Avalanche Forecast

Issued: Apr 17th, 2018 4:45PM

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

cgarritty, Avalanche Canada

Cariboos.

Sunshine and warming are set to maintain heightened avalanche danger over the coming days. Expect stability to deteriorate as each day progresses.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Freezing level rising to 1700 metres with alpine high temperatures around -6.Thursday: Mainly cloudy. Light to moderate south winds. Freezing level rising to 1900 metres with alpine high temperatures around -3. Weak overnight cooling.Friday: Cloudy with flurries beginning in the evening and continuing overnight. Moderate south winds. Freezing level to 1900 metres with alpine high temperatures around -2.

Avalanche Summary

On Sunday there was a report of a natural, cornice-triggered size 2.5 persistent slab avalanche on a west aspect at 2350 m that is believed to have failed on the mid-March layer.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. Last Tuesday, another natural size 2.5 cornice failure was reported on a north facing alpine feature.

Snowpack Summary

About 30 cm of recent snow covers a supportive crust on all aspects to at least 2100 m (and possibly higher on south aspects), while 40-60 cm of storm snow can be found at higher elevations. Below 2200 m this new snow has a surface crust becoming moist or wet by the afternoon.Within the upper snowpack there are now several different crusts with only the shallowest of these remaining a concern as the uppermost layer of storm snow settles and bonds to it.There is some lingering concern around the mid-March persistent weak Layer in the alpine where it is found 100 to 150 cm below the surface. This buried crust/surface hoar interface is still capable of producing large avalanches if it is 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

Loose Wet

Rising freezing levels and increasing sunshine are likely to destabilize surface snow and promote loose wet avalanches in steep terrain. 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.Use extra caution on slopes if the snow is moist or wet.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Storm Slabs

Storm slabs formed after the last round of snowfall may remain reactive to human triggering on Tuesday. The greatest caution is needed around steep or convex terrain as well as sun-affected slopes where slabs formed over a recent crust.

Exercise increased caution around south aspects where new snow may have formed a slab over crust.Watch for signs of instability such as shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Several large cornice failures have been reported in recent days. Large cornice collapses have the potential to trigger a deep weak layer near the base of the snowpack, which would result in a very large and destructive 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

Valid until: Apr 18th, 2018 2:00PM