Avalanche Forecast
Purcells
Forecast sunshine and warming will increase the likelihood of triggering in a wide range of avalanche problems on Thursday. Expect stability to deteriorate over the day.
Avalanche Problem 1: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.
- Manage your sluff and be extra cautious where long slopes allow for more snow entrainment.
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
Avalanche Problem 2: Cornices
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Large cornice failures have been reported in the past week and cornices will weaken with forecast sun exposure on Thursday. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.
Travel and Terrain Advice
- Give cornices a wide berth when travelling on or below ridges.
- Cornices become weak with daytime heating. Always take stock of overhead hazards.
Avalanche Problem 3: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
The strength of storm and wind slabs formed after the last snowfall will be tested by sunshine and warming on Thursday. The greatest caution is needed around steep or wind-loaded slopes as well as sun-exposed aspects where slabs formed over a crust.
Travel and Terrain Advice
- Be especially careful around wind loaded pockets near ridge crests and roll-overs.
- Use extra caution around cross-loaded terrain features.
Avalanche Summary
An early observation from Wednesday detailed a natural size 3 slab avalanche that is believed to have released over a persistent weak layer, potentially from mid-March. Evidence of the release was seen from a distance in the Dogtooth range.
Reports from Tuesday included several observations of large (size 2) natural storm slab releases focused around steep features just below ridgetop.
Poor visibility limited observations of avalanche activity on Monday.
On Sunday there was a report of a near miss for skiers who triggered a size 2 wind slab on a north aspect at treeline in the northern part of the region. The northwestern part of the region saw a warming-induced natural avalanche cycle up to size 3 on large alpine features in the recent storm snow.
Looking forward, a trend toward clearing skies and warming temperatures will be increasing chances of loose wet avalanche activity as well as testing the strength of storm slabs and wind slabs formed in the wake of recent snowfall and wind events.
Snowpack Summary
Generally 30-40 cm on recent storm snow overlies a crust on all aspects to at least 2000 m (and possibly higher on south-facing slopes), with up to 80 cm observed in some areas in the northwest of the region. Recent shifting strong winds pressed and redistributed the most recent accumulations into new wind slabs on a range of aspects. Below 2200 m the new snow has a thin surface crust that breaks down to moist or wet snow in the afternoons.
Within the upper snowpack there are now several buried crusts with the mostly recently buried (down about 20 cm) posing a concern as the uppermost layer of storm snow settles and bonds to it.
There is some lingering concern around the mid-March persistent weak layer in the alpine where it is found 60 to 100 cm below the surface. This buried crust/surface hoar interface is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think step-down from a surface avalanche or cornice collapse)
Deeper persistent weak layers from December and January are considered dormant at this time.
Weather Forecast
Thursday: Mainly sunny. Light southeast winds shifting southwest. Freezing level to 2200 metres with alpine high temperatures around 0. Weak overnight cooling.
Friday: Mainly cloudy with light flurries beginning in the afternoon and increasing overnight. Light southwest winds. Freezing level to 2300 metres with alpine high temperatures around 0 to +1.
Saturday: Cloudy with continuing flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds shifting to west. Freezing level to 1800 metres with alpine high temperatures around -3.
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Rising freezing levels and increasing sunshine will destabilize surface snow and promote loose wet avalanches in steeper terrain - especially on sun-exposed slopes. Loose snow releases may occur naturally or with a human trigger.