Avalanche Forecast

Issued: Apr 14th, 2018 4:39PM

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.

Snow and strong winds have formed wind slabs in alpine lee areas and exposed treeline features. These slabs may be poorly bonded to the underlying crust. Watch for sluffing in steep terrain and loose, wet releases on sunny and low elevation slopes.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Mostly cloudy, flurries. Accumulation 2-4 cm. Ridge wind light to moderate, south. Alpine temperature near -6. Freezing level 500 m.SUNDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind light, east. Alpine temperature near -5. Freezing level 1700 m.MONDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light to moderate, east. Alpine temperature near -3. Freezing level 1900 m.TUESDAY: Mostly cloudy, light flurries. Accumulation 2-8 cm. Ridge wind light, northwest. Alpine temperature near -6. Freezing level 1500 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. There was also a report of a remotely triggered (from a distance) size 1 wind slab in an east-facing gully at 2300 m.On Tuesday a natural size 2.5 cornice failure on a north facing alpine feature did not produce any additional avalanche activity when it impacted the steep slope below. A natural size 2.5 wind slab was also observed on a cross-loaded east facing feature at 2400 m.On Monday steep solar aspects produced natural loose wet avalanches to size 2 between 2000 and 2600 m. A size 3 natural cornice failure was also reported from a north facing slope at 2600 m.

Snowpack Summary

A dusting of new snow covers a supportive crust on all aspects to at least 2100 m (and possibly higher on south aspects), while 20-40 cm of storm snow can be found at higher elevations. There are now a few different crusts in the upper 50 cm of the 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 60 to 140 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 are likely to remain reactive to human triggers on Sunday, especially in areas where a recent crust has been buried.

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

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.

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 and a bit of sun may destabilize surface snow, initiating loose wet avalanche activity especially on steep south facing features. At lower elevations, recent wet slides have released full-depth to ground.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Valid until: Apr 15th, 2018 2:00PM