Avalanche Forecast

Issued: Apr 16th, 2018 4:28PM

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

jmcbride, Avalanche Canada

North Columbia.

Storm slabs will continue to build at treeline and above. Watch for loose, wet activity on sunny and lower elevation slopes. And 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 10-15 cm. Ridge wind light to moderate, northwest. Alpine temperature near -5. Freezing level 1000 m.TUESDAY: Mostly cloudy, light flurries. Accumulation 2-4 cm. Ridge wind moderate to strong, northwest. Alpine temperature near -7. Freezing level 1600 m.WEDNESDAY: Mix of sun and cloud, light flurries. Accumulation 2-4 cm. Ridge wind light, southwest. Alpine temperature near -4. Freezing level 1700 m.THURSDAY: Increasing cloud. Ridge wind light, southwest. Alpine temperature near -2. Freezing level 2000 m.

Avalanche Summary

Sunday's warm weather, rain and sunny breaks produced a widespread loose, wet avalanche cycle from size 1.5-3 on steep, solar aspects from 1600-2600 m, in the afternoon.Saturday there were reports from the southeast corner of the region of natural cornice and storm slab avalanche activity (size 2-3) on north and west aspects from 2500-2700 m.On Friday there were reports of a skier-triggered wind slab (size 1) on a steep, cross-loaded, southeast-facing slope at 2700 m. As well as a size 1.5, skier-triggered loose, wet release release in moist snow above a crust on a west-facing slope at 2000 m. Also on Friday a large cornice collapsed on a southeast aspect at 2500 m, with several 'bus-sized' blocks observed in the debris.Thursday there were reports from Glacier National Park of a size 4 wind slab that occurred overnight and is thought to have been cornice triggered on a north aspect at 2800 m.Wednesday there was a report of a natural cornice failure that resulted in a size 2.5 wind slab release (50 cm deep and 200 m wide) on a northeast aspect at 2600 m, north of Glacier National Park.

Snowpack Summary

About 30 cm of recent storm snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south aspects). While 40-50 cm of storm snow can be found at higher elevations in the alpine. Below 2200 m this new snow has a surface crust becoming moist or wet by the afternoon.Within the upper snowpack there are now a few different crusts with only the most-recently buried posing a concern with recent storm snow at upper elevations.There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 90 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but has not produced any avalanche 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 are generally considered dormant at this time but may be starting to become reactive to large triggers, such as a cornice collapse.

Problems

Storm Slabs

Recent widespread storm slabs may be poorly bonded to the crust below. Be very cautious with wind-loaded and cross-loaded slopes at treeline and above where these slabs may be especially deep and reactive.

Use caution in lee areas in the alpine and treeline. Wind and storm snow may form deep slabs.Sluffs may be easy to trigger in steep terrain that is sheltered from the windChoose well supported terrain without convexities.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Cornices

Large cornice failures have been reported in the past week. A cornice collapse may also have the potential to trigger a deep weak layer 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 - 4

Loose Wet

Warming temperatures or a bit of sun may destabilize surface snow and initiate 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 the loose wet sluffs may step down to deeper layers resulting in large avalanches.

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