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Avalanche Danger as a Continuum

02/08/2014

It is human nature to draw discrete boxes and categories around things. “That book is not science fiction,” “I’m a Mac person,” “Its just a class III rapid with big waves,” or “that’s a 5.11.” Then we pick and poke at the borders when things do not quite fit. “McCarthy writes lit-fic,” “but I use Gmail,” “at low water it’s got a class IV- entry” or “no, it’s only a 10c”.

Avalanche forecasters are no different. In our morning staff discussions, we will sometimes describe the danger to each other with phrases like “LOW side of MODERATE” or “on the cusp of HIGH.” It is like thinking of Avalanche Danger Ratings as a continuum instead of discrete boxes.

Partly that comes from the Avalanche Danger Scale itself. The five danger levels include multiple elements. There are five sections of travel advice describing how we think you should approach the snowpack. The Likelihood includes both triggered and spontaneous avalanches, and there are multiple combinations of expected Size and spatial Distribution. We can mix and match from the categories as necessary to arrive at a danger rating. That gives us many options to end up with a final danger that looks like a discrete category. For example, we can select a MODERATE (Level 2) danger when it is unlikely travelers will trigger an avalanche, but it will be very large (D3).

It might be worth visualizing the danger since late January. I’m going to generalize, but most of the forecast zones followed a similar pattern. At the end of the January dry spell, the avalanche danger was MODERATE (Level 2) near and above treeline. The problems were concentrated on just a few aspects.. The danger started to rise as snow accumulated, climbing quickly through CONSIDERABLE (Level 3) to HIGH (Level 4), where it remained during the Avalanche Warning.

Slide1

The danger fell into CONSIDERABLE (Level 3) the first few days in February. Wind events kept the danger at the upper end of CONSIDERABLE (Level 3), with natural avalanches possible as the winds drifted snow and overloaded some slopes. The danger eased slightly as the wind loading decreased. Starting February 3, modest amounts of snowfall provided additional loading and snow for transport. The snowfall was not sufficient to cause natural avalanching. Human triggered avalanches remained likely, well demonstrated by observers.

Slide2

Another storm is on the horizon. Snowfall looks more impressive than the last few days, and it will come with winds. We are anticipating the avalanche danger to rise again. How quickly is the question–will it jump on Friday or Saturday night, and skyrocket or slowly build?

Author: Spencer Categories: CAIC, Danger

December 23rd Website Changes

12/23/2013

We have been working to redesign our avalanche forecasts for almost two years. Over the process we have collaborated with other avalanche centers, communication specialists, and public messaging experts. You can see the result starting on December 23rd. We will be publishing more in-depth guides and explanations in the coming weeks, but here is a brief introduction to some of the changes:

  • Design: we have updated the look of the website. not only should it look more modern, but information should be easier to find.
  • New Observation Form: streamlines the process for submitting observations. If you log in, the form pre-populated based on your Prefs
  • New Forecast Format: the second-most obvious change. We will publish more detailed changes and guides to using the forecasts soon. Avalanche Danger will now be forecast for three elevation bands, rather than elevation and aspect. We will forecast avalanche danger for today and tomorrow, useful for planning. We have moved a lot of the text to graphics. This will display the information in a consistent format every day. In the graphics below, you can see that we are not reducing information, just re-arranging it and displaying some graphically. This streamlines the process for our forecasters, so forecasts should be out earlier.
  • Forecast Discussion: the second tab on the forecasts. Forecast Discussions are issued daily, but not on a fixed schedule. Discussions have no fixed format, and may include analysis of relevant observations, technical details on the snowpack, and musings on the impact of future weather.

NSJ_avy_prob2

Author: ethan Categories: CAIC, Uncategorized Tags: avalanche forecast

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