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Avalanche Forecast

Archived

Apr 1st, 2023–Apr 2nd, 2023

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

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Watch for small but reactive wind slabs as you gain elevation.

Small wind slabs may trigger larger avalanches on deeply buried weak layers. Continue to avoid wind affected, thin and rocky terrain.

Confidence

Moderate

Avalanche Summary

On Friday a size 3 naturally triggered avalanche was reported in the Dogtooth Range. While the failure plane is unknown the report mentions impressive propagation, likely on a buried persistent weak layer.

On Thursday a natural cornice fall (from strong sunshine) triggered a loose dry avalanche to size 2. Several naturally triggered ice falls have also been reported this week - while they have not triggered avalanches they are hazardous on their own.

No activity on the deeply buried weak layers has been reported this week. However thin and rocky terrain features in the upper treeline and alpine should still be avoided.

Snowpack Summary

New snow and wind are forming wind slabs at higher elevations, over a melt freeze crust (on all aspects at low elevations, and on sun affected slopes to mountain top). On north facing slopes at treeline and alpine, new snow sits over previously wind affected surfaces. Surface hoar may exist below the recent snow, in wind sheltered and shaded terrain - increasing reactivity.

The mid snowpack holds several persistent weak layers that vary throughout the Purcells, including layers of surface hoar in wind-sheltered terrain and sun crusts on south facing slopes. No recent activity has occurred on these layers, but they may remain triggerable in isolated features.

The lower snowpack includes a widespread layer of large, weak facets and or depth hoar crystals. This weak layer has been responsible for a number of very large, destructive avalanches this season, including several last week during warm temperatures and will continue to be a concern for the rest of the season.

Weather Summary

Saturday Night

Cloudy. Light snowfall brings up to 5 cm. Moderate southwesterly wind gusting strong. Freezing level drops to valley bottom.

Sunday

Mostly cloudy with flurries with trace accumulations. Freezing levels rise to 1300 m with alpine highs of -7 °C. Light west winds.

Monday

Partly cloudy. Light easterly winds. Freezing levels rise around 1300 m.

Tuesday

Clearing skies with 1300 m freezing levels. Light easterly winds.

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.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.