Avalanche Forecast

Issued: Apr 9th, 2017 4:43PM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Wind Slabs, Cornices and Persistent Slabs.

cgarritty, Avalanche Canada

Purcells.

The new snow is on a steady stabilizing trend, but avalanche hazards will persist the longest in wind affected areas. Watch for solar exposure to rapidly undermine stability.

Summary

Confidence

Moderate -

Weather Forecast

Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Tuesday: A mix of sun and cloud. LIght southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Wednesday: Mainly cloudy with flurries beginning in the afternoon. Light to moderate east winds. Freezing level to 1900 metres with alpine temperatures of -2.

Avalanche Summary

Saturday's reports showed several storm slabs releasing to Size 3 on various aspects in the Bugaboo Range, an area where up to 40 cm of new snow accumulated over the past few days. Ski cutting and explosives control in the Golden area yielded several Size 1-1.5 loose dry avalanches.Reports from Friday included observations of Size 1 wind slabs releasing with ski cutting in the Golden area. One report from the central Purcells detailed evidence of a natural avalanche cycle to Size 2 in steep terrain as a result of new snow and warm temperatures. Loose wet avalanches were observed running to Size 1 in steeper terrain below 1900 metres.

Snowpack Summary

Recent moderate to strong winds have redistributed new snow into wind slabs on a range of aspects at higher elevations. Fragile new cornice growth also occurred along ridgelines over the course of the week. The new snow has buried melt-freeze crusts on all aspects below about 2200 metres and in the high alpine on solar aspects. Isolated surface hoar may be found below the new snow on shaded aspects at high elevations. Below the new snow interface, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. At higher elevations, the February crust/facet layer is now down around 130-150 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases were also reported in late March and early April, keeping these layers an ongoing concern.

Problems

Wind Slabs

Recent moderate to strong winds shifted between a variety of directions and wind slabs now exist on a wide range of aspects. Slabs may be more reactive where they lie above recently formed crusts or more isolated surface hoar.

Keep an eye out for reverse loading created by shifting winds.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Cornices have grown large and may break off naturally due to solar exposure or daytime warming. Cornice falls were responsible for triggering a number of large persistent slab avalanches last week.

Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Avoid travel on slopes that are exposed to cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3

Persistent Slabs

A cornice fall or smaller slab avalanche currently has the potential to trigger large, destructive avalanches on deeply buried weak layers. This is more likely to occur in thin or variable snowpack areas at higher elevations.

If triggered, wind slabs or cornices may step down to deeper layers and result in large avalanches.Recognize and avoid avalanche runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Apr 10th, 2017 2:00PM