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Avalanche Forecast

Archived

Apr 9th, 2023–Apr 10th, 2023

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

Regions

Purcells, Dogtooth, East Purcell.

Prepare for a wet and stormy day. Observe your local conditions, and let that guide your terrain choice. Forecasted snow and rainfall amounts are uncertain.

Carefully choose the terrain you play in. A weak, unpredictable layer continues to lurk near the bottom of the snowpack.

Confidence

Low

Avalanche Summary

No notable avalanches were reported before 4 pm on Sunday. Expect avalanche activity to increase on Monday with the arrival of a wet storm.

On Saturday, near both Golden and Invermere. Several small (size 1-1.5), naturally triggered loose wet avalanches were reported on steep slopes. Sun and/or warm temperatures were the most likely triggers.

On Thursday, north of Golden, just outside of the forecast area, a large (size 2), rider triggered, deep persistent slab avalanche was reported on a northwest aspect in the alpine. The avalanche started 50 m above the riders, and 2 sympathetic avalanches were observed on the adjacent slope. See the excellent Mountain Information Network (MIN) post here for more information, including photos, and reflections on a close call.

Snowpack Summary

10-25 cm of new snow in the alpine covers settling, dry snow on shaded (northerly) aspects, and a frozen crust on solar aspects. At treeline, this new snow is likely to be denser, shallower, and moist.

Below treeline, 10-25 mm of rain starts to soak frozen crusts or already wet surfaces, and will be eating away at the snowpack at low elevations.

The mid-snowpack may still contain a number of weak layers, primarily in sheltered treeline terrain. No recent avalanche activity has occurred on these layers, but rising temperatures or an input of rain to the snowpack will test if these layers have strengthened.

The lower snowpack includes a widespread layer of large, weak facets and/or depth hoar crystals. This weak layer has been responsible for several very large and destructive avalanches throughout the season, including one on Thursday.

Weather Summary

Snow/Rain amounts for the incoming storm are uncertain. Weather models are not agreeing on how widespread or intense the precipitation will be. Prepare to continually evaluate the conditions, and change plans as necessary.

Sunday Night

Cloudy around Golden, partly cloudy around Invermere. 5-10 cm of snow expected in the alpine. Rain below 1800 m. Treeline temperature around 0°C. Light southwest ridgetop wind, trending to strong at higher elevations.

Monday

Cloudy. 5-15 cm of snow expected in the alpine. Snow/rain line drops to 1300 m further north, holds around 1900 m further south . Light southwest ridgetop wind, trending to moderate at high elevations.

Tuesday

Mostly cloudy. 5-12 cm of snow expected as the snow line drops back to valley bottom. Light southwest ridgetop wind, trending to moderate at high elevations. Moderate west ridgetop wind.

Wednesday

Partly cloudy. Possible trace of snow expected. Snow/rain line around 1000 m. Light northwest ridgetop wind.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Be careful to keep storm day fever from luring you out into bigger terrain features.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.