Avalanche Advisory Archive Pre-2016
Date Issued: | 2013-03-16 |
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Danger: | 2 |
Trend: | 2 |
Probability: | 3 |
Size: | 2 |
Problem: | 0 |
Discussion: | The National Weather Service Forecasts- TODAY...MOSTLY CLOUDY. SCATTERED SNOW SHOWERS. HIGHS AROUND 33. EAST WIND 5 TO 15 MPH. TONIGHT...MOSTLY CLOUDY. ISOLATED SNOW SHOWERS. LOWS AROUND 24. EAST WIND 5 TO 15 MPH. SUNDAY...MOSTLY CLOUDY. ISOLATED SNOW SHOWERS IN THE MORNING. We received roughly 5-8cm of new snow yesterday around the region. The winds died off. The new snow is probably fairly stable. The greater concern lies in the windslab this new snow is resting on. Earlier this week we had several natural avalanches on mostly south and SW facing slopes due to windloading. This shows us there is the ability to easily innitiate avalanches as the slopes are at a near state of natural instability. Over time these weak layers have the ability to heal. As you change the loction and the magnitude of the trigger, I assume you could still find pockets of weakness for human triggered avalanches. Be cautious and conservative in your routefinding. With not much new snow, wind, or warming in the forecast today avalanche danger will fall slowly over the next 24 hours. Be careful out there and have a great day! |
Tip: | How Snow Fails and fractures: Avalanches don't \"strike without warning\", as we so often read in the press. They are only the most spectacularly visible event in a long series of precursors leading up to the grand finale. It all begins many hours--or even days--before, usually when new snow or wind-blown snow begins to pile weight on top of a buried weak layer. Added weight causes the underlying snow to deform; rapidly added weight causes snow to rapidly deform. On an inclined slope, the deformation tends to concentrate within buried weak layers in the form of shear. Slow deformation rate Medium deformation rate Rapid deformation rate Having said this, scientists still don't know exactly how avalanches fail and fracture because snow is such a devilishly difficult substance to study. First, large variations commonly exist over both distance and time and second, as you can imagine, catching a natural avalanche in the act is stupendously difficult and dangerous, or as Monty Atwater put it, \"an occupation something like trailing a wounded African buffalo.\" So ten or twenty years from now, the following paragraphs--like so many of the \"facts\" we believe about avalanches--may seem like yet more quaint, geezer-ramblings. Nevertheless, this is what scientists generally believe about how avalanches fail and fracture. Fracture When a person triggers an avalanche, it means that they have found a trigger point of the avalanche. Perhaps it?s a place where the slab is thinner allowing more of the victim?s weight to tickle the weak layer. Perhaps it?s a place where the weak layer is more poorly bonded than the rest of the slope. I don?t think anyone knows for sure. But we do know that snow is very sensitive to the rate at which it is deformed and the extremely rapid deformation caused by the weight of a person is exactly the kind of thump needed to intiate the fracture process. Without this final trigger, unstable slopes can teeter on the brink of disaster for quite some time, giving us the illusion that all is well. After a storm, we never know how many slopes would come down if they just had a proper trigger. But with enough good snowmobiles and skilled riders, we can certainly find out. As avalanche researcher Rand Decker likes to say, \"Avalanches are like a bar room brawl. No matter how much tension you have, you need to give somebody a thump to get things going.\" |