies. 20 to 30 km/h southeast ridgetop wind. Above 0 °C temperatures at ridgetop with an above freezing layer forming between 1500 - 2400 m.

Friday

Clear skies with possible valley cloud below 1500 m. 20 to 30 km/h southeast ridgetop wind. Treeline temperature 2 °C with an above freezing layer persisting between 1500 - 2000 m.

Saturday

Becoming mostly cloudy. 10 - 20 km/h east ridgetop wind, easing. Treeline temperature +1 °C. Above freezing layer dissipated with freezing level to 1500 m in the afternoon.

Sunday

Cloudy with continuing scattered flurries from overnight bringing less than 3 total cm of new snow. 10-15 km/h south ridgetop wind, increasing. Treeline temperature around 0 °C with freezing level to 1300 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Choose conservative terrain and watch for clues of instability.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Cornice failures could trigger very large and destructive avalanches.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.

Problems

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.

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.