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Avalanche Forecast

Archived

Mar 31st, 2023–Apr 1st, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
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 wind slabs forming at higher elevations.

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 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

Light accumulations of storm snow will form deeper deposits on north and east facing slopes at treeline and above. New snow will sit over previous wind affected surfaces at higher elevations on shaded aspects, faceted snow and surface hoar in sheltered areas, and over a melt freeze crust on south facing slopes and at low elevations.

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. Activity on these layers has tapered off, however a layer of surface hoar around Toby Creek buried up to 70 cm has produced recent test results indicating it is still reactive.

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

Friday Night

Mostly cloudy with flurries delivering up to 5 cm of snow. Moderate southwest wind gusting 50 km/h. Freezing level remains around 500 m overnight.

Saturday

Cloudy with sunny periods possible in the afternoon. Light snowfall brings 5-10 cm for eastern terrain. Western Purcells may see up to 25 cm total. Moderate southwesterly wind gusting 50 km/h. Freezing level rises to 1500 m, alpine highs of -5 °C.

Sunday

A mix of sun and cloud with flurries with trace accumulations. Freezing levels rise to 1300 m with alpine highs of -7 °C. Light west winds.

Monday

Mostly cloudy. Light westerly winds. Freezing levels rise around 1000 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.
  • 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

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.

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.