Avalanche Forecast

Issued: Mar 22nd, 2016 9:19AM

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

jlammers, Avalanche Canada

Northwest Inland.

The Avalanche Danger may change quickly in the spring. Even brief periods of sun or rain can trigger pushy loose wet avalanches or promote destructive cornice falls.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Wednesday

Weather Forecast

On Wednesday expect 5-10cm of new snow with strong southwest ridgetop winds while continued light snowfall (5-8cm) and decreased winds are forecast for Thursday. Clearing skies are forecast for Friday as a dry ridge of high pressure develops over the province. Freezing levels should hover between 1100 and 1200m for the forecast period.

Avalanche Summary

In recent days a natural cornice fall triggered a size 3 slab avalanche in the southwest corner of the region. The avalanche occurred on an east aspect in high alpine terrain and stepped down to a few persistent weak layers from January and December. This avalanche demonstrates how a cornice fall can trigger layers that may otherwise be difficult to trigger. On Monday loose wet avalanches to size 2 were reported to have occurred in steep terrain on a variety of aspects. They failed in response to periods of solar warming or rain. New wind slab activity is expected in response to new snow and strong winds on Wednesday.

Snowpack Summary

In some areas, a dusting of new snow overlies wind slabs in exposed high elevation terrain and settled dry (and faceting) powder on shaded and sheltered slopes. Spring conditions have continued to develop. With that, lower elevation and sun-exposed slopes will likely appear moist or refrozen. A layer of surface hoar from early March can be found down 50-70cm but only seems to be a problem for the northern half of the region. Professional operators are still tracking two deep weak layers from early-January and early-February which can be found down about 1m or more. These layers have been dormant for a couple weeks but could wake up with substantial warming or a heavy trigger (like a cornice fall). Basal facets exist in most areas and have recently become reactive in the north of the region

Problems

Wind Slabs

New snow and strong winds forecast for Wednesday will promote new wind slab formation in exposed high elevation terrain. New wind slabs are expected to increase in size and reactivity throughout the day.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Cornices

Natural cornice releases remain an ongoing concern for professionals in the region. During the past week, falling cornices have also triggered large avalanches on the slope below.

Cornices become weak with daytime heating. >Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

A few persistent weaknesses exist in the mid and lower snowpack (see snowpack description). These potentially destructive layers may become reactive with spring warming or with a large trigger such as a cornice fall.

Be aware of thin areas that may propagate to deeper instabilities. >Be aware of the potential for full depth avalanches due to deeply buried weak layers. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 23rd, 2016 2:00PM