Avalanche Forecast

Issued: Apr 10th, 2018 5:27PM

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

ghelgeson, Avalanche Canada

Purcells.

Watch for wind slabs immediately lee of ridge crest, pay attention to cornices and remember that we're still dealing with a persistent slab problem. Choose well-supported lines and travel early to take advantage of the overnight re-freeze.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Wednesday

Weather Forecast

Temperatures are expected to be slightly cooler Wednesday as we move into a pattern across the province that remains quite "winter-like." WEDNESDAY: Scattered cloud cover with potential for some clearing in the afternoon, freezing level beginning around 1400 m rising to about 1900 m, light west/southwest wind, 1 to 4 mm of precipitation possible. THURSDAY: Broken cloud cover, freezing level beginning around 700 m rising to about 1600 m, light south/southwest wind, 1 to 3 mm of precipitation possible.FRIDAY: A few clouds, freezing level beginning around 500 m rising to about 2000 m, light west/southwest wind, no significant precipitation expected.

Avalanche Summary

On Monday intense wind loading produced wind slab avalanches to size 2 on north facing terrain around 2400 m. Solar radiation (direct sun) also produced natural storm slab and loose wet avalanches to size 2.5 on on a variety of aspects between 1700 and 2600 m. We received the following information second hand, and all the details may not be accurate, if you have additional information, we would love to hear from you. On Sunday six riders were involved in an avalanche up Doctor Creek. One was stuck, the second went to help and also got stuck, the third rode up the slope to help and triggered an avalanche that buried the three, "up to their faces." The riders credit airbag packs with saving their lives and although one sled was wrecked, the group was able to extricate themselves. The slope was reportedly north facing and failed as a wet slab.

Snowpack Summary

Recent wind and cold snow have formed wind slabs 10 to 50 cm in depth in the alpine that sit on a mix of crusts and surface hoar. Test profiles show resistent planar failures at this interface. In wind sheltered terrain Saturday's new snow rests on a surface crust that exists on all aspects aside from true north below 2000 m. This crust extends up to around 2400 m on south facing slopes. The mid-March Persistent Weak Layer (PWL) is now 40 to 90 cm below the surface. This layer is composed of a crust on all aspects at low elevations. At upper elevations the layer presents as a crust on solar aspects (south and west) and buried surface hoar on polar aspects (north and east). The likelihood of triggering a deeper persistent slab avalanche is steadily decreasing but the consequence of doing so remains high. Persistent slab avalanche activity on polar (north and east) aspects has dramatically decreased and solar (south and west) aspects are expected to be the most suspect over the next few days.Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.

Problems

Loose Wet

Warming temperatures and a bit of sun may destabilize the snow surface and initiate loose wet avalanche activity which will likely be most pronounced on steep south facing features. The likelihood of cornice failure also increases in the afternoon.

Large cornices become weak with daytime heating, avoid traveling on or underneath them.Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Use caution above cliffs and terrain traps where loose avalanches may have severe consequences.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

A buried persistent weak layer consisting of surface hoar and crust is now 40 to 90 cm below the surface and may remain sensitive to human triggering in the alpine, especially on steep solar aspects in the afternoon.

Pay attention to overhead hazards like cornices which could trigger persistent slabs.Be aware of the potential for large, deep avalanches due to deeply buried weak layers.Use caution on open slopes and convex rolls where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Wind Slabs

Wind slabs up to 50 cm in depth continue to be problematic immediately lee of ridge crest and may remain sensitive to human triggering on Wednesday.

Be especially careful with wind loaded pockets near ridge crests and roll-overs.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Apr 11th, 2018 2:00PM