Avalanche Forecast

Issued: Apr 16th, 2018 4:22PM

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

jmcbride, Avalanche Canada

Cariboos.

Storm slabs are present at treeline and above, while loose, wet avalanches are a concern on sunny and lower elevation slopes. Be mindful of hazard from large cornices overhead, especially if it's sunny or warm.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Cloudy, flurries. Accumulation up to 4 cm. Ridge wind light to moderate, northwest. Alpine temperature near -5. Freezing level 600 m.TUESDAY: Mostly cloudy, light flurries. Accumulation up to 3 cm. Ridge wind moderate, northwest. Alpine temperature near -7. Freezing level 1500 m.WEDNESDAY: Mix of sun and cloud. Ridge wind light, southwest. Alpine temperature near -4. Freezing level 1700 m.THURSDAY: Increasing cloud. Ridge wind moderate, southwest. Alpine temperature near -2. Freezing level 1800 m.

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, 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.

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 most-recently buried 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 is still 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

Storm Slabs

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

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

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.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3.5

Loose Wet

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

If triggered, loose wet sluffs may step down to deeper layers resulting in large avalanches.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

Possible

Expected Size

1 - 2.5

Valid until: Apr 17th, 2018 2:00PM