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Avalanche Forecast

Apr 19th, 2018–Apr 20th, 2018
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: 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.

Confidence

Moderate -

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.

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.

Avalanche Problems

Loose Wet

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.
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.

Aspects: North, North East, East, South East, South.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Cornices

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.
Cornices become weak with daytime heating. Always take stock of overhead hazards.Give cornices a wide berth when travelling on or below ridges.

Aspects: North, North East, East, South East.

Elevations: Alpine.

Likelihood: Possible - Likely

Expected Size: 1.5 - 3

Wind Slabs

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.
Use extra caution around cross-loaded terrain features.Be especially careful around wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 1 - 2