Avalanche Forecast

Issued: Mar 1st, 2017 4:53PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Deep Persistent Slabs.

swerner, Avalanche Canada

Northwest Inland.

Strong to Extreme winds accompanied by 5-10 cm will likely build reactive wind slabs. Deeper slabs may exist on leeward slopes.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Wednesday night-Thursday: snow amounts 5-10 cm with light winds gusting extreme from the SW. Alpine temperatures near -3 and freezing levels 1000 m. Friday: Periods of snow 2-7 cm. Ridgetop winds light gusting to 65 km/hr from the SW. Alpine high of -8 and freezing levels falling to 500 m. Saturday: Mostly cloudy with sunny periods. Ridgetop winds generally light. Alpine temperatures high of -10 and freezing levels at valley bottom.

Avalanche Summary

On Tuesday, no new avalanche activity was reported. With forecast snow and strong winds, reactive wind slabs are likely over the next several days.

Snowpack Summary

New snow 5- 15 cm accompanied by strong- extreme SW winds is burying a plethora of old snow surfaces including isolated wind slabs and wind press, sun crusts, and surface hoar. The new snow may have a poor bond to these interfaces. At treeline elevations the average snowpack depths are 150-190 cm and a well consolidated mid-pack of approximately up to 100 cm sits above weak basal facets (sugary snow) near the ground. Recent snowpack testing has shown sudden results down 100 cm within the facetted snow. Although possibly a low probability for triggering the persistent slab exists, the consequence would be high as it has the potential to produce very large destructive avalanches especially in shallower snowpack areas.

Problems

Wind Slabs

Strong to extreme SW winds and new snow will build fresh wind slabs on leeward slopes and behind terrain features. Loose dry avalanches may be easily triggered below treeline or in areas sheltered from the wind.

Use ridges or ribs to avoid pockets of wind loaded snow.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Deep Persistent Slabs

A lingering weakness at the bottom of the snowpack may remain sensitive to human triggering, especially in shallow snowpack areas. Smaller avalanches in motion also have the potential to step down and trigger deep persistent slabs.

Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Mar 2nd, 2017 2:00PM