Avalanche Forecast

Issued: Jan 4th, 2017 4:10PM

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

triley, Avalanche Canada

Northwest Inland.

Hard wind slabs over weak facetted snow continue to be a concern for human triggering.

Summary

Confidence

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

Weather Forecast

Thin high cloud developing overnight with moderate west or northwest winds and alpine temperatures around -5. High cloud in the morning on Thursday with moderate to strong westerly winds. Cloud increasing during the day with a chance of flurries in the evening. Overcast with light snow on Friday, expect 2-3 cm by morning and another 3-5 cm during the day. Overcast with light snow or flurries on Saturday with alpine temperatures around -15.

Avalanche Summary

No new avalanches reported. In the north of the region near Ningunsaw there was a natural avalanche size 3.5 that released in the basal facets on Monday. This is a good reminder that large full depth avalanches are possible in shallow snowpack areas. A natural avalanche cycle with slides up to size 2 occurred Friday in the mountains near Smithers. This was in response to the strong northerly winds. Wind slabs will likely remain touchy throughout the forecast period, as sustained winds redistribute any loose surface snow. Deeper persistent weak layers will also remain a concern, it is possible to trigger large avalanches.

Snowpack Summary

The height of snow on the ground at treeline in most of the recreation areas in this region is about 100 cm. Deeper snowpack areas in the south and west of the region may have closer to 200 cm at treeline and up to 250 cm in the alpine. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard wind slabs. These wind slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak snow crystals near or at the ground.In addition to the sugary facets, you may find a layer of feathery surface hoar (up to 15 mm in sheltered areas), buried around 20 - 30 cm below the surface. There is another weak layer that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be found close to the bottom of the snowpack nestled in amongst the facets. We don't have a lot of information about these layers, but it's worth noting the layer responsible for most of the large avalanches during the big storm just before Christmas was the mid-November rain crust.

Problems

Wind Slabs

Wind slabs continue to be a concern for human triggering. Recent extreme winds have stripped some exposed north and east aspects and created variable depth deposits on south and west aspects.

Be cautious as you transition into wind affected terrain.Avoid travelling in areas that have been reverse loaded by winds.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

The lower snowpack is predominantly weak facetted crystals above a rain crust that developed in November. There are a couple of layers of concern in the mid snowpack, but I suspect that avalanches in motion may step down to the crust or smooth ground

Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Jan 5th, 2017 2:00PM