Avalanche Forecast

Issued: Mar 24th, 2016 10:54AM

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

ghelgeson, Avalanche Canada

Northwest Inland.

Light snowfall and ongoing southwest winds are expected to continue to from fresh wind slabs at and above treeline this weekend.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

The Northwest Inland should see a steady progression of relatively weak frontal bands through the weekend. FRIDAY: Freezing level around 1200 m, trace of snow, light to moderate southwest winds. SATURDAY: Freezing level around 1300 m, 1 to 5 cm of snow, moderate to strong south/southwest winds. SUNDAY: Freezing level holding at 1200 m, 1 to 5 cm of snow, light variable winds.

Avalanche Summary

On Wednesday storm slabs to size 1 were reported on north/northeast facing terrain at treeline, running on the old melt freeze crust. Small loose wet avalanches below treeline were also reported. 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.

Snowpack Summary

In the last 48 hours 5 to 20 cm of new snow has fallen with moderate to strong southerly winds. At treeline and in the alpine small wind slabs are expected to have formed. These wind slabs overlie a variety of surfaces which include a hard crust on solar aspects above 1300 m, moist or refrozen snow on all aspects below 1300 m, and settled wind slabs in exposed high elevation terrain. A layer of surface hoar from early March can be found down 50 to 70 cm 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 1 meter or more. These layers are generally dormant but could wake up with substantial warming or a heavy trigger (like a cornice fall). Basal facets exist in most areas and have recently been reactive in the north of the region

Problems

Wind Slabs

Continued light snowfall and moderate southwest wind will likely continue to build fresh wind slabs at treeline and in the alpine. Wind slabs may be particularly reactive due to underlying hard surfaces.

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.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Cornices

Some cornices are the size of a bus, and will continue to grow with forecast snow and wind. Cornice collapses in the region continue to trigger large avalanches on the slope below.

Pay attention to overhead hazards like cornices.>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 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 25th, 2016 2:00PM