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Avalanche Forecast

Archived

Mar 30th, 2023–Mar 31st, 2023

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

A weak snowpack still exists throughout the Purcells. Avoid thin and rocky start zones.

The best riding conditions can be found at higher elevations on shaded slopes where weak layers may be preserved. Minimize your exposure to large, high consequence slopes.

Confidence

Moderate

Avalanche Summary

Over the last three days wet loose avalanches have occurred primarily on steep south facing (sun affected slopes) at lower elevations with rising freezing levels and strong sunshine. Cloud and cooler temperatures on Friday will reduce the likelihood of wet avalanche activity.

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

Dry snow still exists at upper elevations on shaded slopes, where southwest winds may redistribute snow into small pockets of wind slab on north and east facing terrain. Faceted snow and surface hoar (up to 10 mm) may sit below in shaded and sheltered areas. Moist snow is present on most other aspects and elevations, sitting over a crust from previous melt freeze cycles.

In the middle of the snowpack there are lingering persistent weak layers, including layers of surface hoar in wind-sheltered terrain and a sun crusts on south aspects. Activity on these layers has tapered off, but triggering remains possible 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 and will continue to be a concern for the rest of the season.

Weather Summary

Thursday Night

Freezing levels drop back to 500 m, with light westerly winds around 10 km/hr. Partly cloudy skies.

Friday

Mostly cloudy with flurries delivering up to 5 cm of snow. Light southerly wind gusting 40 km/h. Freezing level rises to 1500 m, alpine temperatures of -5 °C.

Light snowfall continues overnight, around 5 cm.

Saturday

Cloudy with sunny periods possible in the afternoon. Light snowfall brings 5-10 cm. Light southwesterly wind gusting 40 km/h. Freezing level rises to 1500 m, alpine highs of -5 °C.

Sunday

A mix of sun and cloud with flurries delivering up to 5 cm. Freezing levels rise to 1300 m with alpine highs of -7 °C. Light southwest winds.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Be alert to conditions that change with aspect and elevation.
  • 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.

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.