Avalanche Forecast
Purcells
Clues to mountain hazards are currently quite apparent on the surface. Tune in to overhead hazards, moist snow, and lingering wind slabs as you travel and watch for the destabilizing effect of sun exposure.
Avalanche Problem 1: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
- Manage your sluff and be extra cautious where long slopes allow for more snow entrainment.
- Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.
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 Friday. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.
Travel and Terrain Advice
- Cornices become weak with daytime heating. Always take stock of overhead hazards.
- Give cornices a wide berth when travelling on or below ridges.
Avalanche Problem 3: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Lingering wind slabs formed after the last snowfall my still be reactive to human triggering in isolated areas. The main concern is for steep wind-loaded slopes near ridge crests.
Travel and Terrain Advice
- Use extra caution around cross-loaded terrain features.
- Be especially careful around wind loaded pockets near ridge crests and roll-overs.
Avalanche Summary
Reports from from Wednesday included an observation of a natural size 3 slab release 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. Elsewhere in the north of the region, explosives control yielded several wind slabs, storm slab, and cornice releases, generally to size 2, with a couple of size 2.5. One size 3 deep persistent slab was also reported.
Reports from Tuesday included several observations of large (size 2) natural storm slab releases focused around steep features 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, continued warm temperatures will be maintaining 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 of rapidly settling 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. Within this storm snow there are several buried crusts with the mostly recently buried (down about 20 cm) becoming a diminishing concern as warm temperatures promote settlement and bonding in the upper snowpack.
With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains 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 should be kept in the back of our minds for its capability to produce large avalanches should it be triggered with a heavy load, such as a cornice collapse.
Deeper persistent weak layers from December and January are considered dormant at this time.
Weather Forecast
Friday: A mix of sun and cloud with isolated wet flurries, cooling and increasing overnight. Light southwest winds. Freezing level to 2300 metres with alpine high temperatures around 0.
Saturday: Cloudy with continuing flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds. Freezing level to 1800 metres with alpine high temperatures around -2.
Sunday: A mix of sun and cloud. Light west winds. Freezing level to 1900 metres with alpine high temperatures around -2.
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Sustained warm temperatures are expected to maintain elevated chances of loose wet avalanches in steeper terrain - especially on sun-exposed slopes. Loose snow releases may occur naturally or with a human trigger.