Avalanche Forecast

Issued: Apr 15th, 2018 4:38PM

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

jmcbride, Avalanche Canada

Cariboos.

It might be spring but it's still winter up high. Wind slabs are present at treeline and above, while loose, wet avalanches are a concern at lower elevations. Also be mindful of large cornices overhead, and avoid slopes below if it's warm or sunny.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Increasing cloud. Ridge wind light to moderate, southeast. Alpine temperature near -5. Freezing level 700 m.MONDAY: Cloudy, light flurries. Accumulation up to 2 cm. Ridge wind moderate to strong, southeast. Alpine temperature near -5. Freezing level 1700 m.TUESDAY: Mix of sun and cloud, light flurries. Accumulation up to 5 cm. Ridge wind light, northwest. Alpine temperature near -5. Freezing level 1600 m.WEDNESDAY: Mix of sun and cloud. Ridge wind light, southwest. Alpine temperature near -4. Freezing level 1800 m.

Avalanche Summary

Friday there was a report of a natural cornice collapse that produced a size 3 deep, persistent slab avalanche that failed on an early-season layer (300 cm deep) on a northeast aspect at 2600 m. Several loose, wet releases up to size 2.5, running to ground in low elevation paths were also reported on Friday.Wednesday there was a report of natural cornice failure that resulted in a size 2.5 wind slab release on a northeast aspect at 2700 m, while a skier was able to trigger a size 2 wind slab (40 cm deep and 100 m wide) on a recently buried crust on a similar aspect at 2400 m. On Tuesday a natural size 2.5 cornice failure was reported on a north facing alpine feature. A natural size 2.5 wind slab was also observed on a cross-loaded east facing feature at 2400 m.Last Monday, steep solar aspects produced natural loose wet avalanches to size 2 between 2000 and 2600 m, and a size 3 natural cornice failure was also reported from a north facing slope at 2600 m.

Snowpack Summary

About 10-20 cm of new snow covers a supportive crust on all aspects to at least 2100 m (and possibly higher on south aspects), while 30-60 cm of storm snow can be found at higher elevations. There are now a few different crusts in the upper snowpack, with only the upper, most-recently buried crust posing a concern with the recent storm snow.There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 100 to 150 cm below the surface. This buried crust/surface hoar interface was widely but has not produced any avalanche activity in the past week. It 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 a cornice collapse).Deeper persistent weak layers from December and January may be starting to become reactive to very large triggers. A recent cornice collapse is believe to have initiated a slab release on an early season layer, 300 cm deep.

Problems

Wind Slabs

Recent snow and wind have formed touchy wind slabs in leeward areas in the alpine and exposed features at treeline. These slabs may still be reactive to human triggers especially in areas where they sit on a recent crust.

Sluffs may be easy to trigger in steep terrain that is sheltered from the windUse caution in lee areas in the alpine and treeline. Storm snow has formed touchy slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Cornices

Several large cornice failures have been reported in recent days. A cornice collapse may have the potential to trigger a deep weak layer near the base of the snowpack resulting in a very large avalanche.

Give cornices a wide berth when traveling on ridges.Cornices may weaken with sun and daytime heating. Minimize your exposure to large cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3.5

Loose Wet

Daytime warming, rain, or a bit of sun may destabilize surface snow, initiating loose wet avalanche activity especially below treeline and on steep south facing features.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.If triggered, loose wet sluffs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2.5

Valid until: Apr 16th, 2018 2:00PM