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backcountry Advice 701

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Now that winter seems to have found its way back into our region, we must evaluate what effect the nearly two weeks of spring-like weather and temperatures have had on the snowpack. As is the case with almost anything you can think about, change will bring both good and bad.

The big daddy of instabilities this season has been the Nov. 17 rain crust/facet weakness. There was a facet layer on the summer firn snow and/or glacier ice before the November crust, but that was mostly destroyed by the same November rains that eventually led to the crust weakness. There is also the surface hoar that has formed below treeline at various stages throughout the growth of the pack.

Stability tests of the November weakness have been indicating hard or unreactive shears for the past week. The mid-pack above this has become rather hard, and the shears in the upper pack have been moderate. There has been no mention of these buried instabilities releasing lately either.

The snowfall since Christmas has been accumulating slowly, while temperatures have remained cool and winds light to moderate. In the ski areas the bed surface below this “dust” is rock hard. Outside the areas the old snow surface isn't as hard on North aspects, but South and West aspects have refrozen ice crusts very similar to those within the ski area boundaries. The new snow is not sticking to these hard surfaces.

The hazard associated with the new snow is somewhat lower than it might usually be due to its low density. This has been a little problematic when forecasting the hazard, as the destructive force has been low despite the high frequency of avalanche activity. Any changes to the temperature or wind trends that significantly increase the load over the new snow could quickly increase the hazard. A layer of low density snow sandwiched between hard snow and a denser layer of, say, windslab could lead to some very easily triggered and fast moving avalanches.

So the buried weakness' are less of a problem following the warm conditions we had in early December, but the surface layers are ripe for a growing hazard. The hazard rating for Jan. 3, 2000 is moderate, but the stability is Poor. There is snow in the forecast. The hazard will change quickly. Check with the local ski patrol for up to date information, or call the Canadian Avalanche Association for up to date information.

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